Mine! Big Brown Bats Vocalise To Claim Prey.

Big Brown Bat. Eptesicus  fuscus. Credit: Angell Williams

Big Brown Bat. Eptesicus fuscus. Credit: Angell Williams

It makes sense that bats would employ a complex system of non-visual communication. For social creatures that are active under the cover of darkness, problems such as collision avoidance, prey location and identification of conspecifics need to be solved efficiently and swiftly. Bats have overcome these issues through echolocation and vocal cues; For bats, life is kinda like one big game of Marco Polo only way more complex. New research performed at the University of Maryland has revealed yet another layer of complexity to bat communication, namely the ability to vocally persuade a competitor to back off when both are pursuing the same prey.

The team responsible for the discovery were conducting research that involved flying pairs of big brown bats (Eptesicus fuscus) together in a flight-room containing a tethered food item. While listening to playback of bat-vocalisations recorded during the study, the team noticed something unusual “…We noticed calls that appeared to be different from typical echolocation calls. We then investigated the context and function of the call by looking at things like bats’ position relative to one another and prey captures success related to call emission” says Genevieve Wright, one of the scientists behind the research.

What the team discovered was astonishing. Male E. fuscus were emitting a special social call that was used exclusively when foraging. These frequency-modulated bouts (FMBs) were emitted when two bats were diverging on the same food item and they served to dissuade the trailing bat from attempting to capture the food item. The bats were essentially calling dibs on their prey.

Just try and take my mealworm. See what happens... Credit: USFWS Headquarters

Just try to take my mealworm. I dare you. See what happens… Credit: USFWS Headquarters

The team found that the vocalisations were individually distinct and resulted in increased foraging success for the caller “It was neat to find out that only males were making this call, and also that it was actually related to their prey capture success i.e., that the call seems to “work” for its intended function. Also, finding out the calls were individually distinct added another layer of depth to the calls’ meaning/function”.

The researchers postulate that FMBs were only observed in males because they were more likely to encounter non-familair individuals when foraging. Females tend to form non-random aggregations with roost-mates and often leave the roost to forage at the same time, whereas males frequently roost alone or in much smaller colonies of males. As females are more likely to be foraging near familiar individuals, competition (and thus the need for a competitive vocal signal) is rendered practically redundant.

Bat communication is a fascinating area of research that continues to yield really cool discoveries. Take for example the 2013 study which found that Spix’s disc-winged bats (Thyroptera tricolor) may be able to utilise the cone shape of unfurling Heliconia and Calathea leaves of as a sort of “ear-trumpet” when trying to locate roost-mates. The bats roost in small groups inside the curled up leaves, but as the leaves typically only remain curled for a day or so, the group must locate new roosts constantly. The research published in The Proceedings of the Royal Society, suggests that the shape of the leaf serves to amplify the search calls of bats trying to locate their roost-mates by as much as 10 decibels.

If you review the available literature it seems clear that we’re only just skimming the surface when it comes to our understanding of communication in nature. As time progresses we’re beginning to learn that communication between individuals, and even between species, can take on forms that we’ve failed to consider and a complexity that we’ve failed to fully appreciate. Perhaps this is why the study of animal communication is such a fascinating area. It is a largely unexplored frontier in biological science, and one that never fails to deliver new and exciting discoveries.

 

Many thanks to Genevieve Wright for her input.

Sources:

 

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