essay on bird migration

A Brief History of How Scientists Have Learned About Bird Migration

Bird migration is one of the most fascinating and inspiring natural phenomena—but how do scientists figure out where all those birds are going?

From the earliest origins of bird banding to high-tech approaches involving genomic analysis and miniaturized transmitters, the history of bird migration research is almost as captivating as the journeys of the birds themselves. My book Flight Paths , forthcoming in 2023, will take a deep dive into the science behind these techniques and the stories of the people who developed them, but in the meantime, below you can read a selection of milestones that trace our unfolding understanding of migration.

Early History

Indigenous cultures develop a range of legends and stories about migratory birds. Athabascan peoples in Alaska, for example, tell the story of “Raven and Goose-wife,” in which Raven falls in love with a beautiful goose but cannot stay with her because he can’t keep up when the family of geese migrates south over the ocean.

While Aristotle correctly recognized some aspects of bird migration in his Historia Animalium in the 4th century, BC, he hypothesizes that swallows hibernate in crevices and that some winter and summer residents are actually the same birds in different plumages.

Inspired by Aristotle, Swedish priest Olaus Magnus suggests that swallows hibernate in the mud at the bottom of lakes and streams. This misconception will persist into the 1800s.

English minister and educator Charles Morton theorizes that birds migrate to the moon for the winter. Although this sounds ridiculous today, he correctly conjectured that birds may be spurred to move to new areas by changing weather and a lack of food and even noted that body fat might help sustain them on their journey.

John James Audubon ties silver thread to the legs of Eastern Phoebe nestlings and identifies them when they return to the same area the following spring—or, at least, so will later claim. Biologist and historian Matthew Halley cast doubt on this in 2018 when he noted that Audubon was actually in France in spring 1805 when the phoebes would have returned.

German villagers shoot down a White Stork that had a spear made of African wood impaled in its side. Dubbed the “pfeilstorch” (or “arrow stork”), this unfortunate bird provides some of the first concrete evidence of migration between continents.

Ornithologist William Earl Dodge Scott is touring the Princeton University astronomy department when he’s offered a view of the full moon through a telescope. Astonished to see migrating birds silhouetted against the face of the moon, he is able to use his observations to calculate a rough estimate of how high they must be flying.

Climbing a hill outside Madison, Wisconsin, historian and amateur ornithologist Orin Libby counts 3,800 calls by migrating birds over the course of five hours on one September night. Many of the calls seemed “almost human,” he will later write, “and it was not difficult to imagine that they expressed a whole range of emotions from anxiety and fear up to good-fellowship and joy.” These calls will eventually be dubbed “nocturnal flight calls" and be used as one way of monitoring bird migration.

Hans Christian Cornelius Mortensen places metal rings around the legs of starlings in Denmark to study their movements, the beginning of the scientific use of bird banding.

At a meeting in New York City, members of the American Ornithologists’ Union vote to form the American Bird Banding Association, the direct forerunner of today’s USGS Bird Banding Laboratory. Its mission is to oversee and coordinate bird-banding efforts at a national scale.

The U.S. Bureau of Biological Survey assumes authority over the bird banding program after the Migratory Bird Treaty Act passes in 1918. The agency's Frederick Charles Lincoln will use banding records from waterfowl to develop the concept of “migratory flyways”—four major North America flight routes around which bird conservation is still organized today.

David Lack and George Varley, biologists working for the British government, use a telescope to visually confirm that a mysterious military radar signal is being generated by a flock of gannets. It’s the first concrete proof that radar can detect flying birds, but the idea is not immediately embraced: “At one meeting,” Lack later writes, “after the physicists had again gravely explained that clouds of ions must be responsible, Varley with equal gravity accepted their view, provided that the ions were wrapped in feathers.”

Louisiana State University ornithologist George Lowery’s moon-watching observations in the Yucatan, using techniques inspired by Scott’s original full moon observations in 1880, provide evidence that some birds do indeed migrate across the Gulf of Mexico instead of taking a land route over Mexico.

Oliver Austin, an ornithologist leading wildlife management in Japan under the Allied occupation that followed World War II, describes the traditional Japanese method of catching birds for food using silk nets strung between bamboo poles. Mist nets will soon become the primary method for capturing songbirds for ornithological research. 

George Lowery and his collaborator Bob Newman oversee a massive effort to recruit volunteers across the continent to record moon-watching observations during fall migration. “Telescopes swung into operation at more than 300 localities as people by the thousands took up the new form of bird study,” writes Newman. “By the end of the season, reports had been received from every state in the United States and all but one of the provinces of Canada.” Due to the difficulties in analyzing such large amounts of data without computers, Lowery and Newman will not publish the full results until 1966. Their work provides the first continent-wide snapshot of migration patterns.

Illinois Natural History Survey ornithologist Richard Graber and engineer Bill Cochran record nocturnal flight calls for first time, rigging up a tape recorder with bicycle axles to hold the six thousand feet of tape needed to record a full night of migration.

Richard Graber tags a migrating Gray-cheeked Thrush in Illinois with a miniature radio transmitter developed by Bill Cochran. That night, he follows it for 400 miles in an airplane as it continues its migratory journey. “Each of us, at times, must stand in awe of mankind, of what we have become, what we can do,” Graber will write in Audubon . “The space flights, the close-up lunar photographs, the walks in space—all somehow stagger our imagination. I was thinking about this as I flew south from Northern Wisconsin [the next morning], having just witnessed an achievement of another kind by another species.”

Ornithologist Sidney Gauthreaux, who studied for his PhD under George Lowery, publishes “Weather radar quantification of bird migration,” the first systematic study of bird migration patterns using the relatively new technology of weather radar.

Bill Cochran tracks a radio-tagged Swainson’s Thrush for 930 miles on its migration, following it from Illinois to Manitoba over the course of a week in a modified station wagon with a radio receiver sticking out of the top.

Johns Hopkins University's Applied Physics Lab carries out the first field tests of satellite transmitters on birds using the  Argos satellite system —launched in 1978 for the purpose of tracking oceanic and atmospheric data. Swans and eagles are early subjects. 

British seabird biologist Rory Wilson tracks the movements of foraging penguins using a device of his own invention that he calls a Global Location Sensor. It uses ancient navigation principles to calculate and record a bird’s location using only a tiny light sensor and clock. These devices will later be better known as light-level geolocators.

Canadian scientist Keith Hobson and his colleagues publish a paper demonstrating that it’s possible to determine where a migrating songbird originated by analyzing the amount of deuterium—a rare isotope of hydrogen that occurs in varying amounts across the landscape—in its feathers.

“Selective availability,” a U.S. government practice which intentionally limits the accuracy of GPS technology available for non-military use, is switched off. Ornithologists quickly begin creating GPS devices for tracking the movements of birds.

The Cornell Lab of Ornithology launches eBird, a community science platform that lets birdwatchers upload records of what they observe to a database that is accessible to ornithologists, ecologists, and other researchers. Today more than one billion sightings have been contributed from around the world. 

A satellite transmitter implanted in a Bar-tailed Godwit dubbed “E7” tracks the bird’s astonishing nonstop 7,000-mile migration from Alaska to New Zealand over the open water of the Pacific Ocean—“the equivalent,” according to a USGS press release , “of making a roundtrip flight between New York and San Francisco, and then flying back again to San Francisco without ever touching down.”

Ornithologists Kristen Ruegg and Tom Smith launch the Bird Genoscape Project, an effort to map genetic diversity across the ranges of 100 migratory species. It will enable ornithologists to identify where in North America a migrating bird came from by analyzing its DNA.

The Cornell Lab of Ornithology scientists kick off the second iteration of BirdCast , a project that uses weather radar data to predict nights of especially intense bird migration activity. (The original BirdCast, started in 2000 by Sidney Gauthreaux, was discontinued after a year due to the limits of the technology available at the time.) One major result of the project is initiatives that encourage cities to shut off disruptive nighttime lighting when large numbers of migrating birds are likely to be on the wing.

The Motus Wildlife Tracking System , which uses miniature radio transmitters and an automated network of ground-based receiver towers, is launched in Canada. More than 30,000 animals (mostly birds) will be tracked by the system in the next decade.

Light-level geolocators  confirm  long-held suspicions that Blackpoll Warblers, songbirds that weigh roughly the same as a ballpoint pen, make a nonstop 1,400-mile, three-day flight over the eastern Atlantic Ocean during their fall migration from New England to South America.

Project Night Flight,  the largest nocturnal flight call monitoring project to date, operates more than 50 recording stations in Montana’s Bitterroot Valley. Spearheaded by Kate Stone and Debbie Leick, staff members at private research and conservation property MPG Ranch, Project Night Flight will record more than 100,000 hours of data in the next two years.

Icarus,  a new space-based wildlife tracking system with receivers on the International Space Station, begins operations. The initiative's overseers aim to provide transmitters that are lighter, lower-cost, and provide better-quality data than any trackers used before.

This piece originally ran in the Spring 2022 issue as “A Brief History of Discovery.” To receive our print magazine, become a member by  making a donation today .

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Bird migration is one of nature’s great wonders. Here’s how they do it.

Some fly 11 days nonstop. Others trek 8,000 miles. Each year, thousands of bird species leave home in search of food.

Every spring and fall, a spectacle unfolds in the night sky as millions of birds attempt long, perilous journeys between their summer breeding and wintering grounds.

Most of the thousands of bird species that engage in this annual migration travel at night, when wind currents are smoother and the moon and stars guide their way.

The birds typically follow established flyways , generally north-south routes that offer the best opportunities for rest and refueling along the way.   Multiple bird species share these flight paths as they contend with rough weather, dehydration, starvation, and the threat of predation. ( Read more about the legendary treks of migratory birds .)

Arctic terns , for instance, undertake pole-to-pole roundtrips spanning more than 60,000 miles —a record, believed to be   the world’s longest migration of any animal . Other migrations involve birds flying east-west or up and down mountains. Even flightless birds migrate, such as the Adélie penguin , which makes a nearly 8,000-mile trek through frigid Antarctica.

Because migration is such an integral part of the avian life cycle, it was likely almost as prevalent thousands of years ago as it is today, says Martin Wikelski , director of the Max Planck Institute for Ornithology and a National Geographic Explorer .

Why some birds migrate and others don’t is the focus of a complex and active field of research. Finding food generally is believed to be the main driver. Additional motivations could include to escape from inclement weather and to reduce exposure to predators or parasites, especially during breeding season.

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New technological advances, such as sophisticated GPS tags and radar-detection systems, are giving scientists unprecedented opportunities to observe bird migration.

As part of his ICARUS project , for instance, Wikelski has outfitted some birds with Fitbit-like devices that track their movements and the environmental conditions they encounter.

These miniature solar-powered satellite transmitters could one day reveal animal migrations and behavior at a global scale from space.  

“There’s just so much to learn,” Wikelski says. “I’ve been tracking birds for over two decades, and the ease with which birds seamlessly migrate between worlds is absolutely astounding.”

Which birds migrate?

Roughly half of the world’s nearly 10,000 known bird species migrate, including several songbirds and seabirds, waterfowl and waders, as well as some raptors. The Northern Hemisphere has the most diverse array of migratory birds .

Among the most well known are Arctic-breeding bar-tailed godwits, champions of endurance. In 2020, scientists recorded a godwit undertaking the longest-known nonstop migratory flight between Alaska and New Zealand, traveling more than 7,500 miles across the Pacific Ocean for 11 days straight. ( Learn why birds matter, and are worth protecting.)

There are also feathered migrants that fly far and fast. The great snipe, for instance, covers distances exceeding 4,200 miles and reaches speeds of up to 60 miles per hour when traveling nonstop between Europe and sub-Saharan Africa, making it the fastest flying migratory bird.

Even tiny birds embark on gargantuan journeys.   Calliope hummingbirds—North America’s smallest bird—make 5,600-mile roundtrips between the high-elevation meadows and open forests of the northern Rockies and the pine-oak forests of Mexico.

Most species of migratory birds may be partial migrants , meaning that some populations or individuals within the species migrate while others stay put. A fraction of American robins, for example, remain near their breeding grounds across seasons while others travel south and then return north.

Yellow-eyed juncos breeding at high elevations along southeastern Arizona’s mountains are most likely to migrate up to a mile downslope during severe snowy winters, compared to those at lower elevations facing fewer food constraints. Even tropical birds , especially insectivores, undertake short-distance elevational trips.

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How do they know where to go  .

In addition to following celestial cues, such as the position of the sun, stars, and the moon, adult birds use a magnetic compass to navigate. Even when there are no landmarks, this internal “GPS system” can prevent them from getting lost.

Such navigational acumen can enable individual birds to move through regions not typically traveled. In experiments, when solo-flying common cuckoos were transported nearly 1,500 miles away from their breeding grounds prior to migration, they often steered back to their normal migratory routes.

But what about inexperienced birds migrating for the first time? In one experiment, geographically displaced young common cuckoos navigated back to roughly the same flight path used by those birds that weren't displaced from their home.   ( Read about amazing animal navigators .)

Whether this navigational capacity is inherited and innate or learned is an ongoing debate . “I think it’s a combination of innate tendency, but you learn from others on the way,” says Wikelski, who has been tracking common cuckoos since 2012.

One way to learn might be tuning into nocturnal flight calls from other migrating birds. Distinct from a bird species’ regular vocalizations, these acoustic signals could especially guide the inexperienced, sometimes even those of other species, Wikelski says.

How do they know it’s time to go?  

