When copulating, male wrinkle-faced bats pull down a mask-like flap of facial skin, according to new research -- the first-ever behavioral survey of wrinkle-faced bats in their natural habitat.

Until now, scientists didn't know much about the mating patterns of wrinkle-faced bats, Centurio senex, a species that lives among the caves of Mexico, Central America and northern South America.

"Bats are small, nocturnal and they fly!" Bernal Rodríguez-Herrera, researcher at the University of Costa Rica, told UPI in an email. "It's not so easy to study the mating systems of bats."

For the study, published Wednesday in the journal PLOS One, researchers used ultrasonic sensors and infrared cameras to record the bats' vocalizations and mating behavior.

Wrinkle-faced bats use what's called lek courtship, during which females select mates from clusters of sexually displaying males.

According to Rodríguez-Herrera, the male bats don't defend any resources, like food or shelter, they only provide genetic material.

"The most common mating system to find in bats are those where the male defends and kept a resource," Rodríguez-Herrera said. "And for this reason, the females select it, a kind of 'harem.'"

Based on previous observations, researchers suspected wrinkle-faced bats used a lek system.

"In the Lek, it is common to be a sexual dimorphism," Rodríguez-Herrera said. "In Centurio, the skin mask is only developed by males. That sexual dimorphism made us think that it plays a role in the mating system."

The video evidence proved their suspicions correct.

Footage of the courtship process showed males emit loud, low-frequency whistling calls when females come to mate. When selected by a female, males pull down their mask-like skin flaps prior to mating, only pulling the flaps back up after copulation.

According to Rodríguez-Herrera, there are other closely related species that exhibit similar types of dimorphism -- species ripe for followup investigations. But first, Rodríguez-Herrera and his colleagues hope solve a few more of the wrinkle-faced bat's mysteries.

"I think an important one is to understand is what the criteria is that females use for choosing the male mate," he said. "Is it the vocalizations? Or the place of the male hanger? Odor? We don't know."

Researchers also want to figure out the cost-benefits of this particular courtship system.

"There are many questions. That is the beauty with this species, when you found it, many questions arise."

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