People wearing masks is a common sight in most of the world nowadays. However, a wild animal covering its face is a rarity. As far as I know only a couple of species of bats from Central and South America wear masks.
I have a face mask in my jacket pocket, handbag and backpack, just to make sure that I won’t forget it when I go shopping. But these bats don’t have to worry about that – they always have their mask with them. It is a skin fold under their chin that they can raise with their thumbs (the only free fingers on their wings) to cover the lower part of their face.
Why do they do that? That’s not exactly clear, as not much is known about them (yet). Maybe they want to protect their face during sleep, as some of the bats raise their mask when roosting. But it seems that for at least one bat species – the wrinkle-faced bat (Centurio senex) – the mask has a special role during mating. As the name says, this bat has deep hairless folds of skin on their faces. In males the wrinkles are more pronounced, and only they have masks. Any difference between the sexes (such as the big colourful “tail” of peacocks) already suggests an importance for mating, for example to attract females.
Wrinkle-faced bats seems to form leks – clusters of males gathered in one area trying to attract choosy females. In these bats males gather in the night, hang from neighbouring trees, put on their masks and “sing” (that is, produce a series of different ultrasound noises). When a female lands next to a male, he takes off his mask and begins copulation.
But what is the purpose of the face mask? For now, it’s just speculation. Maybe together with the wrinkles it helps to direct the “song” ultrasounds? Maybe it helps to control of scent signals produced in the skin around their chin? The mask is whitish, so maybe it serves as a visual signal for nearby females? Maybe the shade of the masks says something about the quality of the male (like the condition of peacock influences the appearance of its feathers)? Although bats are active during the night, this species have relatively large eyes and sight may be an important sense.
One thing seems clear, the mask is not there to hide the wrinkled face from the eyes of the potential partner. Or to reduce the spread of the diseases…
You can find video recording of wrinkle-faced bats at the suspected lek here.
Photo and the main source of information: Rodrıguez-Herrera et al. (2020).
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