For some birds, changes in environmental conditions, such as the length of the day, may trigger migration by stimulating hormones, telling the birds it’s time to fly.

Birds’ internal biological clocks can also detect when a season shifts, using cues such as changes in light and possibly air temperature.

Once the birds are in migration mode, a feeding frenzy ensues. This allows the birds to accumulate fat to power their journeys, says Lucy Hawkes , a migration scientist at the U.K.’s University of Exeter who currently tracks Arctic terns.

“Somehow, [the birds] know that they have to migrate soon and get massive,” Hawkes says.

Local and regional weather conditions , such as rain, wind, and air temperatures can also influence decisions about when migratory birds take to the skies.

Migrating in a changing world  

Overall, migration schedules seem to be shifting, as a result of climate change . “It looks like bird migrations are commencing a little earlier in the spring,” says   Kyle Horton, an aeroecologist at the University of Colorado who uses radar technology to map realtime and historical bird migrations in the United States.

Black-throated blue warblers, for example, are migrating almost five days earlier now, on average, than they did in the 1960s. Canada-bound American robins are arriving 12 days earlier in the spring than they did in 1994. Migrating whooping cranes are showing up nearly 22 days earlier at their stopover site in Nebraska in the spring and leaving almost 21 days later in the fall than they did in the 1940s. ( Learn how climate change has affected the annual migration of the yellow warbler .)

Such early starts to migration may benefit birds if plant and insect productivity at the breeding grounds mirror the trend. However, not all migratory birds may be able to adapt to a warming world, and if they did, the full costs of doing so remain unclear.

As scientists continue to unravel the mysteries of bird migration, the phenomenon remains one of nature’s great wonders.  

“They’re flying all night, feeding all day, and doing it again,” Horton says. “That’s sort of remarkable."

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A bird’s migration decoded

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Simeon Lisovski is at the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Polar Terrestrial Environmental Systems, 14473 Potsdam, Germany.

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Miriam Liedvogel is at the the Institute of Avian Research, 26386 Wilhelmshaven, Germany, and also at the Max Planck Institute for Evolutionary Biology, Plön, Germany.

Migration is a ubiquitous feature of the animal kingdom, and is arguably studied most comprehensively in birds. Writing in Nature , Gu et al . 1 provide a range of insights into possible factors driving the evolution of migration in peregrine falcons ( Falco peregrinus ). These birds are probably best known for their record-breaking flight speed, which reaches more than 320 kilometres per hour when they dive for prey while hunting.

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The Avian Migrant: The Biology of Bird Migration

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The purpose of migration, regardless of the distance involved, is to exploit two or more environments suitable for survival or reproduction over time, usually on a seasonal basis. Yet individual organisms can practice the phenomenon differently, and birds deploy unique patterns of movement over particular segments of time. Incorporating the latest research on bird migration, this critical assessment offers a firm grasp of what defines an avian migrant, how the organism came to be, what is known about its behavior, and how we can resolve its enduring mysteries. The book clarifies key ecological, biological, physiological, navigational, and evolutionary concerns. It begins with the very first avian migrants, who traded a home environment of greater stability for one of greater seasonality, and uses the structure of the annual cycle to examine the difference between migratory birds and their resident counterparts. It ultimately connects these differences to evolutionary milestones that have shaped a migrant lifestyle through natural selection. Rather than catalogue and describe various aspects of bird migration, the book considers how the avian migrant fits within a larger ecological frame, enabling a richer understanding of the phenomenon and its critical role in sustaining a hospitable and productive environment. It concludes with a focus on population biology and conservation across time periods, considering the link between bird migration and the spread of disease among birds and humans, and the effects of global warming on migrant breeding ranges, reaction norms, and macroecology.

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Essay on Migration of Birds

Students are often asked to write an essay on Migration of Birds in their schools and colleges. And if you’re also looking for the same, we have created 100-word, 250-word, and 500-word essays on the topic.

Let’s take a look…

100 Words Essay on Migration of Birds

Introduction.

Bird migration is a fascinating natural event. It is the regular seasonal journey undertaken by many species of birds.

Why Birds Migrate

Birds migrate mainly due to changes in food availability, weather, or habitat. They travel to regions where living conditions are more favorable.

How Birds Migrate

Birds use a combination of the sun, stars, earth’s magnetic field, and landmarks to navigate during migration.

Challenges in Migration

Migration is not an easy task. Birds face threats like predators, harsh weather, and exhaustion.

Bird migration is a testament to nature’s wonder, showcasing the incredible endurance and navigation skills of these creatures.

250 Words Essay on Migration of Birds

Migration of birds is a complex and fascinating natural phenomenon. It involves the regular seasonal movement of birds, often north and south along a flyway, between breeding and wintering grounds.

The Process of Migration

Birds migrate to optimize their survival. During cold seasons, they move to warmer regions where food is abundant. The process is guided by several factors: genetic predisposition, day length, and changes in temperature. Birds navigate using celestial cues, the earth’s magnetic field, and landmarks.

Challenges and Adaptations

Migration is not without challenges. Birds face threats such as habitat destruction, climate change, and predation. To overcome these, they have evolved various adaptations. For instance, they accumulate fat reserves to fuel their long journeys and some species even sleep while flying.

Importance of Bird Migration

Bird migration has significant ecological implications. Migratory birds contribute to pollination, seed dispersal, and control of pests. Moreover, their migration patterns can indicate environmental changes, acting as bio-indicators.

Understanding bird migration is crucial for conservation efforts. As climate change disrupts migration patterns, studying and protecting these avian travelers becomes even more important. Indeed, bird migration is a testament to nature’s resilience and complexity, a spectacle that continues to captivate us.

500 Words Essay on Migration of Birds

Migration is a fascinating and complex behavior exhibited by many bird species. It’s a global phenomenon where birds travel thousands of miles, often crossing continents and oceans, to find the best ecological environments for feeding, breeding, and raising their young. This essay delves into the intricacies of bird migration, exploring the reasons, patterns, challenges, and implications of this remarkable behavior.

Birds migrate primarily for two interconnected reasons: food availability and breeding. Many birds feed on insects, nectar, or other food sources that are abundant in certain seasons but scarce in others. To survive, they must move to areas where food is plentiful. Similarly, birds often migrate to specific locations to breed, driven by factors such as food abundance for their offspring, fewer predators, and suitable nesting sites.

Patterns of Migration

Bird migration is not a random occurrence but follows specific patterns. These patterns are influenced by geographical features, weather conditions, and the Earth’s magnetic field. Birds generally migrate along established routes known as flyways, which include coastal routes, mountain passes, and river valleys. These routes provide the necessary resources such as food and resting spots for the birds during their journey.

Despite the evolutionary advantages, bird migration is fraught with numerous challenges. Birds face threats from predators, harsh weather conditions, and exhaustion. Additionally, human activities such as habitat destruction, climate change, and light pollution pose significant threats. Many birds die during their migratory journey, making it a high-risk, high-reward strategy from an evolutionary perspective.

The Science Behind Bird Migration

Bird migration is a complex behavior that is still not fully understood. However, scientists believe that birds use a combination of innate and learned behaviors to navigate during migration. They likely use the sun, stars, Earth’s magnetic field, and even their sense of smell to find their way. Recent research has also suggested that birds may be able to sense atmospheric pressure changes, providing them with information about favorable wind conditions for migration.

Implications of Bird Migration

Bird migration has significant ecological implications. Migratory birds can act as pollinators, seed dispersers, and even as a form of pest control. They also play a crucial role in the food chain. Additionally, bird migration has cultural and economic implications. Many societies celebrate the arrival and departure of migratory birds, and birdwatching is a popular and economically significant activity in many regions.

Bird migration is a remarkable phenomenon that illustrates the adaptability and resilience of nature. It is a testament to the intricate balance and interdependence of life on Earth. However, it’s under threat due to human activities, and its decline could have far-reaching implications. Therefore, understanding and conserving bird migration is not just about preserving a fascinating natural phenomenon, but also about maintaining the health and diversity of our ecosystems.

That’s it! I hope the essay helped you.

If you’re looking for more, here are essays on other interesting topics:

• Essay on Birds of a Feather Flock Together
• Essay on Birds
• Essay on Bill Gates

Apart from these, you can look at all the essays by clicking here .

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Bird Migration: Definition, Types, Causes and Guiding Mechanisms

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In this article we will discuss about the Migration of Birds:- 1. Definition of Bird Migration 2. Types of Bird Migration 3. Causes 4. Guiding Mechanisms 5. Disadvantages.

• Disadvantages of Bird Migration

1. Definition of Bird Migration:

The word “migration” has come from the Latin word migrara which means going from one place to another. Many birds have the inherent quality to move from one place to another to obtain the advantages of the favourable condition.

In birds, migration means two-way journeys—onward journey from the ‘home’ to the ‘new’ places and back journey from the ‘new’ places to the ‘home’. This move­ment occurs during the particular period of the year and the birds usually follow the same route. There is a sort of ‘internal biological clock’ which regulates the phenomenon.

Definition :

According to L. Thomson (1926), bird migration may be described as “changes of habitat periodically recurring and alter­nating in direction, which tend to secure optimum environmental conditions at all times” .

Bird migration is a more or less regular, extensive movements between their breeding regions and their wintering regions.

2. Types of Bird Migration:

All birds do not migrate, but all species are subject to periodical movements of vary­ing extent. The birds which live in northern part of the hemisphere have greatest migra­tory power.

Migration may be:

(i) Latitudinal,

(ii) Longitudinal,

(iii) Altitudinal or Vertical,

(iv) Partial,

(vi) Vagrant or Irregular,

(vii) Seasonal,

(viii) Diurnal and

(ix) Noctur­nal.

(i) Latitudinal migration:

The latitudinal migration usually means the movement from north to south, and vice versa. Most birds live in the land masses of the northern temperate and subarctic zones where they get facilities for nesting and feeding during summer. They move towards south during winter.

An opposite but lesser movement also occurs in the southern hemisphere when the seasons are changed. Cuckoo breeds in India and spends the summer at South-east Africa and thus covers a distance of about 7250 km.

Some tropical birds migrate during rainy season to the outer tropics to breed and return to the central tropics in dry season. Many marine birds also make considerable migra­tion. Puffinus (Great shearwater) breeds on small islands and migrates as far as Greenland in May and returns after few months.

It covers a distance of 1300 km. Penguins migrate by swimming and cover a considerable distance of few hundred miles. Sterna paradisaea (Arctic tern) breeds in the northern temperate region and migrates to the Antarctic zone along the Atlantic. It was observed that Sterna covers a distance of 22 500 km during migration!

(ii) Longitudinal migration :

The longitudinal migration occurs when the birds migrate from east to west and vice- versa. Starlings (Sturnus vulgaris), a resident of east Europe and west Asia migrate towards the Atlantic coast. California gulls, a resident and breed in Utah, migrate westward to winter in the Pacific coast.

(iii) Altitudinal migration :

The altitudinal migration occurs in moun­tainous regions. Many birds inhabiting the mountain peaks migrate to low lands during winter. Golden plover (Pluvialis) starts from Arctic tundra and goes up to the plains of Argentina covering a distance of 11 250 km (Fig. 9.54).

Birds migrate either in flocks or in pairs. Swallows and storks migrate a distance of 9650 km from northern Europe to South Africa. Ruff breeds at Siberia and travels to Great Britain, Africa, India and Ceylon thus travelling a distance of 9650 kilometers.

(iv) Partial migration:

All the members of a group of birds do not take part in migration. Only several members of a group take part in migration. Blue Jays of Canada and northern part of United States travel southwards to blend with the sedentary populations of the Southern States of U.S.A. Coots and spoon bills (Platalea) of our country may be example of partial migration.

(v) Total migration :

When all the members of a species take part in the migration, it is called total migration.

(vi) Vagrant or irregular migration :

When some of the birds disperse to a short or long distance for safety and food, it is called vagrant or irregular migration. Herons may be the example of vagrant or irregular migration. Other examples are black stork (Ciconia nigra), Glossy ibis (Plegadis falcinellus), spotted eagle (Aquila clanga), and bee eater (Merops apiaster).

(vii) Daily migration :

Some birds make daily journey from their nests by the influence of environmental factors such as temperature, light, and humidity also. Examples are crows, herons and starlings.

(viii) Seasonal migration :

Some birds migrates at different seasons of the year for food or breeding, called seasonal migration, e.g., cuckoos, swifts, swallows etc. They migrate from the south to the north during summer. These birds are called summer visitors. Again there are some birds like snow bunting, red wing, shore lark, grey plover etc. which migrate from north to south during winter. Th ey are called winter visitors.

Nocturnal and Diurnal Flight :

(i) Diurnal migration :

Many larger birds like crows, robins, swal­lows, hawks, jays, blue birds, pelicans, cranes, geese, etc. migrate during daytime for food.

These birds are called diurnal birds and gene­rally migrate in flocks.

(ii) Nocturnal birds :

Some small-sized birds of passerine groups like sparrows, warblers, etc. migrate in darkness, called nocturnal birds. The darkness of the night gives them protection from their enemies.

3. Causes of Migration :

Most species of birds migrate more or less on schedule and follow the routes in a regular fashion. The actual causative factors deter­mining the course and direction of migration are not clearly known.

