The Basics of Bird Migration: How, Why, When, and Where

Latest update April 2026; originally published January 2007. Lots of animals, from whales to wildebeest, make long annual migrations. But birds do it in the most spectacular fashion. They move... Read more »

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Migration Basics | Navigation | Flyways | Evolution of Migration

Latest update April 2026; originally published January 2007.

Lots of animals, from whales to wildebeest, make long annual migrations. But birds do it in the most spectacular fashion. They move farther, faster, and in greater numbers than any other animals. On a single autumn night with favorable winds, there can be more than 1 billion birds in the air over the United States alone.

Some birds travel tremendous distances: Arctic Terns and Sooty Shearwaters fly more than 50,000 km (31,000 miles) in a single year. Bar-tailed Godwits depart Alaska at the end of summer and fly nonstop for 8 days over the Pacific Ocean, landing in New Zealand. Even little songbirds and tiny hummingbirds routinely fly 1,100 km (700 miles) across the Gulf of Mexico each year. In all, more than 300 North American bird species are long-distance migrants.

Although some birds migrate during daytime, including raptors, waterfowl, and swallows, most birds migrate at night, when atmospheric conditions are calmer and there are fewer predators about. So how do birds travel such long distances, in the dark, and find their way to the exact same patch of wintering or breeding habitat each year? Let’s explore.

It can be hard to grasp the sheer scale of migration: birds are tiny but so numerous, and they move across such vast distances. This visualization depicts the staggered movement of millions of birds, representing 15 species, during four months in spring.

Why Do Birds Migrate?

Migration allows birds to take advantage of good conditions in different locations at different times of year.

Birds typically migrate to take advantage of these three resources:

Food. Birds that nest in the Northern Hemisphere tend to migrate northward in the spring to take advantage of a few months of plenty, fed by burgeoning insect populations and budding plants.
Breeding Sites. The vast boreal forests and open tundra of the Arctic provide huge expanses for shorebirds and songbirds to nest in, compared with the crowded forests of the tropics—making it worth the long journey.
Daylight. Near the equator, daytime is about 12 hours long all year. By traveling to nearer the poles, birds can get much longer daylight, just when they need it most for raising their young. The extra daylight also fuels the abundant plant, plankton, and insect booms that create such a plentiful food supply.

Perhaps surprisingly, weather is not on this list. Escaping cold temperatures is not itself a major factor that drives birds to migrate, since many species, even hummingbirds, can withstand freezing temperatures as long as an adequate supply of food is available.

