Bird Migration

Bird Migration Facts

Bird Migration [bûrd] [mī-'grā-shŭn]

The seasonal movement of birds from one region, or habitat, to another.

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.

A flock of geese flying at sunset

The word migration comes from the Latin word, migratus, which means “to change.” The word has a 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.

Parts of a bird identified

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, and 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.

Flock of geese flying at sunset

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 as pigeons, crows, ravens, and blackbirds stay put all year round.

Photo of a crow, a blackbird, and a pigeon

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?

A flock of ducks at sunset

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.

World map of the international migration zones

Migrating birds follow certain traditional migratory routes and pass through at predictable times. These routes tend to avoid landforms 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?

Two ducks eating on a grassy bank

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?

Several birds flying in front of the sun

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

Diagram of the Earth's magnetic fields

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.

Photo of birds migrating in the v formation

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 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.

Flock of migrating bird over a marsh

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 birds and airplanes.

How Do Ornithologists Study Birds and Migration?

Photo of a bird being banded as part of a study
Ornithologist attaching a band to a bird's leg

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, 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. NASA also explains how radar can teach us about bird migration.


Photo of a young bird watcher

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

Photo of pair of Artic terns
Artic terns

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.

A pair of nesting cliff swallows
Cliff swallows of Capistrano

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 appointments.

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.

Top 10 Questions

October 2009

Thanks to Jay Carlisle, Research Director, Idaho Bird Observatory; and Vicky Runnoe, Conservation Education Supervisor, Idaho Department of Fish and Game for the answers.

  1. What is the biggest bird?

    The Emu is probably the largest living bird. Emus are big in part because they don't fly. By not having wings, they can put on extra body weight. If they had to fly, they wouldn't be able to carry that weight. (From Kenton at Hayden Meadows Elementary School in Coeur d'Alene)

  2. How many birds migrate a year?

    Millions and millions of birds migrate every single year. It's hard to put a number on it. However, on each continent there are millions of birds migrating between the temperate and tropical zones every year. (From Grace in Mrs. Dransfield's class at Mary McPherson Elementary School in Meridian)

  3. How come some birds don't migrate?

    A lot of it depends on what they eat. If they eat insects and the insects die off during the winter months, they will need to migrate in order to eat. However, if they are a bird who eats foods that are around in the winter, like eating seeds for example, they won't have to migrate and will stay locally. (From Ben in Mrs. Dransfield's class at Mary McPherson Elementary School in Meridian)

  4. How do birds flap their wings so they don't get tired?

    Birds utilize oxygen very efficiently, allowing them to exercise (or flap their wings) more efficiently than we may be able to. Also, they store a lot of fat. Fat is their migratory fuel. This fuel allows them to keep going as if they had a battery. Some species can even fly for 72 hours continuously! However, scientists believe that there is evidence that birds really are tired when they land. Flapping a lot and being tired may go hand in hand. (From Jake in Mrs. Gris' class at Horizon Elementary School in Boise)

  5. Where do the birds from Idaho mostly go?

    It depends on the kind of bird. Our Mountain Bluebird migrates to the southern United States. The Osprey goes to South America. Central Mexico seems to be the area that hosts the highest number of Idaho species during the winter. (From Jenna in Mrs. Schweitzer's class at Riverside Elementary School in Boise)

  6. What birds are adapted to living in winter instead of going south?

    There are several birds that can live in winter weather conditions. For example, there are raptors, like the Red Tailed Hawk, that eat small mammals, and Bald Eagles that eat fish. These birds don't need to migrate as far. Black-capped Chickadees can switch their diet from eating more insects to eating more seeds and fruit, allowing them to stay here. Also Sparrows, the more common wintering birds in the Treasure Valley, feed on seeds through the winter. (From Elise in Mrs. Boyer's class at Mary Nelson Elementary School in Boise)

  7. Do birds carry diseases?

    Birds do carry diseases. Some areas have a higher prevalence of disease than others. In southwestern Idaho, we will see migrating birds carrying a virus called avian pox. This is not a fatal disease, but sometimes it can cause them to lose a toe or something like that. This is not a dangerous disease or really prevalent among the population, but there are other areas where a disease like that can be more dangerous to bird populations. (From Haven in Londeen's class at Christine Donnell Elementary School in Boise)

  8. Do owls migrate?

    There are some owl species that do migrate and some that don't. Northern and Flammulated Owls eat mainly insects, so they migrate to the southern United States and west central Mexico for the winter months. Saw Whet Owls rely on small mammals for food, so their distance of migration is much shorter (200 or 300 miles). The Great Horned Owl, another common resident here, eats from small mammals up to raccoons or skunks. They do not migrate at all and can eat year-round right here. (From Calen in Mrs. McCoy's class at Donnelly Elementary School in Donnelly)

  9. Why can't birds hibernate? Do they do anything like bears?

    They don't hibernate but there are some birds that will voluntarily lower their body temperature. For instance, Chickadees can do this at night where they can store up fat from the food they eat during the day. Then, they lower their body temperature at night so they don't have to keep their body as warm, using less energy. However they still have to shiver to keep some baseline level of warmth so their body organs won't fail. In the morning, they turn it back on, and in about half an hour their body warms back up again and is ready for flight. There is a bird that is related to the Night Hawk that will do this for longer periods. (From Leah in Mrs. Hunt's class at Cynthia Mann Elementary School in Boise)

  10. Why do birds travel as a group in a "V" formation?

    It has to do with saving energy. If birds can travel in a group like that and save energy while flying, they can travel further and more efficiently during their migration. So, the lead bird takes some of the brunt of the wind in the front and then they trade out over time. Those traveling in the back will eventually be up in the front, but while they are in the back, they can save energy by drafting off the lead birds. (More than 20 students from all over the state asked this question)