Sunday, September 4, 2011

waiting zone
















These barn swallows (and many, many more), a mix of parents and young-of-the-year hatched here, wait for the trigger that tells them to start moving south.

What is that trigger? There are theories, but no hard facts. They leave this neighborhood long before their food base (flying insects) becomes scarce, probably moving gradually south until at some point they undertake the long flight to Central and South America, encouraged by cooler temperatures and shortening days.

Related posts are here, here, here, and here for anyone wanting to explore my obsession with barn swallows!
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