The Loh Down On Science

Here's an example of natural selection in action

And, now, a heartwarming story about roadkill!

This is Sandra Tsing Loh with the Loh Down on Science, saying, the numbers are going down!  

At least among cliff swallows in Nebraska.  So say husband-and-wife research-team Charles Brown and Mary Bomberger Brown.

For thirty years, they've studied the swallows who nest under bridges and overpasses.  This includes collecting swallows killed by cars.  Recently they noticed they were getting fewer dead birds than in the past.  

What had been twenty birds a season early on is down to five birds a season.

But the number of swallows has steadily increased, and traffic is about the same.  So what's going on?

The Browns got busy checking their data for answers.

Turns out, swallow wings are getting shorter!  Shorter wings mean faster turns.  And that means better avoidance of cars.

It's natural selection in action: birds with longer wings get killed more often, so they don't pass on their longer-wing genes to as many offspring.

Not that being hit by cars is natural, exactly.  But you know what we mean.

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The Loh Down on Science is produced by LDOS Media Lab, with 89.3 KPCC. And made possible by the generous support of the Gordon and Betty Moore Foundation.

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