The following factors may be related to the problems of migration:

i. Instinct and Gonadal changes :

It is widely accepted that the impulse to migrate in birds is possibly instinctive and the migration towards the breeding grounds is associated with gonadal changes.

ii. Scarcity of food and day length:

Other factors, viz., scarcity of food, shortening of daylight and increase of cold are believed to stimulate migration. Migration in birds depends upon two important factors— stimulus and guidance.

Scarcity of food and fall of daylight are believed to produce endocrinal changes which initiate bird migration.

iii. Photoperiodism:

The increase of day length (Photoperiodism) induces bird’s migration. The day length affects pituitary and pineal glands and also caused growth of gonads which secret sex hormones that are the stimulus for migration. In India, Siberian crane, geese, swan those come from central Asia, Himalayas, begin to return from March and onwards with the increase of day length.

iv. Seasonal variation:

The north-to-south migrations of birds take place under stimulus from the internal condition of the gonads which are affected by seasonal variation.

The experiments of Rowan with Juncos (summer visitor to Canada) have esta­blished that light plays an important role in the development of gonads, which has indirect role on migration. If the gonads undergo regression, the urge for migration is not felt. So the seasonal changes in illumination appear to be a crucial factor for determining migration.

Despite all these suggestions, it is not clear how birds — through successive generations — follow the same route and reach the same spot. The instinctive behaviours like migration, breeding, moulting are phasic occurrences in the annual cycle which are possibly controlled by the endocrine system. In all migratory birds, accumulation of fat takes place for extra fuel during prolonged flight in migration.

4. Guiding Mechanisms in Bird Navigation :

For more than a century the celestial navigations of birds have fascinated the ornithologists. Different explanations have been advanced to explain how birds navigate. It is difficult to generalize on the means of orientation and navigation in migration. The different groups of birds with different modes of existence have evolved different means of finding their way from one place to another (Pettingill, 1970).

The other reasons may be:

Fat deposition :

Migratory birds become greedy and fat is deposited in the subcutaneous region of the body. The fat deposition plays an important role in the migration of birds. Birds, those migrate a long distance, reserve enough fat which provides energy in their arduous jour­ney and helps the birds to reach its desti­nation, following a particular route. After fat deposition, restlessness (Zugunruhe) is seen among birds for migration.

Inherited instinct :

Birds that take part in migration or follow a more or less definite goal, evidently possess an inherited instinct. Both the direction and the goal must have been implanted in the bird’s genetic code when a population can adjust to a particular location or environment.

Experienced Lead the Flock :

The theory is sometimes advanced that old and experienced birds lead the way and thereby lead the whole route and show the whole route the younger generation. This the­ory may be applicable to some birds like swans, geese and cranes because they fly in flocks but not applicable in all species where old and youngs migrate at different times and mainly youngs start ahead of the adult.

Werner Ruppell of Germany, a leading experimenter on avian migration, found that Starlings of Berlin find their way back to their nestling places from about 2000 km away. A sea bird named Manx shearwater collected from the western coast of England after being flown by plane to Boston was found back in its nest in England within 12 days.

The shearwa­ter had flown its own way about 4940 km across the unknown Atlantic Ocean! The gold­en plover of North America migrates from its winter home in the Hawaiian islands to its breeding place in northern Canada.

This bird lacks webbed feet and it is quite natural that it must fly for several weeks over thousands of kilometers of ocean to reach its destination. The birds have wonderful power of navigation and orientation to find their destination even under odd conditions.

There are many theories regarding the phenomenon of migration in birds.

Various theorists propose that birds are guided by a number of agencies:

a. Earth’s magnetic field—as the guiding factor:

Some ornithologists believed about the existence of a “magnetic sense” as the impor­tant factor in the power of “geographical orientation”. The theory was conceived as early as 1885 but conducted by Yeagley in 1947 and 1951. Yeagley suggested that birds are sensitive and guided by the earth’s mag­netic field.

The Coriolis force arising from rotation of the earth plays the guiding role in migration of birds. The basic question of the theory may be asked — “can birds detect such minute differences in the earth’s magnetic field and can these forces affect bird’s behaviour?”

Attempts to demonstrate by experimental evidences have not supported Yeagley’s experiment. Experiments, in which the earth’s magnetic field was changed, had no effect on the direc­tion which the birds undertook.

b. Sun—the guiding agent in diurnal migration:

The concept that birds are guided by the position of the sun was advanced by Gustav Kramer in Germany and G. V. T. Matthews in England. They have shown by intensive experimentations those homing pigeons and many wild birds use the sun as the compass and that they possess a ‘time sense’ or ‘internal clock’ which allows them to take account of motion of the sun across the sky.

Kramer (1949, 1957, 1961) performed experiments on Starlings (diurnal migrants) and showed that these birds use the sun for setting their migratory course. When the sky remains clear, the Starlings succeed in taking the right direction.

If the sky remains overcast they become bewildered and fail to orient themselves. Mechanical placement of a mirror which deflects rays of the sun result into con­siderable deviation of orientation to a pre­dictable extent. The experiments of Kramer and others failed to explain the navigation and orienta­tion of night migrants. This aspect was exten­sively worked out by E.G.F. Sauer (1958).

c. Stars—the guiding agent in nocturnal migration:

The warblers and many other birds orient themselves during navigation by the sun during daytime. But the warblers as well as many other birds navigate mainly at night. What sorts of system do these birds use to the pathways during navigation at night?

Sauer performed experiments on white throat warblers to give an insight to the prob­lem. Sauer put the birds in a cage placed in a planetarium having an artificial replica of natural sky. When the light of the planetarium was poorly illuminated, i.e., when the stars were not visible, the warbelers failed to orient themselves.

When the illumination was better and the planetarium sky matched with the natural night sky, the birds followed up the proper direction. It has also been shown by Sauer that a warbler which has spent its life in a cage (i.e., never navigated in natural sky) has an inborn ability to follow the stars to navigate along the usual route the members of the species follow.

Sauer has suggested that the warblers possess hereditary mechanism to ori­ent themselves by the stars during nocturnal migration. The warbler can adjust the direc­tion perfectly at the latitude.

Suggestions have been advanced by many workers that the configuration of the coastline possibly helps in navigation, but Sauer has dis­proved the idea and advocated that the birds are exclusively guided by the stars during night.

d. The ‘compass’ and the ‘internal clock’ in bird migration:

It is a known fact that mil­lions of birds fly to their winter ‘home’ in every autumn. In doing so they cover often thou­sands of kilometers from their native ‘home’. In the following spring they again return to their breeding grounds. This is a regular bio­logical phenomenon in avian life.

It has been established that the young birds caught during migration, when released afterwards, follow exactly the original route their undisturbed fellows followed. This phe­nomenon suggested the presence of a sort of ‘compass’ the birds use during navigation.

But Kramer’s experiment gave a clue to the problem. The position of the sun is vital in con­trolling the navigation pathways. During the day the position of the sun in the sky is changed from east to west via the south. Despite such changes birds tried to navigate in the same direction. This means they have the inherent ability to make appropriate allowance for the time of day.

How do the birds know the time of day? They have possibly a built-in time­keeping mechanism (internal clock) which is synchronized with the earth’s rotation. The ‘internal clock’ can be made to synchronize with external happenings.

Existence of biological clocks is a pro­perty of living organisms. It is not confined to animals, it is found in plants and even in sim­ple cells too. It is a common experience that if we are in the habit of getting up every day at a particular time, we frequently wake up at the same time. Besides, many of our bodily func­tions have a rhythm of their own. These are possibly controlled by an ‘internal clock’ of which we are normally unaware.

Telemetry means methods of tracking of the movement of birds or other migratory ani­mals by using radio. This is the most promising method that has been applied to trace the route of bird’s migration. The method consists of attaching a small radio transmitter, weighing about 2-3 gm. that sends periodic signals or “beeps”.

The miniature transmitter can be placed on birds and it does not interfere flight and the signals can be detected by means of a receiving set mounted on vehicles or aero planes that can detect the routes of migratory birds.

Though there are some limitations of telemetry but this technology gives encoura­ging results. More recently researchers are engaged largely to track the routes of the migratory birds with the aid of satellites and radar tracking instruments.

5. Disadvantages of Bird Migration:

i. Many youngs are not, able to reach the destination because they die during the course of the continuous and tiresome journey.

ii. Sudden changes in the climate such as storms and hurricanes, strong current of wind, fog are the causes for the death of a sizeable number of migrants.

iii. Sometimes man-made high tours and light houses cause the death of migratory birds.

iv. Man themselves are responsible for the death of the migrants. They shoot at these poor birds just for their own leisure and amusement.

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Audubon Adventures

Background for Teachers

Note: This Audubon Adventures topic focuses on the Bird Migration Explorer, the digital tool created by Audubon and its partners to visually document the migration journeys of North American birds. For additional background on bird migration, please read the Background for Teachers essay for the topic “Birds on the Move,” which covers bird migration in general. That Audubon Adventures unit is referred to as you and your students engage with the Bird Migration Explorer and the related classroom activity.

Humans have long been captivated by migratory birds, awed by the animals’ biannual treks between their breeding and wintering grounds. The Bird Migration Explorer is a tool that allows anyone to follow hundreds of species on their epic migratory journeys. Users can pore over the movements of individual species, discover the birds that spend time at a specific location, and learn about the challenges these far-flying creatures face. The Explorer was created by Audubon and nine founding partners using science contributed by hundreds of researchers and institutions. It paints the most complete picture ever of the journeys of 458 bird species that breed in the United States and Canada.

The Explorer homepage features a colorful map composed of routes of more than 9,300 birds captured by tracking devices and shared by scientists across the Western Hemisphere. As Melanie Smith, program director for the project, says, “You can see how birds trace the outlines of continents, rivers, lakes, mountain ridges.” The Explorer will help conservationists who are seeking to identify and protect the places migratory birds need as well as members of the public who are curious about their seasonal neighborhood visitors. For educators like you, it is a powerful way to help students understand migration through classroom participation as well as self-directed explorations in which they follow their curiosity, pose questions, analyze data, test hypotheses, and identify answers. These are the hallmarks of the work scientists do. In other words, the Explorer offers a STEM-infused approach to learning that will serve students well throughout their time in school and in their lives beyond as engaged and informed members of society.

Which Birds, Where, and When

When you choose a species in the Explorer, you can see an animated map that shows where these birds are at any given time throughout the year. You can also see a brief description of that species and its habitat. A key takeaway is the ability to see how birds that spend time near you rely on an array of habitats across the hemisphere. Another view of the map lets users see how a single tagged bird connects people and regions across time and space. And yet another lets users explore the various conservation challenges a species faces in different places. These attributes of the Explorer offer many opportunities for further investigation by your class as a whole and/or for projects for small groups or individual students.

Why It Matters

Birds play a significant role in every habitat and ecosystem. They are connected to the plants and other animals that share a place in various ways. Birds need plants for places to rest, hide, and nest. Some depend on plants for food. Some plants depend on them for pollination or seed dispersal. Some birds feed on other wild animals—from insects and worms to fish, snakes, and even other birds. Birds are healthy when the places they pass through or live are healthy. Other livings things, including humans, need those places to be healthy, too. Being able to see which birds are going where, how many of them there are, and whether their patterns are changing, is important information scientists can use to evaluate the environmental health of a given place, a region, a continent, and even planet Earth. That same information is valuable to policy makers at all levels, farmers and other land managers, civic planners, and individuals as they make decisions that support the well-being of those to whom they are accountable or for whom they are responsible or concerned. For detailed help using the Bird Migration Explorer, click the “How to Use the Explorer” button on the Teacher’s Guide page for this topic.

New text/images tk.

Our planet runs on energy. Energy is defined as the ability to do work, to make something happen. Energy allows flowers to bloom, birds to sing, cars to move, televisions and lights to turn on, and the wind to blow. We—and all living things—wouldn’t exist without energy.

Most of Earth’s energy originates from the sun. The sun lights our planet and heats land, water, and air. Warming caused by sunlight makes the wind blow and ocean currents circulate. Energy from the sun also powers solar cells and wind turbines to produce electricity. Solar energy powers the planet’s carbon cycle, where energy flows from the sun to plants to animals. Plants turn solar energy into carbohydrates (e.g., sugars and starches) through photosynthesis, and in the process they absorb carbon dioxide from the atmosphere and release oxygen. Animals—including humans—eat the sugars and starches stored in plant tissues and require oxygen to convert carbohydrates into energy to move and grow. This conversion is called cellular respiration. So, plants absorb carbon dioxide and release oxygen and animals absorb oxygen and release carbon dioxide. In that sense they are “breathing buddies.” When plants and animals die and decompose, the energy returns to the ground or oceans. Burning releases it back into the atmosphere.

Energy Sources: Renewable or Not?

America’s primary and secondary schools spend more on energy each year ($6 billion) than on textbooks and computers.

The sun is a natural, renewable energy source. It won’t burn out anytime soon! Other renewable sources of energy include wind (which results from the sun warming the Earth’s surface), biomass (energy stored in wood, some crops, and animal and plant waste), geothermal (heat deep within the earth), and moving water.

Renewable energy is all around us, but most of the energy we consume to grow our food, power our technology, drive our transportation systems, and fuel our buildings and industries comes from nonrenewable energy sources—sources that can’t be replaced. Coal, oil, natural gas, and nuclear energy are our main nonrenewable energy sources. The first three are fossil fuels—formed from plants and animals that died millions of years ago. Over millions of years, their remains were covered by sediments whose weight compressed and heated these layers of organic matter into coal (a shiny black rock), crude oil (a thick, tarry liquid), or natural gas (a bubbling gas).

