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Australia's frogs are having trouble finding love. Traffic noise and other sounds of city life, such as air conditioners and construction noise, are drowning out the mating calls of male frogs in urban areas, leading to a sharp drop in frog populations. But, in the first study of its kind, Parris, a scientist at the University of Melbourne has found that some frogs have figured out a way to compensate for human interference in their love lives.
A male southern brown tree frog sends out a mating call when he's looking for a date. It is music to the ears of a female southern brown tree frog. But, add the sounds of nearby traffic and the message just is not going out. Parris spent seven years studying frogs around Melbourne. She says some frogs have come up with an interesting strategy for making themselves heard.
"We found that it's changing the pitch of its call, so going higher up, up the frequency spectrum, being higher and squeakier, further away from the traffic noise and this increases the distance over which it can be for heard," Parris said.
The old call is lower in pitch. The new one is higher in pitch.
Now, that may sound like a pretty simple solution. But, changing their calls to cope with a noisy environment is actually quite extraordinary for frogs. And while the males have figured out how to make themselves heard above the noise, Parris says it may not be what the females are looking for.
"When females have a choice between two males calling, they tend to select the one that calls at a lower frequency because, in frogs, the frequency of a call is related to body size. So, the bigger frogs tend to call lower," she explained. "And so they also tend to be the older frogs, the guys perhaps with more experience, they know what they're doing and the women are attracted to those. "
Frog populations in Melbourne have dropped considerably since Parris began her research, but it is not just because of noise. Much of Australia has been locked in a 10-year drought, leaving frogs fewer and fewer ponds to go looking for that special someone.