MIGRATION SECRETS
Discover how birds navigate their awe-inspiring travels.
IT’S ONE OF THE MOST ASTOUNDING PHENOMENA ON EARTH.
Every year in spring and fall, billions of birds worldwide are on the move to their seasonal homes. Everyone’s heard a fact or two about migration, but specific details about these major movements aren’t as well known. Here’s a primer on how these feathered travelers make their journeys.
Where do they go, and when? Not all birds are great travelers; some stay home. A downy woodpecker or a chickadee might spend its whole life close to where it hatched. Others do move, but only short distances. For example, certain kinds of grouse migrate by walking, putting only 10 or 12 miles between their summer and winter territories.
Birds of a feather don’t always flock together when it comes to migration. Some American robins fly from Canada to Florida in fall, but others in mild climates stay in the same place all year. An individual robin might even go south one year but remain up north the next.
On the other hand, some species make astonishing journeys every year. American golden-plovers travel from the tundras of northern Canada and Alaska to southern South America in fall. Arctic terns fly even farther, moving from the cold, northernmost Canadian islands or the north side of Greenland all the way to the edge of the Antarctic. They log some serious mileage—their yearly round trip can total more than 25,000 miles.
Although we typically think of birds as flying north in spring and south in fall, they don’t all fit that assumption. Some hummingbirds in the Southwest and Mexico begin their “spring” flight in January, and certain species travel east and west rather than north and south. A few sandpipers begin their “fall” migration before the end of June, and they start by flying east across Canada. Migration occurs every day of the year, and in every direction.
How do they find their way?
As amazing as it seems, an oriole that nests in your area could make its way to Central America, the Caribbean or even South America in fall. And in spring, the same oriole might return to your yard. Though it seems far-fetched, it’s not unique—most migrants match this feat.
A few birds, like geese and cranes, travel by memory. They fly in daylight and follow landmarks. Youngsters travel with their parents or with a flock of adults, learning and memorizing the routes. But the recollection-reliant are the exceptions. Most species have an instinct for where to migrate and can navigate on their own.
This is the case with most familiar migratory songbirds, like warblers, tanagers and buntings. Young birds often fly south after their parents depart, and instinct guides them to their wintering grounds. Since many fly at night, they use the stars as their guide. When they journey by day, songbirds navigate using the sun. Birds detect the Earth’s magnetic field, which helps them orient their travels, but scientists are still figuring out all the methods birds use to find a particular place with such accuracy.
What’s it like to be a migrating bird?
Birds don’t simply wake up in the morning and decide to migrate. For them, travel is just one part of a longer process. Before heading south in fall, a bird may molt, or replace, its feathers over several weeks, so it travels in fresh plumage. It’s likely to gorge itself on bugs or berries to build up stores of fat that serve as fuel on long flights.
Once the bird is ready to go, it waits for good weather. The typical small songbird migrates at night, waiting for an evening with clear skies and light winds blowing in the direction it wants to go. Just after dark, it takes off, climbing rapidly into the sky. As it flies through the night, often more than a thousand feet above the ground, it may give occasional callnotes. Around it in the dark, the bird hears the songs of other migrants—warblers, thrushes, sparrows and more—all traveling in the same direction.
When dawn arrives, the migrant comes down, seeking a place to spend the day. It may have to fly for miles to find a patch of suitable habitat. Then it rests and eats, building up strength for its next flight. It stays a day, a few days or more than a week before it eventually resumes traveling.
Depending on how far the bird is going, it takes anywhere from several days to a couple of months to complete its journey from breeding territory to wintering grounds. Once it settles in for the winter, it may join flocks of other birds or it may defend its territory, depending on the species.
Winter is a relatively relaxed time, absent the pressures of finding a mate and raising young. Then winter starts to shift to early spring and before long our little feathered travelers come north to visit us again.