Fossil Fuels = Warming Planet

Burning fossil fuels is a main cause of global warming. Just as we exhale carbon dioxide during cellular respiration, burning coal, oil, and natural gas releases carbon dioxide. Carbon dioxide is the main contributor to the “greenhouse effect,” in which solar energy reaches the Earth’s surface but the resulting heat is prevented from escaping back into outer space. Burning fossil fuels that release carbon dioxide into the atmosphere has caused Earth’s average temperature to rise faster than ever before in recorded history. (Fourteen of the fifteen hottest years on record have occurred since 2000, with 2015 the hottest so far.) This increase in global average temperature is why we call it global warming . That warming trend, in turn, affects other aspects of climate, such as precipitation, storm patterns and the severity of storms, and so on. Taken together, those changes are referred to as climate change .

Electricity is a convenient way to distribute energy to our houses, stores, factories, offices and other buildings. The electricity that turns on the lights in the classroom when you flip a switch comes via wires, and may be generated by power plants burning fossil fuels. Burning these fuels to produce electricity is directly responsible for climate change as well as contributing to air pollution. Coal-burning power plants emit 2.5 billion tons of carbon dioxide to the atmosphere each year, making them the number one source of atmospheric carbon in the United States. Gas-powered vehicles are number two, adding nearly 1.5 billion tons of carbon dioxide.

Food Production Eats Energy

Between 10 and 20 percent of the energy used in the United States goes into food production. Thus, what we eat can greatly affect climate. Much of our food comes from industrial-style farms dependent on fossil-fuel-burning equipment and intensive use of synthetic fertilizers and pesticides, which themselves are made using fossil fuels. Transporting food between farm and table—an average journey of 1,500 miles—also requires fossil fuels. One of the most energy-intensive foods is grain-fed beef: Each calorie of meat requires 35 calories of energy to grow the grain, process and transport the meat, and refrigerate it in stores and houses. Food packaging also gobbles energy, both in production and disposal. It accounts for a third of household trash by weight and 10 percent of the average grocery bill.

Throwing Away Oil

Americans dispose of 1.7 million plastic bottles every hour, 24 hours a day. Plastic is made from petroleum, a fossil fuel. Manufacturing the plastic requires electricity, which uses more fossil fuels; transporting the bottles uses gasoline or diesel, also fossil fuels. So every time we “trash” a plastic bottle, we’re literally throwing away energy and contributing to climate change in a big way. One good way to reduce this wastefulness is to stop buying bottled water and start carrying refillable containers of good old tap water! Almost all tap water in the United States is pure, tastes good, and is completely safe to drink.

Facing Reality

The facts are clear, and it’s important to face them: Climate change is real and produces negative consequences for life on Earth right now. Audubon’s 2014 “Birds and Climate Change Report” uses empirical observations to identify and project the effects of a changing climate on North American birds. (See “The Audubon Report at a Glance.” ) The findings are sobering. Audubon’s study found that 314 North American bird species, nearly half of those studied, are at risk from climate change. Of those, 126 are projected to lose more than 50 percent of their current range by 2050. Many birds will need to either adapt or move in response, and we don’t know for sure if those that move will find all the resources they need to survive and reproduce.

Birds are like the canary in the coal mine. Climate change is warming the oceans, raising sea levels, and melting polar ice, which means it is affecting the lives of people and countless animals and plants, right now.

Switching to renewable, nonpolluting sources of energy such as solar, wind, and geothermal energy will help slow global warming by slowing the rate greenhouse gases are added to the atmosphere. Energy conservation helps, too: The less energy we use, the less greenhouse gases we add to the atmosphere and the less damage we do to our planet and the other species we share it with.

Saving Pikas and Other Wildlife

Helping Children Understand Climate Change

The National Audubon Society agrees with the United Nations and the vast majority of scientists worldwide that climate change is a fact and that it is caused by human activities. The dual nature of climate change—people caused it; people can take steps to remedy it—can empower children rather than simply scaring them. In other words, yes, there’s trouble, but there’s also hope for the future because human beings are smart and resourceful. Having recognized the problem, we can work toward solving it.

Children (and adults, too!) are often confused about exactly what climate change is. One source of confusion is the difference between weather and climate. It’s not uncommon to hear someone blame an unusually hot day on global warming or climate change, for example. One hot day is a temporary weather phenonemon. Years of increasingly higher average temperatures over a large region point to global warming and climate change. Addressing misconceptions and distinguishing fact from opinion are both important aspects of teaching and learning. Because climate change is a phenomenon that will affect life on Earth in increasingly apparent ways, preparing yourself with the latest and most authoritative information will help you prepare students for the future they will inherit.

Photo: Tara Tanaka/Audubon Photography Awards

• Bird Migration

CCB is a leader in conservation research involving bird migration

Populations of many migratory birds depend not only on places to breed and spend the winter but also on the quality and continued availability of habitats along migration routes. The importance of identifying and protecting these non-breeding habitats has been recognized by conservation organizations throughout the world and represents a formidable international conservation challenge. CCB continues to be a leader in migration research.

The broad objectives of our research program are to determine 1) the location of migratory pathways, 2) the resource and habitat requirements of birds in passage and 3) the ecological role that geographic areas play in the lifecycle of migrant species.

Whimbrel flying over Boxtree Creek on Virginia’s Eastern Shore, heading north to their Arctic breeding grounds. Photo by Alex Lamoreaux.

Migratory birds are on the move and nature-friendly farms can help them on their way

Assistant Professor of Ecology, Leiden University

Disclosure statement

Yali Si receives funding from the National Science Foundation of China and the Institute CML Impact fund of Leiden University.

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Every spring, hundreds of thousands of birds leave their winter habitat on Poyang, the largest freshwater lake in China, and fly north over the most densely populated region on Earth to reach their breeding grounds in Siberia. As with any long-distance journey you might take, these birds need to make stops where they can find a good meal and a chance to refuel.

Migratory birds must make use of food that is only available seasonally. Grass-eating birds like geese follow fresh, green shoots that appear as the season unfolds and the geese move northwards. The brief window when this young, spring grass is at its most nutritious and abundant can last as little as three weeks.

Such a fine-tuned strategy can become a liability. Geese can only eat when they arrive in the right place at the right time, but climate change has disrupted when and how long this seasonal food source is available. Migratory birds may arrive too late in one area if rising temperatures have ushered spring in earlier, for example. If birds cannot replenish their energy stores during migration they risk their ability to breed successfully when they reach their destination – and could even starve.

Along with colleagues, I have investigated the impact of climate change on 16 migratory waterfowl in Asia over the past 21 years. We compared how well a series of stopover sites on their migration route would fare as food sources as the climate changes and found that it is challenging for birds to solely rely on eating enough tasty grass to make the journey safely.

Fortunately, in other research which involved attaching satellite tracking devices to migratory geese and swans, we discovered other food sources on their route from Lake Poyang to Siberia.

Leftover seeds can help birds breed

I tagged 246 birds in total: 102 greater white-fronted geese, 74 tundra bean geese, 58 swan geese ( an endangered species ) and ten tundra swans which stopped over in the Northeast China plain before heading to their breeding grounds in Siberia.

Do the seasons feel increasingly weird to you? You’re not alone. Climate change is distorting nature’s calendar, causing plants to flower early and animals to emerge at the wrong time.

This article is part of a series, Wild Seasons , on how the seasons are changing – and what they may eventually look like.

Some birds can stay over a month in this region. Vast wetlands were once common here, offering important foraging and roosting areas for east Asian waterbirds preparing for the next leg of their journey to the high Arctic. Most have since been converted to cropland growing soybeans, corn, and rice.

The loss of wetlands as farmland has expanded and is a worrying trend globally. It has forced waterbirds to turn from natural vegetation to agricultural land as a source of food.

In the Northeast China Plain, migrating birds eat seeds left over after harvesting. As soon as the snow melts, these seeds are ready for hungry beaks to dig out. Leftover seeds mean that birds which do arrive before spring has started can still find sufficient food.

What’s good for the goose…

In fact, we found that birds tend to forage on seeds first and then shift their diets to spring vegetation as it emerges, taking advantage of both wetland and farmland habitats. Farmland seeds will become more and more important as natural habitats decline.

Mechanised harvests, which tend to leave more seeds in the field, could provide more food for birds. But protecting wetlands from destruction is still critical, and that will require limiting how much farmland is reclaimed and the intensity of cattle grazing. Lowering these forms of disturbance and encouraging bird-friendly tourism would help swans and geese use both types of habitat during their stopover.

If healthy wetlands accompany farmland, birds can eat natural vegetation when farmers sow their crops and so minimise their impact on crop yields. Seeing birds as part of the landscape, and not as intruders on farmland, can help preserve this biodiversity on the wing.

• Climate change
• Conservation
• Bird migration
• Migratory birds
• Wild Seasons

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Open Access

Peer-reviewed

Research Article

Modeling the Distribution of Migratory Bird Stopovers to Inform Landscape-Scale Siting of Wind Development

* E-mail: [email protected]

Affiliation The Nature Conservancy, Wyoming Chapter, Lander, Wyoming, United States of America

Affiliation Wyoming Natural Diversity Database, University of Wyoming, Laramie, Wyoming, United States of America

• Amy Pocewicz, 
• Wendy A. Estes-Zumpf, 
• Mark D. Andersen, 
• Holly E. Copeland, 
• Douglas A. Keinath, 
• Hannah R. Griscom

• Published: October 2, 2013
• https://doi.org/10.1371/journal.pone.0075363
• Reader Comments

Conservation of migratory birds requires understanding the distribution of and potential threats to their migratory habitats. However, although migratory birds are protected under international treaties, few maps have been available to represent migration at a landscape scale useful to target conservation efforts or inform the siting of wind energy developments that may affect migratory birds. To fill this gap, we developed models that predict where four groups of birds concentrate or stopover during their migration through the state of Wyoming, USA: raptors, wetland, riparian and sparse grassland birds. The models were based on existing literature and expert knowledge concerning bird migration behavior and ecology and validated using expert ratings and known occurrences. There was significant agreement between migratory occurrence data and migration models for all groups except raptors, and all models ranked well with experts. We measured the overlap between the migration concentration models and a predictive model of wind energy development to assess the potential exposure of migratory birds to wind development and illustrate the utility of migratory concentration models for landscape-scale planning. Wind development potential is high across 15% of Wyoming, and 73% of this high potential area intersects important migration concentration areas. From 5.2% to 18.8% of each group’s important migration areas was represented within this high wind potential area, with the highest exposures for sparse grassland birds and the lowest for riparian birds. Our approach could be replicated elsewhere to fill critical data gaps and better inform conservation priorities and landscape-scale planning for migratory birds.

Citation: Pocewicz A, Estes-Zumpf WA, Andersen MD, Copeland HE, Keinath DA, Griscom HR (2013) Modeling the Distribution of Migratory Bird Stopovers to Inform Landscape-Scale Siting of Wind Development. PLoS ONE 8(10): e75363. https://doi.org/10.1371/journal.pone.0075363

Editor: Claudia Mettke-Hofmann, Liverpool John Moores University, United Kingdom

Received: April 28, 2013; Accepted: August 13, 2013; Published: October 2, 2013

Copyright: © 2013 Pocewicz et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Funding: This study was funded by a grant from the Mayer and Morris Kaplan Family Foundation. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.

Introduction

Conservation of migratory birds requires an understanding of habitat, behavior and threats faced by birds during breeding, wintering, and migration. Migration is the most poorly understood of these annual activities, and of particular importance is understanding the distribution of stopovers and pathways used by migrating birds [1] . Recent technological advances, including telemetry devices, radar, stable isotope analysis, and genetic markers, permit the tracking of birds during migration [2] . Geographic Information System (GIS) modeling is also being used increasingly across large regions to evaluate conservation strategies and assess risks to migrating birds [3] , [4] .

One risk to migrating birds is wind energy development, which is expected to increase substantially in the United States in the coming decades due to evolving policies aimed at increasing renewable energy production [5] – [7] . Wind development can negatively impact birds through direct mortality from turbine collisions, avoidance behavior, and indirect effects of habitat fragmentation [8] – [12] . The U.S. Fish and Wildlife Service, Partners in Flight, The Wildlife Society, and the American Bird Conservancy, among others, have raised concerns about the long-term impacts of wind energy on bird populations [9] , [13] . Mortality related to wind turbines could have especially great effects on declining species and long-lived species with low fecundity, such as raptors [14] .

Wind development impacts to migratory birds may be reduced if facilities avoid major migration stopovers and flyways or if turbine operations are reduced in these areas during peak migration [13] , [15] . However, the lack of information on the distribution of migratory concentration areas, and their overlap with wind energy resources, impedes conservation and proactive development planning [16] . Several studies have examined bird migration patterns and modeled stopovers and pathways in the eastern U.S. [3] , [4] , but much less is known about migration patterns in the western U.S. [17] , especially in the Rocky Mountains. Limited regional information exists as incidental sightings [18] , migration counts [19] , [20] , local or species specific research reports, e.g. [21] – [23] , and expert knowledge, but has not been synthesized.

