Early sightings of leks and courtship behavior in wrinkled-faced bats

Wrinkled-faced bats not only have the most twisted faces of any bat species, the males also have a flap of white, hairy skin that they can pull over the lower face, not unlike the masks people wear. In a new report published in PLOS ONE, Smithsonian researchers and colleagues describe early observations of courtship in this species.

“This was an incredibly lucky encounter with these rarely seen ‘masked seducers’,” said Marco Tschapka, research associate at the University of Ulm’s Smithsonian Tropical Research Institute.

In September 2018, during a night walk in San Ramon, Costa Rica, two nature guides noticed several “ugly” bats hanging from some low branches near a path. They called friends who know bats, who in turn called their professor, Bernal Rodríguez-Herrera at the University of Costa Rica.

“Most people think all bats are ugly, so at first I didn’t take the report very seriously, but when they sent the photos, we realized these animals were bats with wrinkled faces, Centurio senex , an incredible discovery, “Rodríguez said. “Not only is this a rare bat species that many bat researchers wish they had on their life lists, these bats were doing something no one had ever seen before.”

Rodríguez called Tschapka, who was in charge of a golf course in Costa Rica. Tschapka jumped at the opportunity to join the project led by Rodriguez-Herrera and see not just one, but many wrinkled-faced bats together. .

“We never expected to see these bats in San Ramon,” Tschapka said. “Their range extends from Mexico to Colombia and Venezuela, but we hardly ever catch them in our nets. If I were desperate to find one, I would probably go to the dry, flat forest in northwest Costa Rica, but never in a rainforest. “

The bats perched close to each other in a relatively small area, hanging from trees and shrubs just 2.35 meters (about 8 feet) above the ground. They were all males, easily recognizable by the obvious facial mask which is present only in adult males, never in females. Each evening, the bats began occupying their perches at around 6pm. By midnight they were gone again.

The team soon suspected that this incredible discovery was actually a group of males performing in front of a female crowd. They recorded the behavior of the bats with an infrared-sensing handheld video camera and made audio recordings using an ultrasonic microphone connected to a computer. Perched males with their masks pulled up over their faces spent most of their time twisting their wing tips and making ultrasonic echolocation calls, occasionally interspersed with longer chirps.

But when another bat approached, a singing male became very agitated, began flapping its wings together, and finally ended its performance by thrusting its body forward towards the visitor while emitting a loud, audible whistle.

“I wish I could be there,” said Gloria Gessinger, a Smithsonian colleague who analyzed the sounds of bats at the University of Ulm in Germany. “In video recordings you can hear them whistling across the forest from different distances. It sounds so amazing!” Gessinger found that the echolocation calls in these bats are truly unique, consisting only of the fundamental frequency, but without the multiple harmonic nuances typical of other leaf-nosed bat species.

On October 10, the team first recorded the mating of two wrinkled-faced bats.

“A woman obviously couldn’t resist the seductive calls of one of the masked singers anymore,” Tschapka said. “She joined the perched male and quickly went about their private affairs, thus confirming our idea that the males were there to attract the females.”

Over a six-week period, the team observed a total of 53 perches. The largest number of bats present at any time was 30 in early October, then their numbers declined. By October 31, there were no more bats on the site.

This aggregation of bats exhibits all the characteristics of lek mating, a system in which many males gather to perform for females. Some of the most famous examples of lekking animals are birds such as manakins and grouse. This type of courtship behavior has only been seen in a few bat species.

Now the team has more questions than answers. Since the lek they found was the first reported, they chose not to catch bats at the site for fear of frightening the animals. So, they still can’t be sure if most of the visiting bats were female or if the males also visited their roosting rivals. It would be extremely revealing to record the behavior of fast-moving visiting bats with a high-speed camera.

Furthermore, the exact role of the curious face mask is not yet clear: perhaps the fold of the skin offers some kind of protection or is the origin of an irresistible scent that attracts females. To find out, it would be necessary to catch the males in courtship as they congregate in a lek.

This rare sighting was two years ago and the bats have not returned.

“Last year I had my suitcase ready and ready to go … but … nothing,” Tschapka said. “We think these bats are nomads, they move a lot and maybe we will never see this behavior again in our lives. But who knows? We are definitely on the alert!”