Vampire Bats Prefer Foraging for Blood With Close Friends

It’s often more fun to go out to eat with friends—especially if you’re a female vampire bat on the hunt for blood.

Vampire bats are very social animals. A new study finds that social nature extends beyond the roost. Researchers have discovered that female vampire bats prefer to meet up with close roostmates when they head out on their nighttime foraging excursions.

The results were published in the journal PLOS Biology.

“Vampire bats groom each other more than any other bat species. They also regurgitate food to their offspring and to other adults that are in need of food, including unrelated adults,” co-author Gerald Carter, assistant professor in the Department of Evolution, Ecology and Organismal Biology at Ohio State University, tells Treehugger.

“This level of helping those in need is rare among nonhuman animals. It makes vampire bats an interesting case study for understanding why cooperation evolves.”

Vampire bats (Desmodus rotundus) also roost together in hollow trees and caves.

“We know from watching interactions inside their roosts that they have long-term cooperative relationships, but we know almost nothing about how those relationships function outside the roost,” Carter says.

This lack of information on how social relationships function outside the roost was mainly the result of a lack of tracking technology, says co-author Simon Ripperger, a postdoctoral researcher at Ohio State. Both Ripperger and Carter also work at the Smithsonian Tropical Research Institute in Panama.

“People radio-tracked bats but radio-tracking does not provide the spatial resolution to properly quantify social encounters among foraging bats. People were able to directly observe several bats feeding on cows but it was difficult to know if those bats are from the same roost or even have a social relationship,” Ripperger tells Treehugger.

“We developed those novel proximity sensors that allowed us to keep track of pairwise associations 24/7 and in combination with our observations from captivity, we could finally figure out whether the ones foraging together are also the ones that roost in close proximity or groom each other or share food.”

Feasting with Friends

For their study, Carter and Ripperger attached those new small sensors to 50 female common vampire bats—27 wild bats and 23 that had been captive for nearly two years. Then they released them back into the wild on a cattle pasture in Tole, Panama.

They found that bats rarely left the roost together, but closely bonded females often got together again far from their home base.

“After departing the roost individually, foraging bats more often meet up with the groupmates with which they cluster, groom, and share food,” Carter says. “These can be kin or nonkin.”

Recordings of vampire bat calls in La Chorrera, Panama, found that there are three distinct types of calls that they use: social calls that are downward and sweeping, antagonistic “buzz”-type calls, and “N-shaped” feeding calls. These feeding calls haven’t been observed by researchers in vampire bats.

The authors believe that the downward sweeping calls might help bats identify whether other bats are friends or enemies when they are flying. They hypothesize that bats might meet up with partners from the roots that they trust to make foraging trips for blood more successful.

“We suspect that close social partners would be more likely to share the animal or even the wound, whereas strangers might be more likely to fight over food,” Carter says.

“One advantage of co-foraging might be saving time during foraging,” Ripperger adds. “If a partner already opened a wound—a process that can take up to 40 minutes—a bat could drink straight from the open wound and be back at the roost quicker. That would lower the predation risk and create time resources for other activities (like mating).”

The findings are interesting, but they are also important in order to understand how vampire bats spread pathogens, the researchers say.

“One reason to do these studies is simply to understand the social lives of these animals. That's my main motivation,” Carter says.

“But another important reason is that vampire bats can spread pathogens like viruses to livestock and even to humans. By closely tracking how vampire bats hunt and interact with each other, we hope to make models of how pathogens might move through this system. That's what we are working on next.”