Back when Darwin visited the Galapagos, he noticed that finches had evolved beaks in varying shapes and sizes to deal with eating different foods. Now birds probably long for the days when all they needed to worry about was keeping away from predators and finding their next meal. New research from Charles Brown at the University of Tulsa in Oklahoma has found that cliff swallows (Petrochelidon pyrrhonota) have evolved shorter wings to deal with motor traffic. With 80 million feathered friends being killed by cars each year, humans may be a literal driving force for their adaptation.
Cliff swallows have the habit of nesting underneath bridges and along roadsides, making them vulnerable for being hit by cars. Brown has been following their numbers since the 1980’s, and he noticed that their roadkill numbers have steadily declined for the past three decades. He measured the wingspan of dead birds struck by vehicles as well as live ones captured in mist nets for research. What he found was that the dead specimens had longer wings while the length of the live ones have become shorter. The advantage to having shorter wings means that the cliff swallows are better at a fast vertical takeoff as well as allowing for better maneuverability.
Although dodging Dodges on the road might seem to be the major contributor to this change in the birds’ bodies, Brown stresses that other factors could be at work. A cold may in 1996 killed half of the nesting population from starvation, causing a marked drop in wing length. Brown posits that those with shorter wings were better equipped to catch the last remaining insects. As for Darwin’s Galapagos finches, they also seem to be influenced by human behavior. Two formerly diverging populations look as though they are merging back into one as their natural diets are being replaced by food from bird feeders.
Via New Scientist