How do birds know when to migrate?
ST. PAUL, Minn. — The sounds of spring are singing across trees and lakes. Some birds are returning to Minnesota as others are just passing through.
How do birds know when to migrate? And will our record-warm winter impact their schedule? Good Question.
The annual field trip for elementary school students to the Bell Museum happens every spring, right around the same time the very birds the kids are learning about make their yearly trip across the world. Some, however, never left, including cardinals and chickadees. About a third of bird species in the U.S. stay put through the winter.
"There's many strategies for dealing with cold winter temperatures," said Keith Barker, an ornithologist who is the curator of genetic resources at the Bell Museum.
Why do birds migrate?
"Birds migrate we think mostly because of limited resources," he said. Lakes freezing over and insects dying off make food hard to find, often pushing birds to fly south.
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"How do they know when leave? How do they know when to return? They're using a combination of internal clocks and local environmental conditions," Barker said.
As the days grow shorter in the fall, birds will eat like crazy in preparation for the long journey ahead.
Temperature change is another factor that reminds them when it's time to fly away. Given our recent warm winter, it could have led some birds to stick around longer since food wasn't as scarce.
"We know in general with climate change, birds are generally showing up on the breeding grounds earlier and they're starting to breed earlier. And we think some of that is based on temperature," said Barker.
Not all birds we see in Minnesota are coming home, some are just passing through. Tundra swans spend their summers on the northern edge of Canada, but winter along the east and west coasts of the U.S. Their migration route takes them through Minnesota, meaning they'll stop to rest and eat in the North Star state for just a couple of weeks both in the fall and spring.
What is the variance in the distance that some birds will travel?
"It's huge," said Barker. Snow geese will spend winters in the southern half of the U.S. and even parts of Mexico, whereas shorebirds will fly all the way to South America.
Is the migration route instinctual or learned? Barker said it is both.
"There are definitely instinctive aspects, things like being able to detect direction from the earth's magnetic field," he said.
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The part that is learned is similar to how humans find their way in the wild.
"Some species navigate by the stars, and they have to learn what cues to associate with north and south," he said.
When looking up at formations of birds in the sky, people might see dozens to hundreds to thousands of species all migrating at the same time. Others, like warblers and sparrows, fly alone when migrating.
