Drowned Out

The roar of cars and trucks along highways is making some grasshoppers change their mating songs, scientists report in Functional Ecology.

Researchers have already shown that animals will alter their tunes in noisy places. Birds in cities, for instance, sing higher-pitched songs than birds in the countryside. The study authors wondered if grasshopper songs would also change in response to noise. To produce songs that attract females, male acridid grasshoppers rub their hind legs and wings together.

The team collected 188 male grasshoppers from 16 places in Germany. Half the locations were near highways, and the other half were in quieter areas. Next, the researchers recorded 952 of the insects’ mating songs in the lab and analyzed the tunes’ properties, such as frequency, volume, and length of phrases.

In a lower-frequency range that overlaps with traffic noise, the roadside grasshoppers sang the loudest at a frequency of 7622 Hz, while the other grasshoppers’ volume peaked at a frequency of 7319 Hz. The study “suggests that grasshoppers use higher frequencies in the presence of elevated background noise levels to avoid signal degradation or masking,” the authors write.

The longer the highway had been present in the area, the more marked the shift was. So the altered songs are likely the result of genetic differences rather than short-term behavior changes, the authors say. Roberta Kwok | 13 November 2012

Source: Lampe, U. et al. 2012. Staying tuned: grasshoppers from noisy roadside habitats produce courtship signals with elevated frequency components. Functional Ecology doi: 10.1111/1365-2435.12000.

Image © Ulrike Lampe