Many animals communicate using sound to attract mates, find food, and avoid predators.
Dave Wilson, a postdoctoral research fellow at the University of Windsor, says that rising levels of human-generated noise have raised concern for those animals. He is a member of a team of researchers who have published a new study this week in the Journal of Experimental Biology, which shows that traffic noise causes red-winged blackbirds to alter their songs.
“Understanding how noise affects songbird communication is important for assessing the effect of anthropogenic noise on species at risk,” says Dr. Wilson. “Some species adapt readily to noise, whereas others are less flexible and disappear from noisy areas. Red-winged blackbirds provide an excellent model with which to study the effects of traffic noise on birdsong; they are a common species, but results can be used to assess the potential effects of noise pollution on species at risk.”
The researchers compared the songs of birds living along a noisy Canadian highway to songs produced by birds living in pristine marshes that had never experienced traffic noise. They found that roadside birds produce songs with different characteristics than their counterparts in quiet marshes.
“Birds near roadsides produced songs with more tonality,” explains UWindsor biology professor Dan Mennill, co-author of the study. “Tonal sounds transmit farther amidst noise, and this change may be an adaptation to a noisy environment. For a male to reproduce successfully, his songs must be heard by nearby females, regardless of the acoustic environment.”
To understand better the effects of traffic noise on birdsong, the researchers played simulated traffic noise through a loudspeaker. They compared the songs birds sang during noise playback to songs before or after. Again, birds produced more tonal songs in the presence of noise.
“This shows that it was noise, not the presence of the highway or the traffic, that caused birds to change their tune,” Dr. Mennill says.
The playback experiment also showed that birds alter their songs rapidly in response to sudden noise, revealing surprising behavioural flexibility in this species.
Gabriel Blouin-Demers, a biology professor at the University of Ottawa and co-author of the study, says it is interesting that the birds do not permanently alter their songs.
“It suggests that the altered version of the song carries a hidden cost,” he says. “It might be more difficult for males to produce altered songs, or altered songs might be less attractive to females.”
The next step for the team is to investigate what those costs might be by measuring the survival and reproductive rates associated with traffic noise and the production of altered songs. Read the study in the Journal of Experimental Biology.