It turns out that humans aren’t the only ones who struggle with noisy cities. Urban noise is having disruptive consequences for songbirds — causing them to change their songs and reproduce less effectively, according to a growing body of research.
Birds communicate with each other acoustically, relying on song to transmit predator warnings and for selecting mates. But increased noise produced by human activities forces them to sing louder above the cacophony, and as a result, the quality of their song is decreased and is often shorter in length.
A recent study published in the Proceedings of the National Academy of Sciences analyzed three species of cavity-nesting birds — western bluebirds, mountain bluebirds and ash-throated flycatchers, all of which have taken up residence near industrial sites in New Mexico.
The study found that birds living in the noisiest areas have irregular levels of stress hormones, including increased amounts of the acute stress-induced corticosterone. Chicks also had reduced body size and feather growth in the noisier areas. A 2016 study also backs up the idea that city noise can have reproductive consequences — revealing that for songbirds in louder areas, fewer eggs hatch and the chicks don’t grow as well.
Yet, a third study analyzed the Eastern wood pewee during times of high traffic, as well as 36-hour periods of road closures. The birds tended to adjust their songs to compete with loud traffic noise, which could lessen their chances of being heard by potential mates or even rivals trying to invade their territory.
“Traffic noise is associated with a decline in reproductive success and species richness, contributing to the decreased biodiversity of ecological communities and reduced fitness of individuals near roads,” the authors stated.
On a brighter note, the study reveals that short-term road closures can have positive effects on the populations, helping to restore birds’ normal stress levels and allowing them to perform at optimal levels — an idea that could play a role in conservation efforts.