The rising level
of noise in urban areas may be preventing some species of songbirds from
setting up home in developed areas, a study has concluded.
Canadian researchers found that noisy surroundings masked the lower
frequencies of bird songs, affecting the way some species communicated.
Unable to hear all elements of a song, females could perceive singing
males as ill-suited mates, they added.
The findings have been published in the
Global Change Biology journal.
"There has been a growing interest in preserving or increasing the
biodiversity of songbirds in urban areas," explained co-author Darren
"At the same time we know that these areas have pretty high levels
of anthropogenic noise.
Dr Proppe, now based at Calvin College, US, but carried out the study
while based at the University of Alberta, added: "We sometimes find areas
within cities that have what seems like suitable habitat, yet we get lower
diversity (of songbirds).
"So we wanted to investigate the hypothesis that there was link
between bird diversity and noise levels."
City bird limits
In order to do this, the team surveyed species at 113 sites in natural
areas within the city of Edmonton.
"What we found was that the number of species we had at each
location tended to be lower when noise levels were higher," Dr Proppe
"The decrease in species richness was one of the study's major
He said that the study also focused on seven species that did inhabit
the area to see if their abundance was affected as the urban noise increased.
The species that were selected met a number of criteria, including:
relatively common across the study area; forest or forest-edge dwelling; some
elements of the species' songs overlapped by the dominant frequencies of road
"What we found is that three of the species did have lower
abundances in locations that were noisier," Dr Proppe explained.
He added that the team did find that the presence of lower frequency
elements in a song was predictive of whether a
species' abundance would be affected by noise.
"This potentially could be down to the fact that those lower
frequencies could be overlapped by the dominant frequencies of road noise,
which also tend to be fairly low, resulting in a masking of communication
"We certainly know that birdsong and the perception of songs by
females for mate selection, so in the paper we did speculate that maybe this
was a mechanism these observed declines were occurring."
He suggested that females may perceive the song as abnormal if they
could not hear the lower frequencies and, over a period of time, this could
have a potential impact on the abundance of the species as if adults were not
pairing and mating then the number of offspring would decrease as a result.