Migration Of Birds Essay

Bird Migration: Facts

Where Are They Going?

Have you ever seen flocks of geese flying south in the fall? Have you heard them honking? Have you wondered why they are flying in a formation that looks like a “V”? Have you wondered where they are going? They, like many other birds, are migrating.

The word migration comes from the Latin word, migratus, which means “to change.” The word has special meaning when it refers to animals. Migration is the movement of an animal from one region, or habitat, to another. This happens at regular periods of time, and during a particular season. Animals migrate in order to breed, grow, find food or avoid cold weather. For birds, this occurs twice a year. They migrate in the spring and again in the fall.

What Makes A Bird, A Bird?

All bird species have feathers. There are several other characteristics that birds share, but feathers are the only characteristic completely unique to birds. Many might say that it is flight that makes birds special, but did you know that not all birds fly? Emu, kiwi, cassowary, penguin, ostrich and rhea are birds that don't fly. Some birds swim, like the penguin, which does its flying underwater. Learn all about flightless birds.

Birds have many interesting adaptations to benefit their life in the air. They have lightweight, yet strong, bones and beaks, which are adaptations to reduce weight for flying. Birds have incredible eyes, ears, feet, and nests. We enjoy listening to the songs of birds. Discover more about birds.

Why Do Birds Migrate?

Birds seek out places that have warmth, food and are safe for breeding. In the Southern Hemisphere, especially in the tropical climates, it is warm enough — since there is little change in the length of the days from month to month — that birds are able to find an adequate food supply year round. The steady daylight gives birds plenty of time to eat each day, so they don't need to go someplace else to find food.

Conditions are different in Northern Hemisphere countries like the United States and Canada. During the long days of the northern summer, birds have more hours to feed their young on the abundant insect population. But as the days shorten during autumn and food supplies become scarce, some birds migrate south.

Not all birds migrate. There are some species that manage to survive winter while staying in the Northern Hemisphere. Typically, familiar species such pigeons, crows, ravens and blackbirds stay put all year round.

There are 4 kinds of migrating birds:

  • Permanent residents are non-migrating birds who remain in their home areas all year round.
  • Summer residents are migratory birds that move north in the spring, nest during the summer, and return south in the fall.
  • Winter residents are migratory birds who fly south for the winter.
  • Transients are migratory species who nest farther north than our neighborhoods, but who winter farther south. We only see transients as they are passing through.

When Do Birds Migrate?

Each species migrates at a certain time of year and time of day. Some are very irregular in their migration patterns. Some species start their migration south in early July, and some don't migrate until the weather gets too harsh or food becomes unavailable later in the fall. Experiments show that the length of the day stimulates migration. In spring, you might see migrating birds as early as January in Florida!

Where Do Birds Go?

Many species migrate very long distances. The most common pattern is that birds migrate to the temperate or arctic Northern Hemisphere to breed in the summer and migrate south to warmer regions for the winter. There are four main flyways, or migration routes, in North America that most birds follow between their summer and winter locations.

Migrating birds follow certain traditional migratory routes and pass through at predictable times. These routes tend to avoid land forms that might block their way, such as mountains, or water. For soaring birds, such as ospreys, eagles, vultures, and hawks these routes follow paths that take them by areas that generate hot air funnels to rise up from the land. They use this hot air, known as thermals, to soar. By spiraling up a thermal and gliding down to the next one, they save energy needed for long journeys.

How Do They Keep Going?

Some birds eat along the route, but some birds eat more just before migration and store a special, high-energy fat in their bodies. This is necessary because some might not eat for several weeks as they migrate.

Most birds that require food during the trip fly by night in small flocks. This allows them to eat during the day, and avoid some predators.

How Do Birds Find Their Way?

Navigation is complicated because it requires that birds know three things: their current location, their destination, and the direction they must take to get their destination.

Some birds use the sun and the stars to navigate. Some also use the sighting of landmarks like rivers, mountains or coastlines. Some might use smell, while some might follow other birds in the flock. But birds can still navigate on cloudy days and fly across the ocean where there are no landmarks. So how can they do this?

Scientists have come to believe that birds monitor the earth's magnetic field using tiny grains of a mineral called magnetite that are located in their beaks. The iron-containing mineral might act like a compass. Other scientists think that the birds can actually see the magnetic field with their eyes. Not all is known about how birds find their way, but they probably use more than one method. Learn more about bird navigation.

So Why Do They Fly In A V Formation?

