A new study by two Quebec researchers has found that birds flee from the path of an oncoming vehicle based on the posted speed limit, and not the actual speed of the vehicle.
Birds are known to adapt, said Pierre Legagneux, a behavioural ecologist at the University of Quebec in Rimouski.
Urban birds adjust their song frequencies to account for noise pollution and they tolerate closer contact with humans compared to their rural cousins.
Driving back and forth from his home to his laboratory while studying in western France, Legagneux wondered what triggered birds to get out of the way.
"I was doing that just because I had to do something while driving, and I found something to do was record birds flying in front of my vehicle," he said.
"I had no expectations at all. Just doing that was better than doing nothing — at the beginning."
Legagneux and colleague Simon Ducatez, from McGill University, calculated the distance at which their feathered friends would take off with a vehicle bearing down.
"I expected to find that birds of course would react to my own vehicle... but I found it was not the case at all. We found that birds were reacting to the average speed of the road," he said.
The study captured 25 species in flight. They looked at reaction distances for all species, and for the three most prevalent and the results were similar.
In an article published today in the Royal Society journal Biology Letters, they said the birds appear to have habituated to the local speed limit as one of the features of the landscape, like the risk of predators.
They believe they're also responding to "artificial selection," after less cautious birds were eliminated.
"Perhaps risk-prone individuals may have been killed, and only the shy individuals (have survived)," Legagneux said.
The average distance birds allowed between themselves and the approaching vehicle before initiating flight was shorter in spring and summer than in fall and winter, which led them to believe that naive, juvenile birds present in those early seasons were no longer around come fall.
The discovery could help conservation efforts, Legagneaux said.
"If you have an especially vulnerable species in one area, and you want to protect them... then I would suggest to make sure the speed limit is not changing all the time, and not exceeded by any driver," he said.