Heavy Traffic Breeds STOL Birds

Birds evolve shorter wings to survive on roads 

Charles Brown of the University of Tulsa in Oklahoma has been picking up dead swallows for 30 years. Roadkill numbers have steadily declined since the 1980s, even as the number of roadside nests has risen. The killed birds have longer wings than birds caught in mist nets for research, and on average the caught birds' wings have got shorter.

It makes sense: shorter wings are better for a quick vertical take-off, and improve manoeuvrability.

"Everything fits with the idea that it's vehicular selection," says Ronald Mumme of Allegheny College in Meadville, Pennsylvania.

However, Brown says that encounters with traffic may not be the only force at work. After a particularly cold May in 1996 killed about half the nesting population through starvation, wing lengths dropped markedly, perhaps because birds with shorter wings were better able to capture the remaining insects still on the wing.

People are so shocked to find that evolution is still going on around them.  Why?