Flying in that V formation is not an accident. Large birds such as geese and ducks fly in this formation to reduce the effect of friction on their wings. This allows the birds to fly further and more efficiently than a bird flying alone by itself.

There is a 70% increase in efficiency when flying in V formation. The lead bird and the last birds flying farthest back in the V work the hardest, while the birds in between benefit from the flapping motion of the other birds.

In addition to improving their flight, this formation also benefits the communication among the birds. This formation places the birds close together, allowing them to hear and see one another. They honk information to each other (or quack or whatever sound they make) and can watch over one another to keep together.

What Are The Dangers Of Migration?

Sometimes birds must fly across harsh habitats such as deserts, where there is little water, or oceans, where there is no place to land and little food to eat.

Even if they find food and water, they must land to be able to take advantage of the opportunity. This means putting themselves in danger of becoming someone else's food.

There can be many predators along the migration route. Depending on the size of the birds, they can find themselves in danger from cougars, foxes, wolves, humans, or many others. Some birds can actually be attacked by larger birds while in flight. Sometimes stormy weather may make the trip difficult and cause death in severe cases. And occasionally birds have been known to fly into the path of airplanes. This can be dangerous to both bird and airplane.

How Do Ornithologists Study Birds and Migration?


Bird banding or ringing is one method used to study wild birds. Scientists attach a small, individually numbered metal or plastic ring to a bird's leg or wing. They also use special nets known as mist nets as a way to capture birds. This way they can capture and re-capture the same individual bird and measure and weigh it and gather other important information over time.

The Pelican Network has some excellent photos of that process. Sometimes scientists use satellite tracking to follow birds on their migration routes. The U.S. Geological Survey offers a brief description of this technology.

Birdwatching

Birdwatching is the second largest hobby (gardening is the first) in North America with over 31 million participants. People all over the world follow and watch birds and their behavior. They learn to identify birds by their song and by their behavior. People do it for fun, but if you study birds as a career, you are an ornithologist. Learn about birdwatching adventures you can have at Visit Idaho or BirdingPal.

You might want to explore another Science Trek topic and become familiar with Birds of Prey.

If you love birds and think that this might lead you to a future career, take a peek at the job of an ornithologist at Seattle's Burke Museum.

Fascinating Facts


The Arctic Tern has the longest known migration route. It flies about 22,000 miles each year between its breeding grounds in the high Arctic and its winter grounds in the Antarctic.

 

The swallows of Capistrano have been known for their special migration habits. Cliff swallows flew to the San Juan Capistrano Mission in California and arrived every year on March 19th. On that date since the mission was built in the late 1700's, people have watched as hundreds of birds arrived on their migration from Argentina. Then they left again on October 23rd just as they came in — all together as a flock. The swallows probably came to this general area even before the mission was built, but no one was there to see it happen. In recent years the birds have stopped this annual trip. Scientists are trying to determine what has made them miss their appointment.

Birds can fly at speeds ranging from 20 to 50 miles per hour. Larger birds fly faster than smaller birds. If the flock flies for 10 hours a day, then they can fly about 400 miles a day!

Radar studies show that most flight occurs at less than 10,000 feet, but some birds have been recorded flying as high as 27,000 feet! Birds on long-distance migrations fly at higher altitudes than those who fly short-distances.

Previous (Bird)

Next (Birefringence)

Bird migration refers to the regular (and often seasonal) journeys to and from a given area undertaken by all or part of a bird population. Not all bird species (or even populations within the same species) are migratory. In contrast to more irregular movements such as emigration, nomadism, and invasion, which are made in response to changes in food availability, habitat, or weather, bird migration is marked by its cyclical pattern.

The most common pattern among the migratory birds of Europe and North America involves flying north to breed in the temperate or arctic summer and returning to wintering grounds in warmer regions to the south. However, other patterns of migration have been observed: In tropical regions, for example, some species migrate in response to the cycle of wet and dry seasons. In mountainous areas, like the Himalayas, vertical movements may occur from higher breeding grounds to lower altitudes with less exposure to harsh winter weather.

The primary advantage of migration is energetic. In the Northern Hemisphere, the long days of summer provide greater opportunities for breeding birds to feed their young. As the days shorten in autumn, the birds return to warmer regions where the available food supply varies little with the season. Migratory birds have evolved to undertake long-distance flights efficiently, and they undergo physiological changes (such as an accumulation of fat stores) prior to migration that minimize the energetic cost of flight.

