Vampire bats call on their friends to share blood meals | Science

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A researcher holds a banded vampire bat.
Simon ripperger

During the darkest hours of the night, between 3 and 4 a.m., the vampire bats that inhabit the agricultural regions of Panama leave their roosts for their blood meal. One by one, they emerge from the hollow trees in which they live and fly into the night in search of grazing cattle. The bats, which have a wingspan of about 30 cm, hover around until they spot their victim. After a vampire bat sees its target, it will land on its back, crawl up and down, and then choose a spot to bite. Flying mammals use heat sensors in their noses to locate cow’s blood vessels. They prepare the wound site, shaving the hair off with their rough textured tongues. Finally, they drive their razor-sharp teeth into the flesh of the cow, creating a deep wound, and as the blood flows, they lapped it with their tongues.

And while they’re feasting, they can yell at their bat friends – but not in sounds humans can hear – to join them for dinner, according to one. to study published today in PLOS Biology.

Scientists know that bats are social creatures, especially females. They groom each other inside their dormitories and often regurgitate their meals to feed others who have failed in their nightly hunts. Much like humans and other animals, they seem to have social preferences. In other words, bats have friends in the dorms – the ones they roost or groom themselves next to – and others they may not be so close to. But how far these friendships go is less clear.

Researchers at Ohio State University wanted to know if the bats were feeding with friends or on their own. Their study found that although bats almost always embarked on their solo nocturnal journeys, they often joined with others to share meals. Plus, female bats that were friends and spent a lot of time together in the dorm were more likely to share their meals, says Gerald Cater, a behavioral ecologist at Ohio State University. His team has recorded three separate calls to restaurants that suggest friends are communicating with each other about available food.

Compared to other animals, such as primates or birds which are easy to observe in the wild, bats are more difficult to observe. They tend to live inside trees, caves, and other isolated areas, which they only leave for a few hours and often at night when humans cannot see. However, it is important to understand the behavior of bats. Vampire bats in particular can pose a real threat to livestock as they can carry rabies. As scientists learn how bats interact with each other and with their hosts, they can better understand how rabies spreads.

The team studied two colonies of Desmodus rotundus—Common vampire bats living near cattle ranchers in rural Panama. In the first spot, named Tolé, the team focused on a fairly large colony of around 200 to 250 individuals. Using nets stretched over the bat’s flight path, researchers captured and tagged 50 females with tracking devices, then monitored their movements for several days.

Catching bats and equipping them with tracking devices was a complex feat. “They are slippery and very difficult to handle,” explains Carter. His team wore sturdy leather gloves that bats couldn’t bite.

Vampire bats call on their friends to share blood meals

The tag used to track vampire bats was about the size of a finger.

Simon ripperger

The trackers informed the researchers of the location of the bats inside the roost and helped determine which bats were friends. The devices also let researchers know which bats later ended up at feeding sites. Bats that had more friends in the dormitory also met more of their friends on foraging flights, the team found.

In the second location, called La Chorrera, the researchers observed the bats as they flew towards a cowherd, where the scientists recorded their food interactions. Studying bats at night in La Chorrera was both an exciting and bizarre endeavor that required befriending the cows. “At first the cows would move away from me, but after a while they got used to me, so I became a member of the herd,” says Simon Ripperger, study author and Ohio biologist. State University.

To observe and record bats, he carried an infrared camera and an ultrasonic microphone capable of capturing the sound of bats, which is outside the range of sound that humans can hear. The microphone was connected to a computer inside his backpack and automatically recorded the sound waves emitted by bats. He couldn’t use any light as it would scare off bats, so he observed the animals through the infrared camera.

“I could see them moving over the cows and pinpointing where they could bite,” Ripperger recalls. “Then they would bite and I could see the blood running down the cows’ necks. I was so close it literally gave me goosebumps. . “

Watching the social interactions of the bats was fascinating, Ripperger says. As the mammals foraged, they clearly made various calls, either to attract other bats or to drive them away. Ripperger noticed that the microphone signal changed as the behavior changed. “I could see the bat’s mouth opening and closing,” he said, then more bats appeared. Sometimes they lapped the blood together and sometimes they fought over the wound. “I could tell there was a lot of communication during the feeding.”

While the cows were not in the study, Ripperger also learned something about them. Some cows did not react much to the bites. Some have tried to slap bats with their ears. One started to run and shook the creatures. And on two occasions when two bats crawled on the back of a cow, another cow came and knocked them out.

But the study focused on bats, and particularly female bats, as they are more social than males and keep friends within the colony. Males are much more territorial, according to the researchers. Inside the roost, they tend to be left alone and defend their positions against other males from the same colony, sometimes fighting with each other. Males do not develop friends, except when they mate with females.

Vampire bats call on their friends to share blood meals

A vampire bat with a tag flies away at night.

Sherri and Brock Fenton

Ultrasound recordings collected at the second study site revealed three distinct types of calls that vampire bats used to communicate. One was the social call which the researchers described as a ‘sweep down’ that they believed could be used to recognize or alert friends, while the second was an antagonistic ‘buzz’ that the team interpreted as “stay away”. A third call fluctuated from low to high and back to low – shaped like the letter “n” – which has never been recorded before. “We think it’s a call that they’re using to coordinate or compete for food,” Carter says.

These dietary communications may give notified bats certain advantages. For example, preparing a wound takes time and work, which makes bats more vulnerable to predators like owls. The longer they sit on the backs of cows for food, the more likely they are to become food themselves, Ripperger says. Bats aware of a prepared meal are able to fly quickly and feed, making them less likely to be eaten.

Brian Bird of the University of California at Davis, who also studies bats but was not involved in this research, says the study advances scientists’ understanding of bats. “It shows a greater complexity in how bats live their lives and how they have their social structure, and what you call friends,” he says.

More interestingly, it reveals that vampire bats – who often get a bad rap for their bloodlust – are no different from us. “It shows that the way bats behave in some ways is so similar to the way we humans behave,” Bird says. “They preferentially take care of family members and friends. “


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