Grasshoppers Change Their Chirps In a Noisy World
It’s a noisy world we live in and even the grasshoppers are having to change their tune. A team of ecologists have found that these insects are changing their song to be heard over the sounds of road traffic, with possible consequences for their mating habits.
As Ulrike Lampe of the University of Bielefeld in Germany says in Science Daily,
“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.”
Indeed, to attract mating partners, male grasshoppers rely on “the undisturbed transmission of signals,” a challenge with increased levels of background noise that can “degrade or even mark” their sounds.
Certainly there are fewer and fewer places in the world where silence fully reigns, as cities and road systems expand and new airports and other transportation centers are built in what were once rural environments. The amount of “elevated background noise” has, without question, increased and all that noise can mask the sound signals that animals make.
Lampe and the ecologists collected 188 male bow-winged grasshoppers (Chorthippus biguttulus) from eight different places, half from roadside habitats and half from rural ones. The insects produce their mating song by rubbing a tooth file on their hind legs on a vein that protudes on their front wings. Here is what they found from analyzing some 1,000 songs:
Comparing courtship songs of males from roadside and control habitats, we found that roadside grasshoppers produced signals with higher frequency components in the low-frequency band of their signals (i.e. 6-9 kHz). Low-frequency road noise at major highways is easily loud enough to degrade or mask this part of the grasshopper signal spectrum. Fine-tuning song frequency upwards would allow grasshoppers to shift their signals to more “private” frequency ranges.
The ecologists are now seeking to find out how the grasshoppers are able to shift the frequency of their songs. Do they adapt to the noise during their development as larvae, or do males from noisy habitats have genetic differences that lead them to produce different songs?
Previous research has shown that frogs, whales and birds (such as sparrows who tweet louder in urban environments) change their sounds due to noise pollution. The study by Lampe, which is published in the British Ecological Society’s journal Functional Ecology, is the first to note the impact of human-caused noise on insects and suggests that they employ strategies similar to those of birds and other animals to address the changes in their environments.
In other words, we humans are altering ecosystems profoundly in the name of what we call “development.” Noise pollution has been shown to make it harder for plants to have sex. Pollution is by no means just about discarded plastic bottles and bags, but the way we are infesting every place on earth with sounds of a most unnatural kind.
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