Migrations typically occur along established routes called "flyways." The migrating species often return to the area of their birth to breed. The birds are guided by innate behaviors (including hormonal signals) that enable them to know when to depart and that orient them toward a specific location over long distances. However, they also remain flexible to environmental conditions, such as food supply and temperature, which may fluctuate yearly.

Bird migration has larger ecological implications that underscore the interconnectedness of life: Migratory cycles are closely attuned to seasonal food productivity cycles, which leads to a mutual gain for both the migrating species and the ecosystems in which they participate. Migratory birds are able to settle in areas where life is not tenable year-round, while the food resources of some regions would not be adequately utilized without the seasonal presence of migrating populations.

Bird species have diverse modes of migration

The varied patterns and modes of bird migration may be understood as adaptations. In fact, migration itself has conferred an advantage to only certain bird species, while not evolving in other species that remain resident, or sedentary, year-round. Whether a particular species migrates depends on a number of factors. The climate of the breeding area is important, as few species can cope with the harsh winters of inland Canada or northern Eurasia. The nature of the staple food is also significant. Most specialist insect eaters that breed outside the tropics are long-distance migrants, and have little choice but to head south in winter.

Even within a given species, not all populations may be migratory—a phenomenon termed "partial migration." Partial migration is very common in the southern continents; in Australia, 32 percent of passerine (perching) species and 44 percent of non-passerine birds were found to be partially migratory (Chan 2001). Moreover, within a specific population, there can be different patterns of timing and migration based on characteristics like age and sex. For example, only the female Chaffinches of Scandinavia migrate, while the males stay resident, a migratory pattern that has given rise to the name coelebs, meaning "bachelor."

Migrations vary widely in terms of the distance traveled. Short-distance passerine migrants, such as the waxwings, are effectively moving in response to winter weather, rather than enhanced breeding opportunities. Some Alaskan Bar-tailed Godwits have the longest non-stop flight of any migrant, flying 11,000 kilometers (km) to their New Zealand non-breeding areas. Prior to migration, 55 percent of their bodyweight is stored fat to fuel this uninterrupted journey. The Arctic Tern has the longest-distance migration of any bird, and sees more daylight than any other, moving from its Arctic breeding grounds to the Antarctic wintering areas. One Arctic Tern, ringed (banded) as a chick on the Farne Islands off the British east coast, reached Melbourne, Australia in just three months from fledging, a sea journey of over 22,000km (14,000 miles).

Migrations may be diurnal (occurring during the day) or nocturnal. Many of the smaller insectivorous birds, including the warblers, hummingbirds, and flycatchers, are nocturnal migrants. By migrating at night, they minimize the risk of predation, and avoid the overheating that could result from the energy expended to fly such long distances. Those smaller species that migrate during the day tend to be those making movements that are relatively short and weather-driven, like the larks and finches, or that can feed on the wing, like swallows and swifts.

The altitude at which birds fly during migration also varies. In general, migratory birds fly at low altitude, with most migrations in the range of 500-2000 feet. However, an expedition to Mt. Everest found skeletons of Pintail and Black-tailed Godwit at 16,400 feet on the Khumbu Glacier (Geroudet 1995). Bar-headed Geese have been seen flying over the highest peaks of the Himalayas above 29,000 feet even when low passes of 10,000 feet were nearby (Swan 1970).

Migratory birds follow established routes

Migration often is concentrated along well-established routes known as flyways, which are shaped by geographical, ecological, and even meteorological factors. Flyways typically follow mountain ranges or coastlines, and may take advantage of updrafts and other wind patterns, or avoid geographical barriers, such as (in the case of land birds) large stretches of open water.

Theoretical analyses, summarized by Alerstam (2001), show that detours that increase flight distance by up to 20 percent will often be adaptive on aerodynamic grounds—a bird that loads itself with food in order to cross a long barrier flies less efficiently. However, some species show circuitous migratory routes that reflect historical range expansions and are far from optimal in ecological terms. An example is the migration of continental populations of Swainson's Thrush, which fly far east across North America before turning south via Florida to reach northern South America; this route is believed to be the consequence of a range expansion that occurred about 10,000 years ago. Detours may also be caused by differential wind conditions, predation risk, or other factors.

Some large broad-winged birds rely on thermal columns of rising hot air to enable them to soar. These include many birds of prey, such as vultures, eagles, and buzzards, as well as storks. Migratory species in these groups have great difficulty crossing large bodies of water, since thermals form over land only. The Mediterranean and other seas therefore present a major obstacle to soaring birds, which are forced to cross at the narrowest points. Massive numbers of large raptors and storks pass through areas such as Gibraltar, Falsterbo, and the Bosphorus at migration times.

