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How Do Birds Know to Return in the Spring?

Ever wonder how birds 'know' when to return north in the spring? Iowa Outdoors magazine explains it for you (it's a light thing). | Iowa DNRCommon sense tells us birds fly south in the winter to escape the harsh conditions of the north, and return “home” in the spring when the weather improves. While that theory doesn’t fly in the face of truth, it isn’t altogether factual, given most birds are well-equipped to handle extreme temperatures.

What does trigger birds to bug out from their wintering grounds is bugs—or food availability, to be more exact. Birds have an uncanny knack of knowing when it’s time to get out of town or face possible starvation.

That instinct, according to now-retired DNR Wildlife Diversity Coordinator Doug Harr, can be somewhat linked to photo period, or length of day. As day-length grows, birds realize it’s time to seek out alternate, more abundant and emerging food sources to the north.

Reproduction also plays into spring migration, as extended daylight hours and warmer temperatures means less stress and more food availability, meaning larger clutches and better hatchling survival. And since birds are creatures of habitat, they tend to return to procreate in the exact nesting spot they vacated in the fall.

Did you know?
The first recorded migrations were chronicled more than 3,000 years ago.

This article originally appeared in the March/April 2009 issue of Iowa Outdoors magazine.

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