We developed a deductive modeling approach based on a synthesis of literature and expert knowledge concerning bird migration, and represented through GIS datasets, to map migratory concentration areas across the state of Wyoming. We produced deductive models due to concerns regarding the quality and quantity of available occurrence data needed to generate reliable inductive models. Deductive models, often referred to as habitat suitability models, are based on knowledge from literature or experts that is represented directly via environmental variables, while inductive models relate environmental variables to species occurrence locations using statistical algorithms [24] . Researchers have begun generating nationwide models depicting species’ distributions throughout the year based on inductive modeling of occurrences [25] ; these efforts contribute significantly to our understanding of migration timing at broad scales. However, these efforts are limited by a lack of occurrence data from migration seasons for sparsely populated areas like Wyoming, and by the inclusion of only a few general predictors of distribution. We were able to identify, create, and tune model parameter layers (e.g., topographic leading lines) that represent important drivers of local migratory concentration. It will likely be many years before there is sufficient occurrence data to model migration concentration across Wyoming using inductive methods, and there is an urgent need for these models now.

The goals of our research were to 1) create and test spatially-explicit models representing migratory concentration areas for four functional bird groups and 2) assess the potential exposure of bird migration concentration areas to future wind energy development, to illustrate the utility of migration concentration models for landscape-scale planning. Wyoming has abundant wildlife resources, relatively intact ecosystems, and also some of the nation’s best wind energy resources. Wyoming currently has nearly 1000 wind turbines, and an additional 5000 turbines could be installed during the next 20 years [26] . Wind development has the potential to impact bird populations within the state and beyond its borders, if development occurs without regard for migrating birds. The migratory concentration maps presented here provide preliminary data to companies and land management agencies planning for wind development in Wyoming, and our methods could be replicated in other places where maps of migration hotspots are lacking.

Our study area encompasses the state of Wyoming, which lies on the boundary between the Central and Pacific Flyways ( Figure 1 ). Wyoming’s several large mountain ranges are dominated by conifer forests and are the source of several major rivers. Sagebrush and other shrublands dominate the inter-mountain basins, and grasslands are found in the lowest elevations of eastern Wyoming.

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(A) Wyoming lies on the western edge of the Central Flyway and eastern edge of the Pacific flyway. Flyways are identified in varying shades of gray. (B) Key features influencing bird migration include topography (shown in brown shading) and major rivers (shown in blue). County boundaries are displayed for reference.

https://doi.org/10.1371/journal.pone.0075363.g001

Wyoming is the least populated state in the United States. Lands are primarily used for livestock grazing in the western two thirds of the state and for both crop production and grazing in the eastern third. Despite Wyoming’s low human population, much of the state is experiencing energy development [27] . In addition to extraction of fossil fuels, including coal, oil, and natural gas, Wyoming has received considerable interest in its wind energy potential recently due to wind resources that rank it 8 th out of the 50 U.S. states [28] .

Modeling Bird Migratory Concentration

We created models representing where four functional groups of birds concentrate in Wyoming during their migration. We focused primarily on groups of birds species that concentrate at stopovers during migration to stage, forage or rest [29] , because migrants that are concentrated in large densities are at greater risk for collisions with wind turbines [15] , [30] . We used functional groups having similar migration behaviors, because insufficient migratory behavior information and occurrence data are available for many individual species. The four functional groups were wetland birds, riparian birds, raptors and sparse grassland birds, and species represented by each group are listed in Tables 1 and 2 . Sparse grassland birds are those species that use sparsely-vegetated grasslands. All groups are comprised of species that concentrate during migration, except sparse grassland birds, which were included because many of these species are declining. We modeled spring migration patterns for wetland and riparian birds and fall migration patterns for raptors, because migration is most concentrated during these seasons for each group. We did not model both spring and fall migration for these groups, because we were most interested in when birds are most concentrated. For sparse grassland birds, we modeled spring migration because preliminary analysis indicated that our model was more indicative of spring than fall migrant distribution. We initially considered forest and shrubland birds but did not include them because they concentrate less during migration and may be partly represented by the riparian group, because they often follow riparian corridors during migration [17] , [21] , [22] , [31] .

https://doi.org/10.1371/journal.pone.0075363.t001

https://doi.org/10.1371/journal.pone.0075363.t002

The conceptual models were represented spatially using raster-based GIS data, at 90-m resolution, through commonly-applied methods for integrating multiple factors into suitability maps [77] . Raster cells in datasets representing factors (e.g., streams) were scaled from 0 to 1, where 0 = no importance for migration, 0.25 = low importance, 0.5 = medium importance, and 1 = high importance. Raster cells in datasets representing modifiers of factors (e.g., orientation of streams) were assigned values ranging from 0 to 2, where values of 0 reduced the importance of associated factors to zero, values of 1 left associated factor values unchanged, and values of 2 doubled the importance of associated factors in those locations. After multiplication by one or more modifiers, the value of an individual factor was normalized to range from 0 to 1. This normalization assured that each factor had the same relative importance in the model. However, for factors identified as being of greater importance than other factors, we multiplied that factor by a weight greater than 1 [77] . Finally, the individual normalized weighted or unweighted factors were added to cumulatively represent factors important to migration concentration. The final MIS values were normalized to range from 0 to 1.

More than fifty Wyoming bird experts, who represented state and federal agencies, non-profit groups, and the University of Wyoming, were identified and invited to provide input on a an earlier version of the models presented in this paper. We received feedback and suggestions from more than 25 of these experts through in-person and phone meetings and written comments, and we made modifications to the models based on this input.

Wetland bird migration concentration.

The wetland bird group includes waterfowl as well as birds that feed by wading in shallow water and mudflats along the shore of wetlands (hereafter “shorebirds”; Table 1 ). We identified that streams, wetland density, wetland size, and forage availability are important factors for wetland bird spring migration concentration, and that the importance of these factors varies with elevation, proximity to rivers, and location within or outside the Central Flyway. The model was implemented as: w 1 *(Streams)+w 2 *(Wetland density * Elevation * Proximity to river * Flyway location )+w 3 *(Wetland size * Elevation * Proximity to river * Flyway location )+w 4 *(Forage availability * Proximity to river )+w 5 *(Take-off/approach buffer), where modifiers are italicized and w 1 , w 3 , w 4 , w 5  = 1 and w 2  = 3. Value ranges of model factors and modifiers are described in Table 3 .

https://doi.org/10.1371/journal.pone.0075363.t003

Wetland birds generally migrate at night, stopping and feeding during the day. Wetland birds are among the species that attain the highest altitudes during migration, and are often capable of flying long distances (>3,200 km) non-stop unless forced by exhaustion or weather to land [32] . Wetland birds often use rivers to navigate during migration [32] – [34] . Rivers in the arid west may not only serve as navigation aids, but also a source of reliable stopover habitat in the form of reservoirs, off-channel wetlands, and agricultural fields [33] , [35] , [36] . Stopover habitat is typically similar to breeding habitat for a given species, though a wider range of resources may be used during migration [37] – [41] . Thus, stopover habitat for wetland birds includes marshes, wetlands, lakes, reservoirs, and other water bodies, e.g. [32] , [33] , [41] – [49] . In Wyoming, wetland birds concentrate in locations where wetlands are clustered in high densities. We weighted wetland density higher than other factors because its importance was emphasized by experts. This importance is also supported by the establishment of hundreds of national wildlife refuges for waterfowl encompassing important wetland clusters, and the use of these and similar wetland preserves by migrating waterfowl and shorebirds [32] , [46] , [50] . Larger lakes and wetlands can support large groups of migrating birds and provide safety from predators and are valuable even if not part of a wetland cluster. Heavy wing-loading in many wetland bird species can result in slow climbing rates [29] , [32] , placing them at risk of collisions with turbines during approach and take-off at stopover and foraging sites [30] , [51] . We buffered wetlands and streams by 1 km to account for long approach/take-off distances needed by many wetland birds [8] . Agricultural lands can also provide food for migrating birds at stopover sites [52] . Many species of ducks, geese, and gulls forage in agricultural areas with grain crops [32] , [53] – [56] , and some wetland birds forage in irrigated pasture or hay meadows [47] , [48] .

The importance of wetlands and foraging areas varies with location. Wetlands and foraging areas closer to major streams are more likely to be used because of the tendency of wetland birds to travel along rivers. Wetland birds are unlikely to use high elevation wetlands during spring migration, because they may still be covered with snow or ice. We reduced the importance value for clusters of wetlands when they were located at high elevations that would likely be under snow cover during spring migration, using an elevation cutoff suggested by wetland bird experts. Eastern Wyoming overlaps the Central Flyway, a major migration route for waterfowl, and thus tends to have higher concentrations of ducks and geese than the western portion of the state.

Riparian bird migration concentration.

The riparian bird group includes cuckoos and certain species of songbirds and flycatchers ( Table 1 ). However, the model will over-predict migration habitat for birds restricted to mature cottonwood forests, such as the Yellow-billed Cuckoo ( Coccyzus americanus ). Our riparian model may also represent some forest or shrubland migrants, which often follow riparian corridors [17] , [21] , [22] , [31] . We identified that streams and wetland density are important factors for riparian bird spring migration concentration, and that the importance of these factors varies with stream orientation, willow and cottonwood abundance, riparian structural diversity, elevation, and proximity to rivers. The model was implemented as: w 1 *(Streams * Stream orientation * Cottonwood abundance * Willow abundance * Riparian structural diversity )+w 2 *(Wetland density * Elevation * Proximity to river ), where modifiers are italicized and w 1  = 2 and w 2  = 1. Value ranges of model factors and modifiers are described in Table 4 .

https://doi.org/10.1371/journal.pone.0075363.t004

Riparian migrants concentrate along perennial streams where well-developed and structurally-diverse riparian trees and shrubs are present [17] , [21] , [22] , [57] , [58] . Riparian migrants are most likely to use larger, north-south oriented streams to guide migration [17] , [58] , and cottonwood and willow-dominated riparian areas are used more frequently than other vegetation types [17] . Isolated oases of riparian habitat are often found around large permanent wetlands and are important to riparian migrants, especially in arid landscapes like much of Wyoming [17] , [58] ; riparian birds will concentrate at permanent wetlands because of their riparian vegetation. Since riparian birds concentrate along large perennial streams, wetlands closer to these streams are more likely to be encountered and used as stopover habitat. Migrating birds will use all riparian areas in xeric landscapes, but lower elevation riparian corridors tend to be used by a greater number of species [22] , [59] . We used stream order as a surrogate for an elevation cutoff for streams, to avoid excluding large streams that occur at high elevations. Some migrants may use different routes in spring and fall, with lower elevation riparian corridors used more heavily in spring, when higher elevation riparian and forested areas are still snow-covered with fewer food resources [17] , [60] , [61] . We reduced the importance of wetlands when they were located at high elevations that would likely be under snow cover during spring migration. The stream factor was given twice the weight of the wetland density factor in our model, to reflect the especially high importance of streams and riparian areas to this group of birds [17] , [21] , [58] .

Raptor migration concentration.

The raptor group includes diurnal birds of prey ( Table 2 ). We identified that topographic features, updrafts, thermals, and streams are important factors for raptor fall migration concentration, and that the importance of these factors varies with topography and stream orientation and cottonwood abundance along streams. The model was implemented as: w 1 *(Topography * Topography orientation )+w 2 *(Updrafts)+w 3 *(Thermal formation)+w 4 *(Streams * Stream orientation * Cottonwood abundance ), where modifiers are italicized and w 1 through w 4  = 1. Value ranges of model factors and modifiers are described in Table 5 .

https://doi.org/10.1371/journal.pone.0075363.t005

Unlike many other migrants, most raptors do not maintain high altitudes during migration. Instead, they conserve energy by gaining lift from updrafts and thermals and gliding long distances, slowing losing altitude, to the next updraft or thermal [29] , [62] , [63] . Therefore, instead of concentrating at stopovers, raptors concentrate in areas that provide the best updrafts and thermals, especially during fall migration. Ridges and mountain ranges oriented perpendicular to prevailing winds produce the strongest updrafts. Although some ridges consistently provide strong updrafts, the location of updrafts can vary daily with local wind and weather conditions. As a result, when updrafts are not available, raptors will adjust their migration routes to take advantage of thermals, which form over surfaces that heat up the air faster (e.g. rock, sand, bare ground, pavement) [62] , [63] .

Prominent landscape features, including streams and topographic features such as tall ridges, provide leading lines that can guide raptor movements and concentrate migrants [62] , [64] . Leading lines that are oriented in the general direction of migration (north/south in Wyoming) are of particular importance, as are stream leading lines that include perching locations such as cottonwood trees. Some raptor species avoid crossing inhospitable habitat, such as deserts and large water bodies, and divert travel around the edges of these features [62] . Both leading lines and diversion lines concentrate migrating raptors, but we focused on leading lines because Wyoming lacks substantial diversion lines.

Raptor species likely not well-represented by this model include the Prairie Falcon ( Falco mexicanus ) and Peregrine Falcon ( Falco peregrinus ); they migrate at much higher altitudes and have dispersed and unique migration patterns [65] – [67] . Bald Eagle ( Haliaeetus leucocephalus ) [23] , Ferruginous Hawk ( Buteo regalis ) [68] , and Swainson’s Hawk ( Buteo swainsoni ) [69] migration patterns also do not fit this raptor model due to specific habitat needs.

Sparse grassland bird migration concentration.