By following established routes, some species risk predation during periods of peak migration. For example, the Eleonora's Falcon, which breeds on Mediterranean islands, has a very late breeding season, coordinated with the autumn passage of southbound passerine migrants, which it feeds to its young. A similar strategy is adopted by the Greater Noctule bat, which preys on nocturnal passerine migrants (Dondini et al. 2000; Popa-Lisseanu et al. 2007; Ibáñez et al. 2001).

Despite the genetic and environmental factors that guide them along specific routes, migrating birds can still lose their way. In a phenomenon known as the "spring overshoot," birds returning to their breeding areas overshoot their destination and end up further north than intended. "Drift migrations" of birds blown off course by the wind can result in "falls" of large numbers of migrants at coastal sites.

Patterns of migration

Many migratory European and North American species fly south in winter

The distance traveled by migratory birds of the Northern Hemisphere varies widely. Some European birds, such as the insect-eating warblers, flycatchers, and wagtails, as well as swallows and storks, migrate to areas of Africa south of the Sahara. North American birds, like the ruby-throated hummingbird, which breeds in southern Canada, may travel as far south as Panama for the winter; others, like the American robin and several species of grackles, winter in the states along the Gulf Coast.

Many northern-breeding ducks, geese, and swans are also long-distance migrants, but need only to move from their Arctic breeding grounds far enough south to escape frozen waters. Most Holarctic wildfowl species remain in the Northern hemisphere, but in countries with milder climates. For example, the Pink-footed Goose migrates from Iceland to Britain and neighboring countries.

A similar situation occurs with waders (called "shorebirds" in North America). Many species, such as the Dunlin and Western Sandpiper, undertake long movements from their Arctic breeding grounds to warmer locations in the same hemisphere, while others, such as the Semipalmated Sandpiper, travel greater distances to the tropics.

Some Southern species winter in northern areas

Although bird migrations in the Southern Hemisphere are less well-observed than Northern ones (in part because the largely uninterrupted expanses of land mass and ocean tend not to funnel migrations into narrow pathways), many species do in fact breed in the temperate regions of the Southern Hemisphere and winter further north in the tropics. The southern African Greater Striped Swallow, the Australian Satin Flycatcher, Dollarbird, and Rainbow Bee-eater, for example, winter well north of their breeding range. A few seabirds, such as Wilson's Petrels and Great Shearwaters, breed in the Southern Hemisphere and migrate north in the southern winter.

Two types of migrating seabirds

Seabird migration may be characterized as "coastal," with species following along the continental shelf, or "pelagic," with species ranging across the open sea. The former category includes birds such as the guillemots, auks, cormorants, gannets, and gulls, which are all found along the seashore.

The most pelagic species, mainly in the "tubenose" order Procellariiformes (petrels and albatrosses), are great wanderers. The albatrosses of the southern oceans may circle the globe as they ride the "roaring forties" outside the breeding season. Many are also among the longest-distance migrants; Sooty Shearwaters nesting on the Falkland Islands migrate 14,000km (9,000 miles) between the breeding colony and the North Atlantic Ocean off Norway. As they are long-lived birds, they may cover enormous distances during their lives; one record-breaking Manx Shearwater is calculated to have flown 8 million kilometers (5 million miles) during its lifespan of over 50 years.

Tropical migration: Wet and dry seasons

In the tropics, there is little variation in the length of day throughout the year, and it is always warm enough for an adequate food supply. Apart from the seasonal movements of Northern Hemisphere wintering species, most species are in the broadest sense resident. There are a few species, notably cuckoos, which are genuine long-distance migrants within the tropics. An example is the Lesser Cuckoo, which breeds in India and spends the non-breeding season in Africa.

However, some tropical species undergo movements of varying distances depending on rainfall. Many tropical regions have cycles of wet and dry seasons, the monsoons of India being perhaps the best-known example. An example of a bird whose distribution is rain associated is the Woodland Kingfisher of west Africa.

Vertical movements

Some migrations involve changes in altitude, as species move vertically from higher breeding zones to the foothills or plains during unfavorable weather. For example, mountain and moorland breeders, such as the Wallcreeper and White-throated Dipper, may move altitudinally to escape the cold higher ground. In the Himalayas and Andes, there are also seasonal vertical movements in many species, and others may undertake migrations of considerable length. The Himalayan Kashmir Flycatcher and Pied Thrush both move as far south as the highlands of Sri Lanka.

