Hey Mr. Green, 

Q: Now that you’ve told us how many birds are killed by wind turbines, windows, towers, power lines, and cats, can you tell us how many more are victims of collisions with motor vehicles? 

—Thomas in Whistler, British Columbia

 Motor vehicles whack more birds than all other hazards combined. But because birds are so small, it’s hard to get an accurate count. Hit a moose and you’re likely to stop and inform authorities in law enforcement, conservation, and insurance. Hit a bird and you might not even notice. But researchers from the Smithsonian Conservation Biology Institute and the U.S. Fish and Wildlife Service who reviewed the results of available studies concluded that anywhere from 89 million to 340 million are killed in collisions with vehicles in the United States, while 13 million are killed in Canada. 

One study hints that birds may be evolving to avoid collisions. The authors observed that cliff swallows killed by cars had longer wings than the swallows that survived. They speculate that this could be an example of survival of the fittest, because shorter wings enable these birds to turn more sharply, thereby avoiding a collision with fate. 

This won’t be terribly comforting to some species and their human friends, because different birds apparently have different levels of vulnerability. Barn owls, for example, seem to be highly susceptible to collisions. I was delighted to see that the European starling, an invasive species, was also susceptible. Unfortunately, the house sparrow, a serious menace to native birds, doesn’t seem to be at risk. 

Those who dismiss evolutionary theory might claim that birds can’t change in response to environmental conditions, while some who happily embrace evolution might use this knowledge as an excuse to do nothing about bird mortality—the same geniuses who don’t worry about global warming because, well, after all, Earth was hotter 65 million years ago.