Confusion arises in the city for songbirds.

Noise pollution from humans is guilty of many things — causing whales to lose their way, killing giant squid, leading baby fish away from good habitat, and generally stressing out animals. But while we know noise pollution in the oceans is causing whales to yell their songs, scientists have only just discovered that it is also causing birds to change their tune — and it seems to lead to a problem with fidelity and mate selection.

Researchers have discovered that noise from roads and highways has caused some birds, including the Great Tit to change their songs to a higher pitch so that they can be heard over the din. However, the change makes them less attractive to mates…

Wouter Halfwerk, a behavioral ecologist at Leiden University in the Netherlands, and his colleagues looked closely at the songbird species and found that males sing at their lowest just before females begin laying eggs, “indicating it was the low frequency songs that really made the difference for the females,” states PhysOrg.

After the eggs hatched, the researchers conducted paternity tests on the newborn great tits to see which males had won out in the end, but also to see which males were actually also being duped into raising the young of another male. The results showed that those males that had been forced to sing higher than they would have liked, wound up losing out to those that stuck with the lower frequency songs, which means other males had swooped in at the last moment with their low songs enticing the females out of the nest for one last tango just in time to fertilize her eggs.
While the females prefer the lower pitched songs, they can’t always hear them with background noise like that coming from roads and highways. The males with the higher frequency tunes could win out in those instances. The researchers found that noise pollution could be causing a serious swing in which males the females mate with, and therefore alter the strength of the species. The authors knew that several bird species were reported to change the frequency of their song to deal with human-made noise pollution, however the extent of the negative impacts was unclear.

The authors state, “These data are critical for our understanding of the impact of anthropogenic noise on wild-ranging birds, because they provide evidence for low-frequency songs being linked to reproductive success and to be affected by noise-dependent signal efficiency.”