Traffic noise reduces bats' ability to feed

By Patrick Barkham

The thunder of road traffic is likely to drive away bats, according to a study, which found vehicle noise caused bat activity to decrease by two-thirds.

While environmental assessments of new roads focus on the danger of habitat fragmentation, or bats colliding with traffic, the first ever controlled field experiment to investigate the impact of vehicle noise suggests noise pollution could be highly damaging.

Researchers played noise recorded from the A38 dual carriageway in Devon, with a “dusk average” of 26 vehicles passing per minute, in locations where different bat species flew and fed. The wild bats, including pipistrelle species, Daubenton’s and the greater horseshoe bat, were monitored with bat detectors placed beside, and 20 metres away, from the recorded noise.

Ultrasonic sounds from vehicles were found to impede some bat species’ high-frequency echo-location calls, which they use to find insect prey such as moths. But more significant was that most bat species sought to avoid audible traffic noise.

“Just like us, bats are likely to find audible road noise an irritation, something they would prefer to avoid rather than it jamming their echo-location,” said Fiona Matthews, professor of environmental biology at the University of Sussex and co-author of the paper in Environmental Pollution.

Matthews said the effect of ordinary traffic noise on bats meant that the adverse impact of new roads on bat populations was likely to be more far-reaching than realised.

She said: “This is important, as it means we could expect to see negative effects continue at a considerable distance from the road. We know that lower frequency road noise travels well beyond 50 metres – the scale at which ecological impact assessments are conducted.”

Dr Henry Schofield, from Vincent Wildlife Trust, which jointly funded the research, said: “We have become increasingly aware that bat species face barriers in the landscape that impede their ability to access suitable feeding areas and reduce their chances of survival. Along with habitat fragmentation and artificial lighting at night, this research has added road noise to the list of anthropogenic factors reducing habitat quality for these protected species.”

While studies have shown that traffic noise causes birds to sing more loudly and be less responsive to alarm calls, there has been little research on how it affects other wildlife.

The relatively silent streets during the coronavirus crisis appear to be a boon for many species, and the researchers are hoping to study the impact of much-reduced traffic levels on bats.

According to lead author, Domhnall Finch, the findings suggest formal ecological impact assessments should be required whenever there are significant increases in traffic flows, not only when new roads are built.