In many parts of the world, Fall is punctuated by the calls of birds flying in formation overhead on their way south for the winter.
The commonplace sight may not arouse much interest in you most of the time. But if you pause to think about it, the fact that many of these birds are on a journey hundreds or thousands of miles long is remarkable.
Migrating birds fly incredible distances based on instinct alone—but why do they do it? The obvious answer might seem to be “to escape the cold,” but there’s much more to it than that.
Do All Birds Fly South for the Winter?
Winter in your area might seem devoid of birds. But not every bird embarks on a winter migration: this is a ritual only performed by certain species.
Birds that migrate are called migratory birds, while birds that don’t are called sedentary birds. About 40 percent of birds migrate for the winter regularly. However, to complicate things further, some bird species migrate partially: some individuals fly south, while others stay put.
Migrating also doesn’t always mean flying south. Some birds migrate between altitudes: they live in higher elevations during summer and fly to lower ones for the winter. Others might make a periodic mass migration, called an irruption, in search of food. Still, others migrate to molt, so they can live somewhere safer while waiting for their flight feathers to grow back.
However, seasonal migration is the most common type of bird migration. And it doesn’t have much to do with cold weather.
Why Birds Migrate
Birds are very good at surviving in harsh weather. But while they might be able to live through winter’s cold and storms, finding the food and other resources they need is another story. Birds mainly fly south for the winter because they need food and nesting locations.
In the winter, the resources birds need tend to disappear. Insect populations and other food sources diminish in areas with cold winters, and safe nesting locations also become harder to find. Birds then fly south to warmer regions where food and shelter are easier to come by.
Some birds don’t migrate very far. But for those that make long-distance migrations, the journey is both harrowing and impressive. Thousands of years of evolution feed into these migratory instincts and scientists are still working to understand exactly what triggers the migration. Genetics plays a role, but changes in temperature and sunlight also seem to help tell birds when and where to go.
Scientists also don’t yet fully know exactly how birds navigate on their annual migrations. Young birds are often capable of making their first migrations alone. And the next spring, they return to precisely the place where they were born.
A variety of senses that we don’t understand yet helps them do this. For example, birds can sense the Earth’s magnetic field, and might even be guided in part by smell.
However they do it, these long-distance migrations are an essential part of birds’ survival. Studies suggest that birds with longer migrations have a higher chance of surviving the winter than birds with shorter migrations.
If you live in the United States, chances are good you’ll see birds somewhere along the migratory path this Fall. To learn more about which paths they take, check out these amazing interactive maps. And to see your favorite birds up close this season, check out these national parks that provide havens to birds on the migratory journey.