Nature

17
Oct

These Bats Roost in Leaves That Act Like Hearing Aids

In Central and South America, there lives a bat—Spix’s disk-winged bat, to be specific. It’s a tiny bat, and apart from the suction-cup-like discs on its thumbs and feet, there’s not much notable about it. Well, except for where it likes to roost: in the unfurling leaves of Heliconia and Calathea plants, which are common in the tropics.

The conical leaves give the bats a place to spend the night, but Gloriana Chaverri, a biologist at the University of Costa Rica in Golfito, suspected the leaves’ shapes offer more than just shelter. She thought they may act as a sort of assistive device, amplifying the calls of other Spix’s disk-winged bats, sort of like a rolled-up piece of paper held to your ear.

Bats in Heliconia leaf
Unfurling leaves may offer more than just shelter for certain tropical bats.

To test it, she took some of the leaves into the lab, placed a microphone inside, and played bat calls outside. Here’s Brian Owens, reporting for Nature News:

The inquiry calls from outside the roost were boosted by as much as 10 decibels as the sound waves were compressed while moving down the narrowing tube — the same thing that happens in an amplifying ear trumpet. Most response calls from inside the leaf were boosted by only 1–2 decibels, but the megaphone shape of the leaf made them highly directional.

While the leaves raised the volume of the calls, they also distorted them, leading to confusion among the group as to which calls were from friends and which were from strangers. Again, just like a rolled-up piece of paper held to your ear. (Go ahead, try it out.)

That the bats’ roosts are acoustically beneficial could be dumb luck, or not. Chaverri and her colleagues next project is to see whether the leaves chosen by the winged mammals are better at amplifying sound than others.