Traffic noise may endanger wild birds by making it harder for them to hear alarm calls, a study suggests.
Scientists in the US tested how the sound of a busy road affected the way black-capped chickadees and tufted titmice reacted to titmouse calls warning of predators nearby.
While traffic noise from speakers set up near feeding platforms did not stop the birds looking for food, it appeared to mask the alarm calls.
Five times as many birds approached the speakers when they broadcast alarm calls on their own than when alarm calls were competing with the sound of cars and lorries.
"There has been lots of work on how anthropogenic noise affects vocal production, but much less on the response of animals to signals in the presence of noise," said Professor Megan Gall, from Vassar College, New York State.
"Additionally, a lot of this work focuses on song, but we were interested in how noise might affect responses to an anti-predator vocalisation.
"These vocalisations are evoked by the presence of a predator and so are closely linked in time with a particular stimulus."
The findings, published in the journal The Condor: Ornithological Applications, indicate that traffic noise may increase birds' vulnerability to predators, say the authors.
Rindy Anderson, an expert in bird communication from Florida Atlantic University, who was not involved in the study, said: "It's interesting that the birds' foraging behaviour was not affected under any of the playback conditions, which suggests that the behavioural effects were due to the call playbacks being masked by noise, rather than the noise being simply aversive."
