A clever frog uses manmade storm drains as a microphone, blasting his mating calls over long distances, a new study finds.
Male mientien tree frogs (Kurixalus diootocus) have figured out that city storm drains amplify their mating calls, according to the paper, published in the latest issue of the Journal of Zoology. The louder and longer the calls are, the greater the chances are that the male will find an available mate.
“Structures, such as wall surfaces, may change the acoustic environment for signals transmitted by animals,” wrote study authors Wen-Hao Tan and colleagues, “creating novel environments that animals must either adapt to or abandon.”
Tan, a researcher in the Department of Life Science at National Taiwan University, and his team conducted field experiments and noticed that frogs intentionally went into city storm drains in Taiwan and then let loose with their mating calls. In fact, the males “selected perches inside drains that facilitated call transmission,” according to the researchers.
The frogs therefore found their own sound sweet spots in the drains that improved both call duration and amplification.
The scientists next created a replica of a concrete drain in a lab and introduced frogs. Once again, males went for the drain — and to spots with good acoustics — to do their calling.
This species is relatively small and has a higher pitched call than other frogs native to Taiwan, so it needs all the help it can get.
As for what female frogs think about all of this, the researchers report that “females have been observed coming to drains or perching on nearby vegetation.”
Open concrete drains are a common feature in suburban and rural areas across Taiwan and are usually built alongside paved roads or foot-trails. The researchers refer to them as “miniature urban canyons.”
Although male frogs gain acoustic advantages thanks to the drains, their use might not be so good in the long run. For example, animals monitor calls to help determine a potential mate — or a potential competitor’s fitness. Humans do this too, associating a person’s voice with their size and emotional and physical states.
If the vocalization isn’t a true representation of the individual, natural selection could be affected. Likewise, the drains are also clearly affecting wildlife habitat.
In the short term, though, tiny male frogs seem to be benefitting from their drainpipe crooning, with listening females swooning nearby.
Photo: A male mientien tree frog. Credit: Wen-Hao Tan et al., Journal of Zoology