Pantanal: Example of region of southern, northern, and vertical movements

The Pantanal, a semitropical region contained within the Upper Paraguay River Basin of Brazil, Paraguay, and Bolivia, and the world's largest wetland system, is an important migratory bird stopover point and wintering ground. It is used by birds from three major migratory flyways—bringing ospreys from the Nearctic latitudes to the north, woodstorks from the Argentine pampas to the south, and flycatchers from the Andes to the west (Eckstrom 1996). Included in the bird fauna of the Pantanal are such North American migratory birds as the upland sandpiper (Bartramia longicauda), the American golden plover (Pluvialis dominica) and the black-necked stilt (Himantopus himantopus) (Swarts 2000).

Signals

The timing and response of migration are in large part genetically controlled. In contrast, the ability of migratory birds to navigate and orient themselves during migration is a much more complex phenomenon that may include both endogenous (internal) programs as well as learned behavior (Helm and Gwinner 2006).

Physiological changes prepare migratory birds for flight

The primary environmental cue for migration is change in day length, which is related to hormonal changes in migratory birds. The pituitary gland (an endocrine gland that controls the release of hormonal stimuli) prepares birds for flight by initiating physiological changes. However, certain ecological conditions, such as changes in temperature and weather conditions, are necessary to trigger flight.

In the period before migration, many birds display higher activity known as zugunruhe, a German term meaning "migratory restlessness." The occurrence of zugunruhe even in cage-raised birds with no environmental cues (e.g., shortening of day and falling temperature) has pointed to the role of endogenous programming in controlling bird migrations.

Birds preparing for migration also undergo metabolic changes such as increased fat deposition, which enables long-distance migrants, such as the ruby-throated hummingbird, to conserve muscle protein, enabling them to make their arduous, 2,400 kilometer flight.

Orientation and navigation during flight draw on multiple senses

The navigational abilities of migratory birds has been shown to be based on a combination of abilities, such as detecting magnetic fields, using visual landmarks, and sensing olfactory cues (Wallraff 2005). Many birds have been demonstrated to have a "compass sense;" i.e., they are able to fly in a particular constant direction, regardless of their release point. An internal clock mechanism enables birds to use the sun as a point of orientation, determining the angle of the sun above the horizon. Nocturnal migrants may also use the stars to get their bearings.

However, the ability of birds to navigate during migrations cannot be fully explained by endogenous programming, even with the help of responses to environmental cues. The ability to successfully perform long-distance migrations can probably only be fully explained with an accounting for the cognitive ability of the birds to recognize habitats and form mental maps. As the circannual patterns indicate, there is a strong genetic component to migration in terms of timing and route, but this may be modified by environmental influences.

Historical background and modern study techniques

Although bird migrations have been observed for thousands of years, it was not until the early nineteenth century that migration was accepted as an explanation for the winter disappearance of birds from northern climes (Lincoln 1979).

Bird migration has been studied using a variety of techniques, of which ringing is the oldest. Color marking, use of radar, satellite tracking, and stable Hydrogen and Strontium isotopes are some of the other techniques being used today to study the migration of birds (Font et al. 2007). To identify migration intensity, one contemporary approach makes use of upward pointing microphones to record the contact calls of overflying flocks; these calls are then analyzed in a laboratory to measure time, frequency, and species (Farnsworth et al. 2004).