The sparse grassland group includes species that use sparsely-vegetated grasslands or areas dominated by prairie dog colonies ( Table 2 ). We identified that grassland land cover types and presence of prairie dogs are important factors for sparse grassland migration concentration, and that grasslands having more bare ground are preferred. The model was implemented as: w 1 *(Land cover * Bare ground cover )+w 2 *(Prairie dog occurrence likelihood), where modifiers are italicized and w 1 and w 2  = 1. Value ranges of model factors and modifiers are described in Table 6 .

https://doi.org/10.1371/journal.pone.0075363.t006

In Wyoming, the sparsely-vegetated grasslands used by these birds during migration are relatively widespread. Therefore, in Wyoming, this group of migrants tends to exhibit a more dispersed pattern during migration than other avian species. This model is based largely on broad habitat requirements, because specific information on migration behavior for this group was generally lacking. Sparse grassland birds prefer short-grass and mixed-grass prairie and/or low shrublands with a high bare-ground component [68] , [70] – [73] . These species will often use heavily grazed, previously disturbed, tilled, and even somewhat degraded landscapes. Many sparse grassland birds, such as the Mountain Plover ( Charadrius montanus ), are often associated with prairie dog ( Cynomys spp.) colonies because of the close-cropped grass and high bare-ground components they provide [73] – [76] . Prairie dog colonies also provide a diversity of small mammal and avian prey for raptors, such as the Ferruginous Hawk.

Model Validation

The final predictive maps were validated using expert opinion and available observation data. Expert validation was completed through a web-based review of the final maps by statewide bird experts. We invited a larger group of experts to participate than for draft model feedback, but the majority of respondents had also been engaged in the first process. We asked experts to provide their assessment of each model on a 5-point Likert-type scale [78] that included rating selections of very poor (−1), poor (−0.5), okay (0), good (0.5), and very good (1) and to rate their level of expertise for each bird group on a 5-point Likert-type scale that included rating selections of very low (1), low (1.25), moderate (1.5), high (1.75), and expert (2). We multiplied the two rating values to weight each model rating by the reviewer’s level of expertise and averaged these expertise-adjusted scores for each model to obtain a final weighted-average score. Scores below zero indicated a poor model, scores of zero indicated an average model, and scores greater than 0 indicated a good model.

The observation-based validation used an occurrence dataset assembled from the Wyoming Natural Diversity Database ( http://www.uwyo.edu/wyndd ) and eBird [18] for each species represented by the models for the time period representing the majority of their typical spring or fall migration through Wyoming. From eBird, data were included only from exhaustive area, random, stationary and traveling counts. Migration time periods were extrapolated from species accounts in Birds of North America Online ( http://bna.birds.cornell.edu/bna/species/ ), eBird [18] , and Birds of Wyoming [79] ( Tables 1 and 2 ). We removed occurrences of questionable quality or with a spatial accuracy of less than 400 m. Next, for each bird group, we removed points that were closer than 800 m to a point deemed to be of better quality, based on mapping precision, recentness, and certainty of identification. Filtered occurrence points were subsampled to balance contributions of individual species, to minimize bias of validation statistics towards particular species with more occurrences, while still providing a minimum of 50 points for validation that were well-distributed across Wyoming. For each bird group, validation points were selected at random from filtered occurrences, stratified by species (see Tables 1 and 2 ). Up to 10 points per species were selected, where available.

We applied the Boyce index to measure observed versus expected occurrence, using the selected validation data points and binned versions of the models. Bins were created so that each bin contained approximately the same number of validation points. The Boyce index is a Spearman rank correlation between the area-adjusted frequency of validation points falling within a bin and the associated bin’s rank [80] . The validation points were ranked based on their predicted concentration score, and we chose the midpoints of the scores above and below the bin breaks as binning thresholds for the raster models. The Boyce index varies between −1 (counter prediction) and 1 (positive prediction), with values close to zero indicating that the model does not differ from a random model. Data were partitioned into 10 bins for each group, based on the model value assigned to the validation points, with exception of riparian birds, which had 8 bins. The bins in the riparian model were more limited in number due to a large proportion of raster cells with a predicted concentration score of zero and thus a large number of points occurring in the first bin.

Model Sensitivity and Uncertainty

We completed a sensitivity analysis of each of the four models to characterize the uncertainty associated with each model and describe how much the output of each model changed based on the contribution of each factor, modifier, or weight. We dropped each factor, modifier or weight one at a time from each model, and described the subsequent change in three ways. First, for each raster cell we calculated the percent difference between the partial model (missing one term) and the full model (all terms included), as the absolute value of the full model minus the partial model, divided by the full model. For each partial-model versus full-model combination, we calculated the mean and standard deviation of the percent difference across the study area. Second, we classified the full model raster and each partial model raster into 5-quantiles and, for each partial-model versus full-model combination, we tallied the number of raster cells having class agreement using the crosstab function in the R [81] raster package [82] . This resulted in an error matrix from which we calculated classification accuracy [83] , the percentage of raster cells in each partial model that were classed in the same bin as the full model. Finally, to visualize potential spatial pattern in uncertainty, for each cell in our study area we calculated the mean of the percent difference values across all partial-model versus full-model combinations.

Exposure of Migrants to Wind Energy Development

To assess the potential exposure of migratory birds to wind energy development, we measured the overlap between the maps of migration concentration and a predictive model of wind energy development potential. Our intent was to provide a coarse-scale analysis of where conflicts may exist with future wind development and to illustrate the utility of migration concentration models for landscape-scale planning. For these reasons, we used wind development potential rather limiting the analysis prescriptively to specific proposed wind farm projects. We created a predictive model of Wyoming wind energy development potential that incorporated wind resource potential, near-term development indicators and current development restrictions [84] . First, we fit a predictive model using maximum entropy methods [85] , [86] and Maxent® software version 3.3.3e. Maxent uses presence-only data, which was appropriate for this dataset because we did not have true absence data representing where turbines could not feasibly be built. The model used existing wind turbines as the response variable [87] . Predictor variables were the average 50-m wind resource potential [88] , percent slope, and topographic position (i.e., ridge, valley) [89] , because these factors influence the quality of the wind resource or feasibility of turbine construction (see [84] for details). We used a randomly-selected 67% of wind farms (643 turbines, 32 farms) to train the model and 33% to test the model (319 turbines, 8 farms), including all turbines within individual wind farms as either training or test data to avoid spatial autocorrelation. The model performed well, with a test area under the receiver operating characteristic curve (ROC AUC) of 0.91. A ROC AUC value of 0.5 indicates model performance no better than chance and values above 0.5 indicate increasingly strong classification to an upper limit of 1 [90] .

The Maxent® model represented the quality of wind resources but did not prioritize where development would most likely occur in the near term. Therefore, we adjusted the model results using short-term development indicators, including density of existing meteorological towers used to test wind speeds, distance to proposed transmission lines, proposed wind farm boundaries and land tenure [84] . Finally, we excluded locations where development was precluded due to legal or operational constraints, including protected lands (e.g. wilderness areas, conservation easements), airport runway space, urban areas, mountainous areas above 2743-m, and open water [84] . The adjusted model had a Boyce index of 0.89 (p = 0.001). A GIS version of the wind development model is available for download through the Wyoming Geographic Information Science Center (WYGISC).

We combined the wind potential dataset with each of the four migration model results to evaluate how much exposure migratory birds may have to future wind development. To understand spatial patterns in exposure, we first classified each of the five datasets into five quantile bins of potential for bird migration or wind development. This step was necessary to make the values comparable among the various models; while all models ranged from 0 to 1, the absolute values were scaled relative to each individual model. Values of 1, 0.75, 0.5, 0.25, and 0 were assigned to the quantile classes, where 1 corresponded to the quantile including the highest 20% of the data (i.e., very high). The wind potential and bird migration rasters with these new values were then multiplied, separately for each bird group. Where wind development potential was high (0.75) and migratory concentration was high (0.75), we assumed that exposure of birds to development would also be high (result = 0.5625) and that where wind development potential was low (0.25) and migratory concentration was low (0.25), exposure of birds would be low (result = 0.125). Therefore, we developed the following classes to reflect exposure level: very high (>0.75), high (0.56–0.75), moderate (0.26–0.559), low (0.1–0.259), or very low (<0.1). To spatially represent uncertainty in exposure, we determined exposure for each of the partial models and then calculated the standard deviation of the mean exposure across the full and partial models for each bird group.

Additionally, we focused on those areas with the highest likelihood for potential wind development – the top two quantile classes of high and very high – and summarized 1) the percentage of the top two migration quantiles for each bird group overlapping with these areas and 2) the percentage of the top two wind potential quantiles overlapping with the most important concentration areas for each bird group. We determined these percentages for the full models and also calculated the mean and 95% confidence interval across the full and partial models. Important migration concentration areas may not overlap spatially among the four bird groups, so we also combined the top two quantiles for each bird group into one raster representing cumulative migration concentration to generate the percentages described above.

The results for each model are presented as five quantiles in predictive maps, where the highest 20% of values are displayed as raster cells that are of greater importance for migration concentration than 80% of all cell locations ( Figure 2 ). GIS versions of the migration models are available for download through WYGISC.

Continuous modeled values were binned into five quantiles representing relative importance for migration concentration. Darker colors represent areas with greater importance, where >80% represents areas more important than those found across 80% of the state. The models represent (A) Raptor fall migration concentration (B) Wetland bird spring migration concentration (C) Riparian bird spring migration concentration and (D) Sparse grassland bird migration concentration.

https://doi.org/10.1371/journal.pone.0075363.g002

Model Validation and Sensitivity

The expert validation survey was completed by 13 (28%) of the invited experts. An additional seven experts provided comments but did not rate the models. The overall model rating was “very good” for wetland (score = 0.88, n = 12) and riparian birds (score = 0.97, n = 11) and “good” for raptors (score = 0.45, n = 10) and sparse grassland birds (score = 0.69, n = 11). Qualitative comments were consistent with the aforementioned ratings, with experts providing the most favorable comments about the wetland and riparian bird models and raising more concerns related to the raptor and sparse grassland bird models. We found significant agreement between species occurrence data and the migration models for wetland (p = <0.0001, Boyce index = 0.952), riparian (p = 0.001, Boyce index = 0.976), and sparse grassland bird migration (p = <0.001, Boyce index = 0.903) ( Figure 3 ). There was no agreement between occurrence data and the raptor migration model (p = 0.467, Boyce index = −0.030) ( Figure 3 ).

The observed to expected ratio in each quantile bin used to calculate the Boyce index for validation of migration models for (A) wetland birds, (B) riparian birds, (C) raptors and (D) sparse grassland birds. Models with a perfect fit show a monotonic increase as bin numbers increase, which is best illustrated in panel A.

https://doi.org/10.1371/journal.pone.0075363.g003

Model were most sensitive to the removal of base factors, such as streams for riparian birds, wetland density for wetland birds, and land cover for grassland birds ( Table 7 ). The raptor migration model was most sensitive to the updraft and thermal formation factors ( Table 7 ). Overall, uncertainty was lowest for the wetland bird model and highest for the sparse grassland bird model ( Figure 4a, d ). Across models, uncertainty tended to be greatest at higher elevations ( Figure 4a, b, d ).

These values represent the average percent difference of the partial sensitivity models (with one variable dropped at a time) from the full models. Locations with higher values are locations where the various versions of the model had the greatest differences, for A) wetland birds, B) riparian birds, C) raptors, and D) sparse grassland birds.

https://doi.org/10.1371/journal.pone.0075363.g004

https://doi.org/10.1371/journal.pone.0075363.t007

The potential for new wind development is highest in eastern and southeastern Wyoming ( Figure 5 ), and obviously exposure of migration concentration areas is also greatest within these areas of the state ( Figure 6 ). The spatial patterns in exposure varied among the four bird groups. For example, the highest exposures for grassland birds were mainly clustered in southeast Wyoming ( Figure 6g ), while high exposures for raptors were well-distributed along ridges throughout areas with high wind development potential ( Figure 6e ). Uncertainty in exposure to wind development ranged up to a standard deviation of 0.35 for wetland and riparian birds and 0.45 for raptors and sparse grassland birds ( Figure 6 ), on an exposure scale of 0 to 1 ( Figure 6 ).

Continuous modeled values were binned into five quantiles representing relative development potential and are followed by the percentage of the state’s area included in that bin.

https://doi.org/10.1371/journal.pone.0075363.g005

Exposure classes in each map are followed by the percent of the state occurring in that class. Uncertainty in exposure is represented by the standard deviation in exposure among the full and partial models for each bird group and is shown for (B) wetland birds, (D) riparian birds, (F) raptors, and (H) sparse grassland birds. Standard deviation is relative to an exposure value range of 0 to 1. Standard deviation classes in each map are followed by the percent of the state occurring in that class.

https://doi.org/10.1371/journal.pone.0075363.g006

Wind development potential was categorized as high or very high across 14.7% of Wyoming ( Figure 5 ). Important migratory concentration areas for each of the four bird groups were exposed to only portions of this area of high development potential ( Figure 6 ; Table 8 ). Sparse grassland bird important migration areas had the highest percent overlap with high wind potential areas and riparian birds the lowest ( Table 8 ). Seventy-three percent of the high wind potential area overlaps with important migration areas, when considered across all bird groups ( Table 8 ). This overlap is less for each individual group, and the individual values do not sum to the total because there is spatial overlap among migration areas for the various groups ( Table 8 ). The 73% of the wind potential area that overlaps with important migration areas corresponds with 13.2% of the important migration areas, across all four groups ( Table 8 ). Uncertainty in the two calculated percentages, represented by 95% confidence intervals, was low for all groups except sparse grassland birds ( Table 8 ).

https://doi.org/10.1371/journal.pone.0075363.t008

Models of migratory concentration for wetland, riparian, and sparse grassland birds were consistently rated as accurate representations based on validation from experts and existing datasets. These models provide a much needed initial assessment to highlight important resources for migrants where little is currently known, as is the case in Wyoming. The model set can be updated as new information on migration patterns or improved spatial data layers become available, and can be expanded to predict concentrations for other groups of birds or for individual species. Our approach could be replicated elsewhere to fill critical data gaps for migratory birds.