Show Transcript

[soundscape of birds calling]
[text on screen: Ask an Expert: Top Bird Migration Questions. Dr. Kevin J. McGowan, Bird Academy Senior Course Designer. Highlights from a webinar recorded in Sept 2023. Image of two Sandhill Cranes in a marsh. Logo: Cornell Lab]
[text on screen: Why do birds migrate?]
People should know that not all birds migrate.
Some birds just stay in the same place all year long. So if we think about the birds up in the boreal forest, the chickadees stay there all year round. They can find, believe it or not, insect eggs and little things like that in the bark, that they can find enough food to keep them, keep them going during the winter. But a lot of the other birds feed on flying insects or moving insects, and there aren’t too many of those, up in Canada in the wintertime, so they have to go somewhere else to find food. Migration is almost always about finding food. It’s not to get out of the cold because birds can survive cold. But there are certain inhospitable places that they need to leave. But it’s almost always about food.
[text on screen: What prompts birds to start migrating?]
Well, the thing that starts bird migration usually is a change in daylight and what that does is that starts this sort of, the, the proximate mechanism that gets the birds brains changing, different hormones being produced, and the birds can sense even very small changes in daylight length. There’s this cool term that’s in German called Zugunruhe and that means migratory restlessness.
[text on screen: Zugunruhe. Migratory Restlessness]
And so we can you can watch this. And it’s been well studied in birds that if you keep them in captivity, as the light changes, as the days get smaller or longer, they start to get antsy and they just kind of move around in their cages and they just want to go somewhere. And it’s just this need to, to go further, to go further, go south, go south, go down, you know.
[text on screen: How variable is migration timing?]
In fact it’s actually fairly rigorous in some species. It’s very, very predictable. Like when Red-winged Blackbirds turn up in central New York, is is always within a two week period. And so some of these things are very precise. However, migration on, you know, for an individual bird depends on the, circumstances that that bird is in. And that includes changes in weather and, and local conditions and stuff like that. So there’s always that sort of fine tuning. So it’s never precisely the same.
[text on screen: Do adult and juvenile birds migrate together?]
Yeah, that’s an interesting thing about migration is we tend to think, oh well, yeah, they just go—But they don’t There are different… different… the sexes do different things. And the juveniles do different things. And typically what you see going first are the males, the breeding males of a lot of different birds leave the breeding grounds before the females or the juveniles do. And then as a… again, as a general rule of thumb the adults leave first and then the juveniles leave later. And it may be they just need a longer time to fatten up, to migrate. But that’s very a very predictable pattern that we see
[text on screen: What’s the best time of day to migrate?]
[image: map of continental United States in purple, orange, and yellow against a black background, colors indicate predicted strength of bird migration. Text on screen: Migration intensity scale: white = High; yellow to orange = Medium; purple = Low; dark = None. 378 million birds predicted. Logo: BirdCast]
Different birds do migrate at different times of the day. And to, a lot of people are surprised to know that the the bulk of migration happens at night, that most birds fly at night. And there’s several reasons for this. One is that they, you know, there are fewer predators being able to catch you at night. You can’t really forage that much, so you might as well fly.
[Image: graphic of a flying Yellow Warbler against a globe depicting lines of magnetic force]
When there’s not enough light to see very well, birds can actually turn on a different sense and see the magnetic fields of the earth. And so they can tell north and south, because they can see the magnetic fields. I read that news and it’s like, oh, that’s why they fly at night is because then they can see. And that does seem to be the consensus is that, a lot of the nighttime flying, is because that allows them to use their magnetic sense to detect north and south.
[text on screen: How can people help migrating birds?]
Well, hummingbird feeders, the hummingbirds really like hummingbird feeders, and you won’t make them stop migrating, and stick with it and stick with your feeder till it gets cold. They’re not going to do that. But they will use it as a source of, cheap energy that they can put on and, and, help them along their way. Suet for some of the other birds is good. The other thing to do to help birds along during this is turn off your lights at night. That’s a big one. And of course, this really plays out in the cities. And, and there are the programs that people have, a number of organizations are working with, including the Cornell Lab of Ornithology, that are trying to encourage big cities to cut down on their light usage during peak migration time because birds get confused. And so turn off your lights at night, plant native plants, put up a hummingbird feeder. That doesn’t do it all. But there are a couple of tangible things that people can do.
[text on screen: Media Credits: Oregon soundscape by Todd Sanders / Macaulay Library; Sandhill Cranes by Dylan S. / Macaulay Library; Blaack-capped Chickadee by Nick Saunders / Macaulay Library; Tree Swallow by Blair Dudeck / Macaulay Library; Whimbrels by Matt Aeberhard / Macaulay Library; Red-winged Blackbirds by Ron Beurkert / Macaulay Library; American Avocets by Matt Zuro / Macaulay Library; BirdCast Migration Forecast 6 Sept 2024 / Cornell Lab and Colorado State University; Geomagnetic illustration by Jillian Ditner / Cornell Lab; Calliope Hummingbird by Joshua Glant / Macaulay Library; Nighttime view from space by NASA / JPL.]
[soundscape of bird calls ends]

End of Transcript

How Migration Evolved

It makes sense that migrating to places with abundant food, nest sites, and plenty of daylight would be beneficial. But how could birds gradually evolve the anatomy, physiology, and sense of direction needed to make such a long journey possible? Scientists have studied this question for many years, and this article covers some of the answers:

The Evolution of Bird Migration

Patterns of Bird Migration

Migration is any kind of regular, large-scale movement of animals. Over time, birds have evolved many patterns of migration. Some species move farther than others; some move with more or less regularity, giving rise to the following terms:

Permanent Residents

Do not migrate.

Short-Distance Migrants

Move short distances to avoid adverse weather.

Medium-Distance Migrants

Cover distances up to several hundred miles.

Long-Distance Migrants

Move thousands of miles, across continents.

Partial Migrants

Some individuals migrate while others remain resident year-round.

Elevational Migrants

Shift up or down slope to reach new resources without traveling far.

Irruptive Migrants

Move out of usual range, but only in some years.

Nomads

Unpredictable: move irregular distances at various seasons to find food.

How Do Birds Migrate?

