First observations of lek behavior and courtship in wrinkled-faced bats

Wrinkled-faced bats not only have the most convoluted faces of any bat species, but males also have a hairy, white patch of skin that they can pull across the bottom of their face, a bit like the masks that people wear. In a new report published in PLOS ONE, Researchers and colleagues at the Smithsonian describe the first sightings of courtship display in this species.

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

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

“Most people think all bats are ugly, so I didn’t take the report very seriously at first, but when they uploaded photos, we realized these animals were bats in the dark. wrinkled face, Centurio senex, an incredible discovery, ”said Rodríguez. “Not only is this a rare bat species that a lot of bat researchers would love to have on their life list, these bats were doing something that no one had ever seen before.”

Rodríguez called Tschapka, who was running a field course in Costa Rica. Tschapka jumped at the chance to join the Rodriguez-Herrera-led project and see not just one, but many bats ride together.

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

The bats perched close together in a relatively small area, hanging from trees and shrubs just 2.35 meters (about 8 feet) from the ground. They were all male, easily recognized by the obvious face mask that is only present in adult men, never in women. Each evening, the bats began to occupy their perches around 6 p.m. By midnight, they were gone again.

Soon the team suspected that this incredible discovery was in fact a group of men showing off in front of a crowd of women. They recorded the behavior of the bats with a portable infrared-sensing video camera and made sound recordings using an ultrasonic microphone connected to a computer. The males perched with their masks up on their faces spent most of their time twisting their wing tips and making ultrasonic echolocation calls, occasionally interspersed with sequences of longer trill songs.

But when another bat approached, a singing male would become very restless, start flapping its wings together, and eventually finish its display by pushing its body towards the visitor while making a loud, audible hiss.

“I wish I was there,” said Gloria Gessinger, a member of the Smithsonian who analyzed the sounds of bats at the University of Ulm in Germany. “In the video recordings, you can hear them whistling all around the forest at different distances. It sounds so amazing!” Gessinger discovered that the echolocation calls in these bats are very unique, consisting only of the fundamental frequency, but without the multiple harmonic harmonics typical of other species of leaf nosed bats.

On October 10, the team recorded the mating of two bats with wrinkled faces for the first time.

“A woman obviously could no longer resist the seductive calls from one of the masked singers,” Tschapka said. “She joined the perched male and quickly they turned to their private business, confirming our idea that males were there to attract females.”

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

This aggregation of bats shows all the characteristics of lek mating, a system in which many males congregate to introduce themselves to 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 observed in a few bat species.

Now the team has more questions than answers. Because the lek they found was the first reported, they chose not to capture the bats at the site for fear of scaring the animals. So, they still cannot be sure if most of the visiting bats were females or if the males also visited their perched rivals. It would be extremely revealing to record the behavior of bats moving quickly with a high speed camera.

Additionally, the exact role of the curious face mask is still unclear – perhaps the skin fold offers some sort of protection or is the source of an irresistible scent that appeals to women. To find out, it would be necessary to capture the courting males as they congregate in a lek.

This rare sighting dates back two years and the bats have not returned.

“Last year I had my suitcase packed and ready to go … but … nothing,” Tschapka said. “We think these bats are nomadic, they move around a lot, and we might never see that behavior again in our lifetime. But who knows? We’re definitely on the prowl!”