While homeowners may appreciate a decked-out media room and surround sound in their abodes, one animal may be using a natural amplifier to help it communicate from its roosting home. A new study by researchers at North Dakota State University, Fargo, ND USA and the Universidad de Costa Rica shows that the furled leaves of Heliconia and Calathea plants where Spix's disc-winged bats make their home actually help to amplify and transmit the social calls of the bats. The findings of Dr. Erin Gillam of NDSU and Dr. Gloriana Chaverri appear in the latest issue of the journal Proceedings of the Royal Society B.
The disc-winged bats (Thyroptera Tricolor) use the lush leaves as their temporary homes to roost. The leaves naturally curl into a horn-like shape, making a safe place for the bats to live. When bats are separated from their social group, they call to each other, producing what are known as inquiry and response calls. The leaves act like a megaphone, amplifying the incoming and outgoing calls, which likely helps the animals keep better track of group members.
"Our study provides the first evidence of the potential role that a roost can play in facilitating acoustic communication in bats," said Gillam. "Essentially, we are trying to understand if bats potentially take advantage of the places they live to maximize the likelihood that their calls get to the desired receiver. Our study suggests that the structure of the leaf roosts used by these bats may help with this process."
Cliquish bats use leaves as hearing aids
The disc-winged bats move to a new house daily to avoid predators, as the leaves of their plant homes unfurl. The bats communicate to keep track of each other and keep their constantly mobile neighborhoods intact. Researchers found that when the bats call to each other, the curled leaves act as horns or megaphones to increase the sound by one to two decibels. For bats looking for members of their groups that had already found a new leaf home, the leaves amplified their calls by up to 10 decibels.
Native to Central America, the tiny bats weigh about four grams each. While the leaves appear to help the disc-winged bats communicate, the leaves don't necessarily provide high-fidelity sound. Study results show that the megaphone-like leaves can also distort the sound, but the effect on the bats is unclear, according to Chaverri and Gillam.
What'd you say?
In a previous study, it had been shown that bats within the leaf cannot identify bats flying outside of the group based on their inquiry calls; the distortion of these calls by the shape of the leaf could potentially explain why bats have trouble in making this distinction. But when it came to the bats' unique response calls, the flying bats could determine enough information to identify whether it came from a member of their group.
"This type of research helps us better understand the evolution of communication systems, which play key roles in many behaviors," explained Gillam. "For example, finding a mate generally involves males attracting females through a combination of visual, acoustic, and/or olfactory signals. This type of research helps us understand how natural selection has shaped these systems to their ecological and behavioral environments over evolutionary time."
Gillam and Chaverri are planning additional research. They plan to investigate whether the bats choose a prime piece of real estate leaf to roost because it provides maximum sound, or if they adapt their sounds to the shape of the leaf they've selected -- maybe akin to the way humans choose the perfect place to live, versus a fixer upper they learn to live with.
- G. Chaverri, E. H. Gillam. Sound amplification by means of a horn-like roosting structure in Spix's disc-winged bat. Proceedings of the Royal Society B: Biological Sciences, 2013; 280 (1772): 20132362 DOI: 10.1098/rspb.2013.2362
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