We’ve long viewed vampires as lonely creatures of the night — solitary until they feast on human blood. But how true is that myth when it comes to vampire bats?
Vampires may not be real — sorry to any Twilight fans looking for their Edward Cullen — but vampire bats certainly are. Much like their mythical counterparts, vampire bats are the only mammals that subsist entirely on blood (though they’re far more likely to prey on cattle than humans).
However, these blood-sucking creatures aren’t as solitary as the legends suggest — and they may have much more in common with humans than previously thought.
These findings suggest friendship may be essential to the bloodthirsty bat’s way of life and help us understand the evolutionary behavior of one of nature’s most elusive nocturnal animals.
“We think this study opens up an exciting new window into the social lives of these mysterious animals,” co-author Gerald Carter tells Inverse. He’s the founder of the Carter Lab at Ohio State University.
Can animals be friends?
Social relationships are crucial to animal survival — just as they are for humans.
Animals tend to cooperate with members of their own species for survival. For example, recent research found bonobos engage in a strikingly sophisticated form of social cooperation known as joint commitment. This suggests they understand that their survival is dependent on the group’s success.
Vampire bats share by “regurgitating their ingested blood.”
Social cooperation becomes even more crucial in the context of feeding. Vervet monkeys, for their part, will strategically groom monkeys higher up in the social hierarchy to gain access to food.
“Social relationships can determine access to food,” write the researchers behind the bonobo study.
This close relationship between food and friendship also plays out among vampire bats, though in a slightly more gruesome manner. Vampire bats “reciprocally share food with each other by regurgitating their ingested blood” to bats in their roost, Carter explains.
However, until Carter and colleagues published their recent study, they didn’t know whether vampires that share food in their bat roosts would also hunt together outside the home.
They set out to capture footage of the vampire bat and, in the process, learn more about the complex nature of female friendships among bats.
How the discovery was made — While earlier GPS-focused technology wasn’t sophisticated enough to capture the necessary information about vampire bats’ foraging habits, recent developments in motion sensor technology have allowed for more accurate observations.
The study team used this technology alongside audio and video recordings of bats, as well as statistical models, to hone their findings.
What they discovered — Female bats who roost together also feed on the open wounds of cattle together — suggesting a new element of bat friendship.
The female bats may not necessarily leave their home roost at the same time, but they still end up foraging together. The human equivalent might go something like this: You invite your roommate to get drinks, you show up at the bar at 5:30 p.m., and they stroll in at 6 pm.
“Using recently developed proximity-sensor technology, what we found is that the bats depart individually but then reunite later while foraging,” Carter says. “They meet up more often with their preferred roosting associates.”
And while vampire bats may periodically change up their roosting partners at home, they still maintain preferred relationships with certain female bats. These are the bats they interact with while foraging: During these moments, the female bats spent noticeably more time interacting with close female acquaintances compared to strangers.
“Vampire bats are some of the most maligned of all bats.”
The study team initially wondered whether female bats might hunt separately to increase their chance of success, but it turns out that’s not the case— at least when it comes to sharing food with close friends.
Carter and colleagues speculate female bats were less likely to see these friends as competitors, whereas they would more aggressively compete with non-familiar bats over access to their food supply.
“... competition over food might be relatively low among familiar vampire bats that tolerate each other (as observed in captivity) and even share food, compared to unfamiliar conspecifics that might ‘steal’ a wound.”
They also found the more sociable bats — those who had more friends in the roost — also encountered more friends while feeding.
Finally, the researchers discovered a never-before-heard bat call associated specifically with foraging or feeding behavior.
Why it matters — Beyond informing a new understanding of female vampire bats, the study reveals overall insight into the evolution of one of Earth’s most misunderstood animals.
“Vampire bats are some of the most maligned of all bats,” Carter says. “People do have a reason to fear them because they can transmit rabies to livestock and people, but I do think they are beautiful and interesting animals in their own right.”
Far from being loners, the research reveals that bats have a rich social network of friends. This network just looks different than what we typically expect.
Rather than living in a stable group of animals — think a pack of lions — “each bat maintains its own network of close cooperative social bonds,” Carter says.
“Females seem to build up new cooperative relationships with strangers through clustering and mutual grooming, which eventually leads to reciprocal food sharing,” he explains.
What’s next — While vampire bats are surviving, other species of bats face the threat of extinction. Understanding how bats cooperate with each other during feeding could help with overall conservation efforts.
Since bats are vectors for disease, Carter also hopes these findings can eventually help track the transmission of infectious diseases from bat to cattle.
“In the future, we might be able to track every individual contact among the bats and their cattle prey,” he says. “We hope to gain insights that would be useful for disease ecologists.”
Ultimately, Carter says we are still “scratching the surface” when it comes to really knowing the vampire bat.
Abstract: Stable social bonds in group-living animals can provide greater access to food. A striking example is that female vampire bats often regurgitate blood to socially bonded kin and nonkin that failed in their nightly hunt. Food-sharing relationships form via preferred associations and social grooming within roosts. However, it remains unclear whether these cooperative relationships extend beyond the roost. To evaluate if long-term cooperative relationships in vampire bats play a role in foraging, we tested if foraging encounters measured by proximity sensors could be explained by wild roosting proximity, kinship, or rates of co-feeding, social grooming, and food sharing during 21 months in captivity. We assessed evidence for hypothetical scenarios of social foraging, ranging from individual to collective hunting. We found that closely bonded female vampire bats departed their roost separately, but often reunited far outside the roost. Repeating foraging encounters were predicted by within-roost association and histories of cooperation in captivity, even when accounting for kinship. Foraging bats demonstrated both affiliative and competitive interactions with different social calls linked to each interaction type. We suggest that social foraging could have implications for social evolution if “local” within-roost cooperation and “global” outside-roost competition enhances fitness interdependence between frequent roostmates.