It's that time of year again ... the days are getting shorter and colder and the skies overhead are filled with what seems like an endless array of migrating birds heading to their southern homes. I've never really questioned why birds fly South ... it makes sense that as food gets scarcer and temperatures start to dip, many species of birds take flight for warmer skies and more plentiful food. But leave it to my kids to come up with a question I never thought to ask: how do birds know where "South" is?  

Blackpoll warblers spend summers in Maine and migrate 2,000 miles to their winter homes in Venezuela. How do these birds find their way over these long distances from year to year? The only way to know for sure would be to ask a bird, but since they aren't squawking, scientists have to guess. It turns out, birds probably pick up their cues from directions written in the sky — stars, light and magnetism. Here's how we think they do it:

Constellations: Scientists think birds use constellations as navigational markers on starry nights.  

The sun: During the day, birds can gauge their direction by the position of the sun in the sky.

Magnetic fields: Scientists think birds can feel the magnetic pull of the Earth and use it to determine their direction.

So there's the answer. Got a kid-stumper you need answered? Leave a comment or send me an e-mail, and I'll try to dig up an answer.

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