This is Scientific American 60 Second Science.

I'm Christopher Intagiyata.

Every winter, huge hordes descend upon the parking lots of big box stores.

I'm not talking about Black Friday shoppers, but

crows. There's videos of them all over YouTube.

As you can see they're in the trees. They're on the rooftop over there and it's like hitchcocks the birds.

So sometimes there are 4,000 10,000 even 20,000 birds in these flocks.

Andrea Townsend is a behavioral ecologist at Hamilton College in New York.

They're really noticeable because what they like are urban areas.

So you'll see them in well-lit urban parking lots that's sort of their favorite place to spend the winter.

Crows, she says, are what's known as partial migrants. Every year, some members of the population migrate between breeding grounds and their overwintering grounds, like parking lots.

But others, just stay put. So Townsend and her colleagues wanted to know if that urge to migrate was something individual crows can turn on and off.

To find out, they captured 18 crows from overwintering spots in California and New York.

They fitted the birds with little backpack satellite tags and tracked

them for several years. Overall three quarters of the birds migrated an average of

300 miles and more importantly if they migrated once they did it every year, suggesting

traveling is not a habit they switch on and off. The researchers also found that

migrating crows returned faithfully to the same breeding grounds every year,

but they were more flexible on where to overwinter,

which could be a good thing.

Birds with these flexible strategies can change their behavior when the

environment changes. Whereas other birds and other migratory

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