Our migratory concentration models can be used to inform siting of wind developments and identify where mitigation may be needed. These models are well-suited for the preliminary site evaluations recommended by the U.S. Fish and Wildlife Service (USFWS) to identify possible conflicts with habitats or species of concern at a landscape scale [13] . The USFWS implements the Migratory Bird Treaty Act, which prohibits the killing or harming of migratory birds, and wind energy developers are required to comply with this statute on both public and private lands. Our models could also be used by federal land management agencies, such as the Bureau of Land Management, to support regional planning for wind development on public lands. Preliminary site evaluations can identify where development might be avoided, and our models could also inform other stages of the mitigation hierarchy, including identifying potential mitigation offset opportunities [91] – where some important migration areas might be protected from development following impacts to other important migration areas. In locations where migratory birds concentrate and wind development cannot be avoided, a number of onsite mitigation techniques can be used to minimize risk to birds [8] , [13] , [15] . First, pre-construction surveys characterize bird use of project areas and aid in turbine placement that minimizes contact with birds and other wildlife. Second, minimal use of red or white flashing lights on wind turbines and associated infrastructure is much less likely to ‘draw’ migrating birds into the rotor-swept zone. Also, power transmission lines pose collision threats to migrating birds and should be minimized and buried when possible. Finally, post-construction surveys can help identify high mortality areas where additional mitigation measures may be needed, such as turning off high-risk turbines during peak migration times [15] . Our landscape-scale models are not a substitute for pre- or post-construction studies within project areas; mortality rates may be site-specific and depend upon the siting of individual turbines [92] .

The amount and location of exposure of migratory birds to wind development differed among the four groups of migrants. Not surprisingly, we noted the greatest potential exposure for sparse grassland birds, which use grasslands in the southeastern portion of Wyoming that havesome of the best wind resources. There was also the greatest uncertainty in exposure for sparse grassland birds, as that model relied heavily on grassland cover types, that when removed, shifted the important migration areas outside the geographic extent where wind development is anticipated. For sparse grassland birds, we expect that the overlap estimates with wind potential that are based on the full model including all three variables is the most accurate, due to the limited number of model factors. The raptor model performed poorly in validation against existing occurrence data, but we retained the model in the wind exposure analysis because it was rated well by experts and currently provides the only available spatially-synthesized information for raptor migration in Wyoming. The amount of exposure for raptors showed little variability among the full and partial models, suggesting that the model may offer a reasonable best estimate of exposure to wind development. Potential conflict was most limited for riparian birds, which are the most concentrated of the migrants, clustered primarily along valleys that generally have lower wind development potential. As a percentage of the total area of important migration concentration areas, overlap with the highest wind development potential areas was relatively low, ranging from 5.2 to 18.8%. However, impacts to these small relative percentages of the migration concentration areas could have a proportionally larger population impact. We expect that 60% or more of migrating individuals from each of these functional bird groups may be using the areas that we identified as most important (i.e., the top two model quantiles).

Our findings demonstrate that there are locations where wind facilities could be sited that may limit exposure of migratory birds to these developments. In 27.5% of the area classified as having high or very high potential for wind development, there was only low or moderate potential exposure of migratory concentration areas. Similarly, other studies have demonstrated that U.S. wind energy needs could be met by siting wind development in previously disturbed areas [93] and that mitigation requirements and associated costs could be greatly reduced by avoiding wind development in the most sensitive wildlife habitats [94] . Wyoming could exceed the U.S. Department of Energy’s wind energy goal for the state by 2662% even if development avoided sensitive biological areas [95] , not including the migratory concentration areas presented here.

Our models of migration concentration are limited by the availability and quality of bird occurrence data, predictive GIS layers, and information on migration behavior. The models represent where migration concentration is expected to be highest in most years based on fixed factors, but migration varies among years and is influenced by weather and variation in food resources. The Wyoming bird species occurrence databases contained thousands of records, but only a small portion of these corresponded to the migratory season. Further, most were opportunistic observations rather than data obtained through systematic, unbiased sampling, and some areas of Wyoming were underrepresented. The models were evaluated by experts and assessed against occurrence data, and a logical next step toward improving the models would be structured field validation. Although limited by available data, our migratory concentration models provide a useful spatial synthesis of the information that currently exists and fill a critical gap for landscape-scale planning.

We used the best available knowledge concerning factors that affect migration patterns to create the migration concentration models. For most bird groups, our modeling approach appears to have been effective, based on validation results, but the raptor model is a possible exception.

The raptor model performed well in the expert validation but poorly when compared to existing occurrence data. There may be factors influencing fall migration movement patterns that are not currently understood well enough, or the datasets or methods we used to represent important factors may be limited in some way. An alternative explanation is that the occurrence data are better suited for models of stopovers than for movement, as most observers record birds when they are perching or foraging. For all of the models, we selected model factors, modifiers, and weights based on literature review and expert knowledge. The sensitivity analysis showed that some of these model terms had a greater influence on the outcomes than others. The models were generally most sensitive to factors that affected a relatively large geographic extent (e.g., buffer in the wetland bird model or updrafts and thermals in the raptor model), or because they had been identified as the factor of greatest importance and been valued accordingly. Obviously we would expect the models to be influenced by key factors in this way, yet the sensitivity analysis remains informative because it provides an estimate of the degree to which model results may change given changes in knowledge or assumptions and it provides a range of uncertainty that can be compared with our estimates of bird migration concentration patterns. For the wetland and riparian bird models that had the most model terms, there was very little variation in model results when some modifiers were dropped from the model (e.g., cottonwood or willow abundance for the riparian bird model). This suggests that this modeling approach is robust to minor modifications and that it may be most important to focus on the key factors believed to drive migratory patterns. The sparse grassland bird model was the most sensitive to removal of model terms likely because of the small number of factors, and because we know the least about this group’s migration patterns and behavior.

Wind development has the potential to impact bird populations far beyond the localities of wind facilities if development occurs without regard for migrating birds that may breed or overwinter in other parts of the world. Although migratory birds are protected under international treaties, limited datasets are currently available representing migration at a scale useful to guide development or target protection. Our migratory concentration models provide preliminary spatial data to companies, land management agencies, and others planning for wind development at a useful landscape scale across the state of Wyoming. The migratory concentration models can also help to target conservation efforts for migratory birds, such as conservation easements and stopover habitat enhancements, and our methods could be replicated in other locations or for other groups or species of birds.

Acknowledgments

We thank Marissa Ochsenfeld, Kevin Contos, and Kristina Hooper for literature review, Kristi Gebhart for weather data, and Joe Fargione, Dan Petit, and Valerie Steen for comments improving an earlier manuscript draft. We are grateful to expert reviewers, including Marissa Ahlering, Jason Beason, Bryan Bedrosian, Frank Blomquist, Tim Byer, Anna Chalfoun, Doug Faulkner, Seth Gallagher, CJ Grimes, Allison Holloran, Stephanie Jones, Lorraine Keith, Jim Lawrence, Eric Lonsdorf, Brian Martin, Dave McDonald, Dave Mehlman, Chris Michelson, Bob Oakleaf, Andrea Orabona, Sophie Osborne, Bill Ostheimer, Chris Pague, Rick Pallister, Susan Patla, Chuck Preston, Matt Reddy, Larry Roberts, Jeff Smith, Patricia Sweanor, Steve Tessman, Nick VanLanen, Joni Ward, Nate West, Roger Wilson, and Sue Wolff.

Author Contributions

Conceived and designed the experiments: AP DK HG WE. Performed the experiments: AP MA WE. Analyzed the data: AP MA. Contributed reagents/materials/analysis tools: AP WE MA HC DK HG. Wrote the paper: AP MA WE.

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Essay on “Bird Migration” for School, College Students, Essay, Paragraph and Speech for Class 10, Class 12, College and Competitive Exams.

Bird Migration

In countries like England, France and North America, when the weather gets very cold in winter, rich people move to warm climates. We have seen rich people move to hill resorts and live there when the weather gets hot in summer.

The birds and animals also move from one place to another when the climate changes. It is one of the mysteries of nature that birds are able to travel thousands of kilometers and come back to their original resting places at regular intervals.

During September and November flocks of birds come from somewhere and then go away.

Bird watchers after years of patient observation and study of these migrating birds have concluded that there is a regular and systematic about their behaviour. People used to think that small birds such as Swallows, Nightingales and Cuckoos went to sleep during the winter; but now it is known that they go to warm countries.

Why do birds migrate? They are not directly affected by the cold because of their feather covering and warm blood, but in winter getting food is not easy.

Snow lies thick on the ground in winter and even lakes and rivers are frozen over. The weather is such that birds will not be able to catch either insects or fish. If they do not migrate, they will perish. As the nights are short the time available for searching for food is short, So, they have to fly over to warm places.

The birds fly to the same places and return to their original breeding grounds with amazing accuracy. During migration, it is usually the young birds that fly at the front and the older ones in the rear. Though the young ones have never flown that way, yet they fly to the right places and return to the right places covering hundreds of kilometers. They do not need any training in finding their direction during migration, for they are guided by instinct. Birds from north and north western parts of India fly to South India and Sri Lanka.

It is now found that some of the white strokes that are seen in India come from Germany.

Birds such as ducks and geese fly at a speed of between sixty-five and ninety kilometers per hour. Some birds fly from six to eleven hours a day. Some birds can fly 885 kilometers non-stop in about eleven hours. A bird known as the Eastern Golden plover which comes to India from western Alaska and North eastern Siberia flies 3200 kilometers non-stop. The snipe flies 4800 kilometers over the sea from Japan to Australia. There is scientific evidence to prove all this. They fly at a height of 1000 meters and 4000 meters above the ground.

More and more people are taking an interest in bird behaviour and in course of time, the answers to a lot of questions about bird migration will be available.

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How to Write an Essay on Birds: 9 Interesting Areas to Focus

How to write an essay on birds? There are some interesting facts you can write about. Information about birds can be an excellent source for a creative essay. Birds are found in every part of the globe, creating a large variety of species to write about, especially when well-researched. Interesting bird facts can create wonderful topics for an essay, including unique theses that a student can explore and develop an enjoyable piece of writing.

When writing an essay about birds, it’s important to consider researching these facts, especially their biological composition. For instance, one can write an essay about birds by highlighting some distinguishing characteristics between bird species. This type of writing would be most interesting in English, particularly due to the distinctive nature of scientific descriptions. You can also include a short note about their biological differences in each section to make the essay more appealing.

Interesting Facts for Writing an Essay on Birds

Feather distinction.

One of the most interesting topics for an essay on birds is their feather diversity. Birds have distinctive appearances in structure, order, and color. Feather distinction is one of the distinguishing characteristics between species. However, some species have different colors based on various biological and environmental factors. For instance, some bird species have distinctive differences between the feathers of a male and a female. In other cases, the differences may appear disorderly but are worth investigating.

Migration marvels and global distribution

Some bird species are migratory, traveling between regions, even continents. Since the migrations coincide with seasons, they create some migration marvels worth writing about. For instance, seagulls migrate between winter and summer, running from the cold weather. During their travels, the birds create awesome displays of their traveling routines, mating habits, and hunting traditions. This topic is most suitable for nature lovers, people willing to investigate many species for their beauty and scientific facts.

Nesting prowess

You can also write an essay on birds based on their architectural techniques. Birds build their nests differently depending on their size, primary predators, and location. While the weaverbird prefers loosely hanging tree branches, the penguin can only nest on the ground near mountains and ocean shores. The structure and composition of the nest also differ significantly, creating an array of architectural designs to compare. Any person interested in birds understands the importance of a nest, especially during mating and incubation.

Egg laying facts

Birds are oviparous or egg-laying animals in English. Different species lay different egg sizes, colors, and shapes. They have distinctive characteristics based on their egg-laying habits, including location and responsibility. Some birds, such as the Cuckoo , exhibit parasitic behaviors in brooding. They lay their eggs in other birds’ nests, forcing the foster parents to incubate a foreign egg and feed an adopted chick afterward. Egg-laying habits can be quite an impressive topic for an essay on birds, especially due to the amount of scientific evidence available online.

Sociocultural rituals

Another interesting concept you can write about birds is their social lives. Like humans and any other living thing, birds socialize on different occasions. Some live in large groups, while others are loaners. However, all birds have distinctive mating rituals. Some specials engage in colorful, elaborate courtship traditions. They display marvelous moves to attract mates, using their wings and, in some cases, their avian architectural prowess to assert dominance. Birds engage in long relationships that resemble marriage in humans. The bald eagle is a good example of a bird species that marries or mates for life. The differences in sociocultural behaviors can create an amazing topic for a good essay.

Cognitive capacity

Some bird species are worth writing essays about, especially those that have shown high intelligence. Students can investigate intellectual abilities in birds to find impressive topics for their term papers and final research. You can even hire an experienced academic writer to help with the information gathering and drafting. For instance, CustomWritings professional essay writing service is a prominent helper with over ten years of experience supporting students’ journeys. While intelligent avian is attractive, finding accurate and reliable supporting evidence on such a topic can be daunting. With professional assistance, you can access scholarly articles and integrate findings from research in your essay on birds.

