Singing Above the Din

grasshopper

Grasshoppers are increasing their singing volume to be heard over traffic noise. (Photo credit: Photodisc/Getty Images)

Road noise can be a nuisance for those who live near busy streets. But have you ever considered what effect road noise might have on other animals?

Research has shown that human noise can impact the vocalizations of a wide range of animals, including birds, mammals, and frogs. Up to this point, however, most research has focused on vertebrates. Recent research indicates that even the mating call of grasshoppers might be affected by noise associated with busy roadways.

The reproductive success of grasshoppers depends on being heard. To woo mates, male grasshoppers perform a courtship song by rubbing a toothed file on their hindlegs against a protruding vein on their front wings. If a female grasshopper likes what she hears, she responds, and the male approaches the calling female to mate. Typically, female grasshoppers prefer songs featuring low-frequency tones. Unfortunately, these low-frequency tones are the same tones that coincide with road or highway noise.

The possible effects of road noise on animal communication could be particularly significant, as the noise from cars and other vehicles is one of the most pervasive types of noise–just consider how many roads there are near where you live! If any noise might adversely affect how animals talk to one another, the cacophony of cars and trucks speeding down the road would seem the ideal candidate. This is exactly what scientists at the University of Bielfeld in Germany thought might be hampering the successful mating calls of grasshoppers, an insect found in droves along many roadsides.

Prior to conducting their experiment, the scientists hypothesized that male grasshoppers that inhabited noisy environments would produce songs that avoided being masked by traffic noise.

To test their hypothesis, they collected grasshoppers from both noisy and quiet habitats. In a lab setting, they stimulated each male grasshopper to perform a courtship song by exposing it to a female grasshopper from its same population.

Bow-winged grasshoppers produce songs that include low and high frequency components, Dr. Ulrike Lampe said in a news release about the research. We found that grasshoppers from noisy habitats boost the volume of the lower-frequency part of their song, which makes sense since road noise can mask signals in this part of the frequency spectrum.

Thus, the lower-frequency noise from highways or other human-made disturbances could seriously impact grasshopper courtship, according to Dr. Lampe.

It would prevent females from hearing male courtship songs properly, prevent females from recognizing males of their own species, or impair a female’s ability to estimate how attractive a male is from his song, he said.

Such impacts are a potential concern as they could lead to population declines in areas where the insects are not able to communicate with one another, and thus are unable to reproduce. For now, the researchers plan to continue studying grasshopper songs. They are particularly interested in learning more about the mechanism behind their song production and whether song differences between grasshoppers in noisy and quiet habitats are due to genetics or are somehow learned during development.

More to Explore
Grasshoppers Change Their Tune to Stay Tuned Over Traffic Noise
Staying Tuned: Grasshoppers From Noisy Roadside Habitats Produce Courtship Signals with Elevated Frequency Components
Traffic Makes Grasshoppers Sing Higher, Louder

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