References

  • Chan, K. 2001. Partial migration in Australian landbirds: A review. Emu 101(4): 281-92.
  • Dondini, G., and S. Vergari. 2000. Carnivory in the greater noctule bat (Nyctalus lasiopterus) in Italy. Journal of Zoology 251: 233-6.
  • Dorst, J. 1963. The Migration of Birds. Boston: Houghton Mifflin.
  • Eastwood, E., and G. C. Rider. 1965. Some radar measurements of the altitude of bird flight. Brit Birds 58: 393-426.
  • Eckstrom, C. K. 1996. A wilderness of water: The Pantanal. Audubon 98(2): 54-65.
  • Farnsworth, A., S. A. Gauthreaux, and D. van Blaricom. 2004. A comparison of nocturnal call counts of migrating birds and reflectivity measurements on Doppler radar.Journal of Avian Biology 35: 365-9. Retrieved August 16, 2007.
  • Font, L., M. Geoff, D. Nowell, G. Pearson, C. J. Ottley, and S.G. Willis. 2007. Sr isotope analysis of bird feathers by TIMS: A tool to trace bird migration paths and breeding sites. J Anal At Spectrom 22: 513.
  • Geroudet, P. 1954. Des oiseaux migrateurs trouves sur la glacier de Khumbu dans l'Himalaya. Nos Oiseaux 22: 254.
  • Helm, B., and E. Gwinner. 2006. Migratory restlessness in an Equatorial nonmigratory bird.PLoS Biol 4(4): e110. Retrieved August 16, 2007.
  • Ibáñez, C., J. Juste, J. L. García-Mudarra, and P. T. Agirre-Mendi. 2001. Bat predation on nocturnally migrating birds. PNAS 98: 9700-9702.
  • Liechti, F. 1996. Instructions to count nocturnal bird migration by watching the full moon. Schweizerische Vogelwarte CH-6204. Sempach, Switzerland.
  • Lincoln, F. C. 1979. Migration of birds.Fish and Wildlife Service, Circular 16. Retrieved August 16, 2007.
  • Lowery, G.H. 1951. A Quantitative Study of the Nocturnal Migration of Birds. Lawrence, KS: University of Kansas Publications.
  • Popa-Lisseanu, A. G., A. Delgado-Huertas, M. G. Forero, A. Rodriguez, R. Arlettaz, and C. Ibanez. 2007. Bats' conquest of a formidable foraging niche: The myriads of nocturnally migrating songbirds.PLoS ONE 2(2): e205. Retrieved August 16, 2007.
  • Rattenborg, N. C., B. H. Mandt, W. H., Obermeyer, P. J. Winsauer, and R. Huber. 2004. Migratory sleeplessness in the white-crowned sparrow (Zonotrichia leucophrys gambelii).PLoS Biol 2(7): e212. Retrieved August 16, 2007.
  • Schmaljohann, H., L. Liechti, and B. Bruderer. 2007. Songbird migration across the Sahara: The non-stop hypothesis rejected!Proc Biol Sci 274(1610): 735-9. Retrieved August 16, 2007.
  • Swan, L. W. 1970. Goose of the Himalayas. Nat Hist 79(10): 68-75. Retrieved August 16, 2007.
  • Swarts, F. A. 2000. The Pantanal in the 21st Century: For the planet's largest wetland, an uncertain future. In F. A. Swarts (ed.) The Pantanal. St. Paul, MN: Paragon House. ISBN 1557787913
  • Wallraff, H. G. 2005. Avian Navigation: Pigeon Homing as a Paradigm. New York, NY: Springer. ISBN 3540223851
  • Williams, G. G. 1950. Weather and spring migration. Auk 67: 52-65.
  • Wiltschko, W., U. Munro, H. Ford, and R. Wiltschko. 2006. Bird navigation: What type of information does the magnetite-based receiver provide? Proc R Soc B 273: 2815-20.

Further reading

  • Alerstam, T. 2001. Detours in bird migration. Journal of Theoretical Biology 209: 319-331.
  • Berthold, P. 2001. Bird Migration: A General Survey, 2nd ed. New York: Oxford University Press. ISBN 0198507879
  • Dingle, H. 1996. Migration: The Biology of Life on The Move. New York: Oxford University Press. ISBN 0195089626
  • Weidensaul, S. 1999. Living On the Wind: Across the Hemisphere With Migratory Birds. Vancouver, BC: Douglas and McIntyre. ISBN 0865475431

External links

All links retrieved June 10, 2016.


editBirds
Anatomy: Anatomy - Skeleton - Flight - Eggs - Feathers - Plumage
Evolution and extinction. Evolution - Archaeopteryx - Hybridisation - Late Quaternary prehistoric birds - Fossils - Taxonomy - Extinction
Behaviour: Singing - Intelligence - Migration - Reproduction- Brood parasites
Bird types: Seabirds - Shorebirds - Waterbirds - Song birds - Raptors - Poultry
Bird lists:Familes and orders - Lists by region
Birds and Humans: Ringing - Ornithology - Birdwatching - Birdfeeding - Conservation - Aviculture

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A flock of Barnacle Geese during autumn migration.
The fat stores of the ruby-throated hummingbird increase prior to migration.
Arctic Terns migrate vast distances.
The Cedar Waxwing is a short-distance migrant.
A Griffon Vulture soaring. The migratory routes of vultures and many other birds of prey take advantage of ecological features like thermal columns to power their flight.
The Northern Pintail breeds in the northern areas of Europe and Asia and across most of Canada, Alaska and the mid-western United States; it winters as far south as the Equator.
The Australian Rainbow Bee-eater winters north of its breeding range.
The Woodland Kingfisher migrates into the equatorial zone during the dry season.

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