Vocal abilities

Birds are also known for their vocalization capabilities. While students cannot transcribe bird songs into writing, investigations into singing abilities can constitute a good essay. Most importantly, one can research birds’ ability to vocalize or mimic different sounds. Some bird species are known for their vocalization, especially when imitating humans and other birds. Others can produce relatively unique sounds, making them an attractive piece of marvel for analysis.

Scholars and researchers tend to focus on the biological differences between birds. Notably, biologists have invested significantly in understanding the genetic differences for classification and knowledge gathering. With this information, students can develop exciting topics for their essays or end-term research papers. Another interesting point of focus is the survival instincts and abilities of birds. While some species rely on camouflage for safety, others are birds of prey. The details about each bird’s genetics can help explain distribution and preferences.

Life expectancy

Similarly, the biological differences explain the differences in life expectancy. It’s difficult to ascertain the length of life in wild birds due to constant migration. However, scientific evidence suggests that some birds live longer than others. A good essay writer would consider analyzing the reasoning behind these differences and identify genetic and environmental characteristics affecting the length of life.

How Do I Write an Essay on Birds?

The best approach for writing an essay on birds involves conducting sufficient research. A good student would start by identifying an interesting fact to write about birds and research it. The information gathered from the knowledge search can then be used to create a comprehensive essay topic with a compelling thesis. The interesting facts about birds can also be a good hook for the introduction. The essay on birds should be organized professionally, adopting a basic paper structure with an introduction, body, and conclusion.

Writing an essay on birds should also incorporate scientific and scholarly evidence. A good writer understands the need to integrate external sources with supporting and counterarguments. This approach will make your essay more interesting to read and easy to grade. Your professor may be impressed by your capacity to research a wild topic and investigate evidence found in scholarly works. Besides, supporting your arguments with reliable and verifiable arguments makes your writing believable. You can also impress the reader with ideas corroborating your knowledge of birds. For instance, you can integrate information about mating in an essay about birds’ vocal abilities to demonstrate a connection between the two issues. In the end, your essay about birds should be compelling and informative.

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Essay on Migration | Causes and Effects of Migration

December 3, 2017 by Study Mentor Leave a Comment

Animals and man have been ever travelling. From grassy plains to fertile land, in search of better food, better opportunities. ‘Migration’ means the movement of population from one place to another for better opportunities.

Table of Contents

What is Migration?

Everyone wishes to lead a happy and secure life. A place where they can offer security to their family and a better future both for themselves and family. Migration many be of two types- permanent and temporary. Some migration may also occur annually, seasonally, or diurnally. According to certain census it has been found that migration mostly happens in three stages- (a) rural to rural , (b) rural to urban , (c) urban to urban , and (d) urban to rural

Maximum migration is from rural to urban, especially in developing countries like India. Even urban to urban migration happens quite a lot. But migration of the type (a), (d) is very rare. Migration of type (a) happens only when a person goes from another village to sell his items during bazaar or Melas. Some migration also happens from rural to small then from small town to urban. Such type of migration is called step wise migration.

In India there is a crazy race of the population travelling from the rural areas to the metropolitan cities like Mumbai, Kolkata, Chennai, Delhi, Bangalore etc, seeking for better employment and better work opportunities. And this craze is increasing more and more in the coming years.

That is why competition in the job sector is increasing in the urban sphere. Metropolitan cities act a crowd puller. People are attracted to the vibrant colours of life in the cities. They fall in the wrong notion that they can pull up something big or great in the cities and earn a living but not everyone gets equal opportunities. Some end up rag-pickers, some end up as street dwellers, and some end up beggars who don’t get any means of livelihood.

Another term that comes along with migration is commutation. Commutation is the means of travelling on a daily schedule of the people to cities from the neighbouring towns and villages for the purpose of job and other works. This is a type of temporary migration.

Some people commute seasonally- incase or family gathering or wedding ceremonies. While some immigrants migrate annually. Migration is not just a re-location of human resources and settlements but it is a process which has three-fold impact:

(a) On the area experiencing immigration,

(b) On the area experiencing out-migration, and

(c) On the migrants themselves, the purpose of migration may be employment, business, education, family movement, marriage, calamity, etc.

These migrants have very little skill and professional expertise, moreover they lack literacy. They mostly get involved in the low grade activities and fields of manual labour, where there is not much sophistication or use of literary capabilities.

Very few are in administrative, professional or technical sphere. The condition of women migrants is worse. Majority of them are illiterate or have very little literacy. Such people take up even lower grade of jobs like the domestic maid servants, hawkers or vendors. This change has been termed by many as ‘evolutionary urbanization’.

This sudden migration burst has led in detoriation in the look of the city and spreading of cities. Rapid human pressure has led to the unprecedented growth of shabby towns, slums and bastees and squatter settlements. Cities are spreading far beyond its boundary limits.

There are also other evils like the overflow of urban unemployment, rapid exploitation of the items of daily necessity like- food, clothing and shelter and their unavailability and there is a very sharp decline of human values and moral and it is increasing over the years( as observed its increase from 1981-1999 and will steadily increase over the 21st century).

Hence the metropolitan cities are becoming like blown-up urban villages which fail to offer basic necessities of life to the people residing in it. Due to unchecked or unprecedented human growth the cities lack in urban functions, characteristics, urban infrastructure and services, and without a strong economic base.

They are slowly stepping towards what is called as ‘degeneration’ or ‘decay’.

The urban areas not only attract the poor and the illiterate class but it has become a place for the educated and elite class to earn a living and lead a comfortable and relaxed life. There have been many cases where students from villages have come in cities to get higher education, managed with a good job and become a part of the city itself.

Even some big landlords and rich farmers have shown their interest in investing a good part of their agricultural profits in the different businesses that goes on in the city and also commercial activities. Hence the cities of developing countries like India are developing on the plunder or the remains of the rural parts (both natural and human). Unless this exploitation of blood-sucking trend is terminated for once and for all, the development or the revival of the ‘desi’ villages is a farfetched dream.

Not just there are rural immigrants to deal with. There are international migrants as well. Majority of the international migrants to India come from Asian countries, which are in turn followed by Europeans, Africans, etc. The neighbouring countries like Nepal, Bangladesh, Pakistan, Sri Lanka and Russia etc. have contributed large number of migrants to India.

Since there is no restriction along Indo-Nepal international boundary large numbers of Nepali people come to India for seeking employment, education, business etc. Assam, West Bengal and north eastern states attract large number of legal and illegal migrants from Bangladesh.

This has created a number of social, economic and political problems in these areas. Nepalese are seen in Uttar Pradesh, Bihar, Punjab, Himachal Pradesh, Arunachal Pradesh, Maharashtra and Delhi. Similarly migrants from Sri Lanka are most frequented in South India especially in Tamil Nadu

Migration not only creates confusion and commotion, but also an ill-growth of cities. That does not mean that we will shun away the immigrants.

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Millions of birds may die while migrating through Texas. Here's why and how to help

Texas is a main flyover state for migrating birds , but due to major city lighting, these pathways can be dangerous. 

According to Audubon Texas, 365 million to 1 billion birds die each year from building collisions in the U.S. These incidents can increase when flocks of birds fly through major cities.

Approximately one of every three birds migrates through the U.S. in spring, and one of every four birds migrates through the U.S. in the fall.

Here's what to know about how populations are affected and how to help:

How many birds migrate through Texas?

According to Audubon Texas , the full migration season for birds is from March 1 to June 15. Approximately two billion migrating birds fly through the Lone Star State. 

According to the BBC , both the Central Americas Flyway , which stretches from the Canadian Arctic to the southern tip of Argentina, and the waterway-rich Mississippi Flyway , beloved by migratory waterbirds, pass through Texas. 

How does artificial light affect migration?

Artificial light in cities can confuse birds during migration, according to Environmental Evidence Journal. Birds tend to migrate by night and use the stars to navigate. By day, they use the Sun to orient themselves. During nocturnal migration, it’s common for birds to crash into lit-up windows and structures. This is a common occurrence in Texas cities like Galveston.

According to Texas Parks and Wildlife , nearly 400 migratory birds once crashed into the American National Building, a skyscraper in downtown Galveston, during a storm.

What can be done to prevent death during migration?

Defenders of Wildlife suggest building owners, businesses, developers and homeowners consider these options to help protect migrating birds:

• Turn off all non-essential lights from 11:00 p.m. to 6:00 a.m. each night during migration season.
• Do not use landscape lighting to light up trees or gardens where birds may be resting.
• Close blinds at night to reduce the amount of light being emitted from windows.
• Use lighting shields to direct light downwards and to avoid light shining into the sky or trees.
• Use motion detectors and sensors so lights are only on when you need them.
• Use desk lamps or task lighting rather than overhead lights. 
• Avoid floodlights.
• Dim exterior and decorative lighting.

What species of birds migrate through Texas? 

Texas Parks and Wildlife notes these birds fly over Texas during peak migration season: 

• American Golden-Plover
• Chimney Swift
• Ruby-throated Hummingbird
• Purple Martin
• Barn Swallow
• Northern Parula
• Black-throated
• Green Warbler
• Yellow-throated Warbler
• Black-and-white Warbler
• Hudsonian Godwit
• Buff-breasted Sandpiper
• Yellow-billed Cuckoo
• Golden-winged Warbler
• Cerulean Warbler
• Olive-sided Flycatcher
• Eastern Wood-Pewee
• "Traill's" Flycatcher
• Magnolia Warbler
• Blackburnian Warbler
• Bay-breasted Warbler

This article originally appeared on Austin American-Statesman: Millions of birds may die while migrating through Texas. Here's why and how to help

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This Lava Tube in Saudi Arabia Has Been a Human Refuge for 7,000 Years

Ancient humans left behind numerous archaeological traces in the cavern, and scientists say there may be thousands more like it on the Arabian Peninsula to study.

By Robin George Andrews

When ancient humans pushed into the Arabian Peninsula, they found a world marked by magma. Swaths of it once erupted from volcanoes, leaving a landscape of craters and frozen lava flows. Many of these seemingly otherworldly volcanic fields are adorned with archaeological remains — from small dwellings to colossal animal-corralling structures called kites — that date back millenniums.

Little is known about the identities and lives of those humans. But a study published Wednesday in the journal PLOS One has revealed that their occupation of this volcanic realm extended underground. Archaeologists at a site in northwestern Saudi Arabia have excavated a lava tube — the naturally hollowed-out subterranean remnant of a lava flow.

In this lava tube, named Umm Jirsan and the first in Saudi Arabia to be excavated, they uncovered stone tool fragments, animal remains and human bones, the oldest of which were close to 7,000 years old.

“This is really the first clear evidence of people occupying these caves,” said Mathew Stewart , a paleontologist at Griffith University in Australia who is one of the study’s authors.

Umm Jirsan’s tunnels have a combined length of almost 5,000 feet, and only small sections have been examined. Rather than as a permanent habitat, early humans probably used this volcanic cave as a way station during migrations between oases. “Umm Jirsan would have offered a really nice place of refuge,” from shifting and often extreme climatic conditions, Dr. Stewart said.

With thousands of additional volcanic caves like Umm Jirsan across Saudi Arabia, the new study shows that they “hold huge promise” for understanding the migrations of early humans, Dr. Stewart said.

The Arabian Peninsula has been a site of human migration and occupation for hundreds of thousands of years. In extensive surveys in recent years, scientists have spied millions of archaeological features (like lakeside hearths) and structures (like tombs and ritual gathering sites) that those people left behind. “On the volcanoes themselves, there’s archaeology,” said Melissa Kennedy , who is an archaeologist at the University of Sydney not involved with the new work. Many such sites date back to times when stone tools were in vogue.

The timing and nature of the region’s various occupations are still poorly understood. One issue is that desert heat and winds degrade bones and other organic material. But Saudi geologists, who had comprehensively mapped their country’s lava tubes, had noted the presence of archaeological remains, suggesting that these caves may better preserve fragile matter.

To test that notion, in 2019, Dr. Stewart’s team went to Umm Jirsan to conduct the first archaeological excavation of an Arabian Peninsula lava tube. An earlier study based on that expedition revealed that hyenas had used it as a den and left behind remains of birds, hare, gazelle and camels (all possibly prey). Two human skull fragments were also found.

“Hyenas were robbing graves,” Dr. Stewart said. But aside from these scavengings, were there more human remains in the lava tube?

The team’s new study reveals an abundance of evidence of human sojourns elsewhere in the cave: obsidian flakes (fragments of sharp volcanic rock shards used in tools), additional human remains and many more animal bones. Various dating techniques suggest that humans intermittently occupied Umm Jirsan over a period of at least 7,000 years, including recent centuries.

They brought animals with them, a notion supported not just by the remnants at the site. The team discovered 16 rock art panels in the entrance to another lava tube nearby. Some show people herding cattle, sheep and goats, sometimes with the aid of dogs; others depict people hunting gazelles and possibly ibex.

The current crop of evidence paints a vivid picture of the past, but much of the lava tube remains unstudied. “There could be some really spectacular stuff in there,” said Hugh Thomas , an archaeologist at the University of Sydney who was not involved with the new work.

But it’s already clear that Saudi Arabia’s lava tubes offer a new way “of looking through time and through space,” said Michael Petraglia , who is the director of the Australian Research Centre for Human Evolution at Griffith University and an author of the new study. Each could be an unopened window into the lives of humanity’s ancestors.

“This cave is just the beginning,” he said.