In a study published in a recent issue of the journal Biology Letters, scientists tested whether birds standing on the side of the road altered their escape distances in response to how quickly approaching cars were moving or in relation to road speed limits.
Researchers found that the higher the speed limit is on the road, the faster birds–mainly carrion crows, house sparrows, and blackbirds– would take off to avoid being roadkill. Interestingly enough, the birds didn’t react based on the exact speed of a particular vehicle. Instead, they seemed to observe posted limits in their own way–responding to the average speed of the road.
A biologist at Canada’s University of Quebec in Rimouskitudy and co-author, Pierre Legagneux, said the initial idea for the experiment came to him while he was commuting to his lab in France.
“I found [the commute] very boring so I had to do something while driving, so I started to record birds flying away,” Legagneux told National Geographic. “When the birds flew away, I started my timer and I fixed the point where the birds [were standing]. And when I passed over this point, I stopped my timer,” he explained. “So I had the time elapsed, and because I also recorded our vehicle speed, I also had the distance.”
Legagneux examined how some birds would take their time on slower roads and rush on ones that moved at a quicker pace.
“In other words, the birds appear to have adapted street savvy to survive alongside these strange metal-clad beasts, our cars, by judging their typical behavior,” writes Stephen Messenger at Treehugger.
This, of course, makes drivers who violate the speed limit especially hazardous to their well-being. According to New Scientist, more birds tend to get hit in the spring, possibly because young ones haven’t yet learned the rules of the road.
“If you have different speed limits for similar roads in similar landscapes, it could be dangerous for birds because they hardly have any cues of those changes,” cautions Legagneux, who believes the findings have implications for making roads safer for wildlife.
Over the last 30 years, cliff swallows that nest in highway overpasses even appeared to have evolved shorter wingspans to help them survive close encounters with highway traffic. Charles Brown, a University of Tulsa researcher who’s spent the last three decades picking dead birds off roadways, notes the mortality rate went down as more birds were born with shorter wings to enable mobility and faster take-offs.