Sound Advice
Volume 12, Issue 3, Fall 2009

Can You Croak a Little Louder?

If you’re going to be in Melbourne, drive quietly...

A study was recently published by ecologists from Melbourne University and the Australian Research Centre for Urban Ecology, who were trying to discover the reason that the number of frogs had declined significantly in the city of Melbourne. They came up with a surprising reason: traffic noise in the city is drowning out the male frogs’ mating calls, ruining their chance for subsequent mating.

It seems rather unfair for the croaky little guys that they typically emit a low-frequency call to attract a mate, a frequency that is easily lost amid the low rumble of the traffic noise and other noise associated with modern society, such as air conditioners. However, some species, such as the southern brown tree frog, pictured above, have learned to compensate by raising the pitch of their call to be heard above the cacophony. The researchers' studies conclude that in doing so, instead of the male’s call being audible to females within the normal range of up to 21 yards, the higher pitched calls add another 16 feet to the range of audibility. It's the quintessential "Can you hear me now?" scenario.

This kind of adaptation has also been seen in other parts of the world where civilization has encroached on formerly natural landscapes. Ken Thompson of the University of Sheffield stated that his school’s research determined the reason British birds had begun singing in the night is that the traffic noise during the day was just too loud for them to make themselves heard. As Michael Crichton said in Jurassic Park, nature will find a way!

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