Embarking on a long journey with just the right timing to match seasonal changes requires serious abilities: physical changes to the body; the ability to sense the time of year; and exquisite navigational senses.

Migration Timing

As migration approaches, birds shrink some of their organs and grow others to be in top flying condition. They also store energy as fat, to be metabolized during long flights with infrequent feeding stops.

Four cells of a cartoon. 1) Zugunruhe: migratory restlessness; when songbirds are ready to migrate, they literally cannot sit still. 2) Two birds talking. First: — *BirdWord cartoon* *by Rosemary Mosco.*

Birds use several cues to know when it’s time to depart. These include changes in day length, temperature, and food supplies. For centuries, people who kept cage birds noticed their birds repeatedly fluttering against their cage when it was time for migration. The birds flew toward one side in spring and the opposite side in autumn. German scientists called this zugunruhe (“migratory restlessness”); it neatly demonstrates that migrants have innate senses of timing and orientation.

navigation

Migrating birds can cover thousands of miles each year, often traveling the same course and arriving in the same patch of habitat year after year. Juvenile birds often migrate on their own, without any adults to show them the way, just a couple of months after they hatched. Somehow they can find their winter home despite never having seen it before.

Birds achieve such amazing navigational feats thanks to a combination of powerful senses. Cues they use include the position of the sun, and of sunset, the rotation of the stars, the Earth’s magnetic field, landmarks such as ridgelines and river valleys, and even their sense of smell.

Navigation: How Birds Find Their Way When They Migrate

Map of the Flyways — **Flyways of the World.** Shorebirds and waterfowl often migrate along established flyways. *Map courtesy of International Wader Study Group.*

Migration Flyways

Some species, particularly shorebirds, waterfowl, and cranes, follow preferred routes known as flyways on their annual migrations. These routes often include important staging grounds and stopover sites that provide food supplies critical to the birds’ survival. In 2015, scientists documented an additional flyway across the open Atlantic, used by at least 9 species including birds as small as the Blackpoll Warbler.

Raptors take different routes (often overland) that support their soaring flight style. Many songbirds don’t tend to use flyways at all, instead migrating in broad fronts across the landscape to take advantage of beneficial winds and food supplies.

The Flyways Birds Use to Migrate Across Continents

What Dangers Do Migrating Birds Face?

Embarking on a thousand-mile journey is dangerous and demanding. Birds face the tests of extreme physical exertion, lack of food along the way, unpredictable storms and headwinds, unfamiliar stopover habitat, predators, and the demands of navigating the correct course.

Increasingly, migrating birds also face human-made threats, particularly artificial lights and collision risks from windows, communication towers, and tall buildings.

For more about migration threats, as well as ways to keep birds safe:

Is Bird Migration Getting More Dangerous?

Bird Collision Prevention Alliance

How Can Birders Find Migrating Birds?

Two free tools are especially helpful for knowing where and when to look for migrating birds.

BirdCast uses weather radar to forecast how many birds will be on the move each night during spring and fall migration seasons across the U.S. Lower 48. At an even finer scale, BirdCast provides a dashboard you can check each day. It displays how many birds moved through in your county or state the previous night. It even suggests which species are most likely on the move. Here’s how to start using BirdCast for your daily birding intel:

How to Use BirdCast Maps and Dashboard to See Your Local Migration in Detail

eBird Maps

For longer-range planning, or whenever you’re curious, use weekly abundance maps from eBird Status and Trends. They show you where birds occur every week of the year, across their whole range, via a combination of eBird observations and habitat models. Search for a species and then click the “Weekly” tab to view the animation.

eBird Status and Trends

How Do People Study migration?

The sheer scale of bird migration has always made it hard for people to study. Birds are just too small, and travel too far and too fast. For decades, the best scientists could do was to put bands on birds’ legs and hope to recapture or resight them someday.

But a wave of technological innovation beginning in the 2010s has opened the floodgates to learning about where birds come from and where they go. New devices including lightweight transmitters, ingenious geolocators, tiny MOTUS tags that weigh less than 1 gram, and even genetic analyses. This Living Bird article covers some of the most exciting advances:

Migration Science Enters a Golden Age

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Ornithology: Comprehensive Bird Biology is a self-paced, college-level course that will transform your understanding of birds. Using this online course and the required textbook, you will gain in-depth knowledge of ornithology.