Birds might be paying more attention to road speed limits than some humans. A new study finds that some European birds factor in average traffic speeds when determining when they need to take off to safely avoid oncoming cars.
In a new study, published in this week's issue of the journal Biology Letters, scientists tested whether European birds standing on the side of the road altered their escape distances in response to how fast an approaching car was moving or to road speed limits. (Related: "North American Birds Declining as Threats Mount.")
Study co-author Pierre Legagneux, a biologist at Canada's University of Quebec in Rimouski, said the idea for the experiment occurred 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 said.
Using only a stopwatch and a notebook, Legagneux measured the reaction times of birds that he spotted on the edge of the road while traveling in regions where the speed limit ranged from about 12 to 70 miles per hour (20 to 110 kilometers per hour).
"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," Legagneux explained. "So I had the time elapsed, and because I also recorded our vehicle speed, I also had the distance."
Legagneux and his colleague, Simon Ducatez of Canada's McGill University, found that the birds—mainly carrion crows, house sparrows, and blackbirds—took flight earlier after spotting their car in traffic areas where the speed limit was higher.
Curiously, the birds did not seem to pay attention to the car itself. "They reacted the same way no matter the speed of the car," Legagneux said.
The scientists speculate that some combination of two things might be happening. First, it may just be a case of natural selection in which individuals that failed to take off quickly enough are killed. As a result, only those birds with traits that help them successfully escape oncoming traffic go on to reproduce.
Another possibility, Legagneux said, is that the birds are actually learning to adapt to different traffic speeds. (Related: "What Can You Do to Help Stop the Songbird Slaughter?")
Daniel Blumstein, a biologist and bird behaviorist at the University of California, Los Angeles, said he could easily see how learning might be taking place. Imagine, he said, a scenario in which a bird is foraging next to the road and a truck drives by.
"If the truck is moving fast, the bird is going to get knocked around by the vortices coming off that truck," said Blumstein, who did not participate in the research.
"So the bird, if it survives, is going to learn very quickly that the truck produced a very adverse experience ... One or a few trials of getting knocked around may be sufficient for the bird to learn that cars are approaching faster on certain roads than other roads."
But why did the birds seem to ignore the speed of the scientists' car itself? It's possible, Legagneux said, that the birds might have just learned that it's simpler to react the same way for any given section of road.
"This way, they are not spending a lot of time being vigilant by looking at the speed of each car," he said.
Legagneux thinks the findings have implications for making roads safer for wildlife. (Related: "Ethical Flap Over Birdsong Apps.")
"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," he said.
Follow Ker Than on Twitter.