Grasshoppers alter songs to be heard above man-made noises
Grasshoppers that live in noisy urban environments are having to change the tune in which they sing to each other in order to make themselves heard, ecologists have discovered.
Researchers suggest that high levels of background noise may affect the grasshoppers' mating process.
They say the insects are forced to increase the volume of the low-frequency sections of their call.
The study is the first to show that man-made noise affects natural insect populations.
Ulrike Lampe and colleagues from the University of Bielefeld in Germany caught 188 male bow-winged grasshoppers (Chorthippus biguttulus), half from quiet locations and half from beside busy roads.
Analysis of almost 1,000 recordings revealed grasshoppers living beside noisy roads produced different songs to those living in quieter locations.
According to Lampe: "Bow-winged grasshoppers produce songs that include low and high frequency components. 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."
The team's findings are important because traffic noise could be upsetting the grasshopper's mating system.
"Increased noise levels could affect grasshopper courtship in several ways. It could prevent females from hearing male courtship songs properly, prevent females from recognising males of their own species, or impair females' ability to estimate how attractive a male is from his song," Lampe explains.
Having discovered that man-made noise affects insect communication, the researchers now want to learn more about how the mechanism works, and whether the grasshoppers adapt to noise during their development as larvae, or whether males from noisy habitats produce different songs due to genetic differences.
The study has been published in the British Ecological Society's journal Functional Ecology.