Vampire bats form deep social bonds by grooming before sharing blood

March 19, 2020

For vampire bats, sharing blood with a roostmate is the mark of a true bond. Though these relationships are uncommon, they demonstrate behavior akin to what some might call friendship. In a paper appearing March 19 in the journal Current Biology, researchers show how social grooming and food sharing can build up trust among unrelated vampire bats to form life-saving bonds that can last a lifetime.

"We go from bats starting as strangers from different colonies to groupmates that act to save each other's life," says Gerald Carter (@gerrygcarter), a behavioral ecologist and assistant professor at Ohio State University. "This is the first animal study to look carefully at how a new cooperative relationship forms and can be maintained between complete strangers of the same species."

Vampire bats sustain themselves on only blood, and if a bat is unable to feed for 3 days, it runs the risk of starving. "They have this 'boom and bust' foraging experience, so they either hit it big and get a large blood meal or they're starved for that night. If they starve three nights in a row there is a high chance they'll die," says Carter. Because of this, vampire bats with close social ties can rescue their weakened partners from the brink.

To test how these bonds emerge, Carter and his colleagues collected bats from Las Pavas and Tolé, Panamá, two geographically distant sites. Bats were then placed either in pairs--one from each location--or in small mixed cohorts. For each group, the research team withheld food from one of the bats and observed how it interacted with its cagemates. Several bats, particularly those in the pairs, began grooming one another more over time, and in some cases, this eventually led to sharing blood with underfed companions.

"Even if you remove all ectoparasites from their fur, they still groom each other more than necessary for just hygiene," says Carter. "We think of social grooming as a kind of a currency--a way to gain tolerance and bond with another individual."

Furthermore, Carter suggests the increased grooming over time demonstrates "raising the stakes" of friendship. The idea of "testing the waters" or "raising the stakes" to build cooperative relationships was first proposed in a theory paper in Nature in 1998, but it has been difficult to demonstrate in animals. "When you make a cooperative investment in another individual, there is a kind of risk, because if you have a bad partner, you can be even worse off than if you had just avoided them altogether," he says. "So, what you could do is invest a little bit to test the waters. Then, if they invest back in you, that's a signal to ramp up your investment, and so on."

If pairs raise the stakes enough, one might provide food by regurgitating blood into the mouth of a hungry partner. Visually resembling a sort of French kiss, "food sharing in vampire bats is like how a lot of birds regurgitate food for their offspring. But what's special with vampire bats is they do this for other adults, eventually even with some previous strangers," says Carter. These social interactions could be a fundamental step in creating bonds that last years in vampire bats--some unrelated pairs have been found to travel together for more than a decade.

"The idea of using low-cost behaviors to build up to higher-cost investments can be something of much more general importance outside just food sharing in vampire bats," says Carter. This idea could be applied to other social animals such as primates and could provide insight into how humans build relationships.

For next steps, Carter wants to better understand how bats assess and choose their partners. "When two bats are unfamiliar, we have the opportunity to make a good partner or a bad partner and really see how that affects how the relationships form," he says. "So what we're trying to do now is use a variety of methods to really manipulate the relationships."
Current Biology, Carter et al.: "Development of new food-sharing relationships in vampire bats"

Current Biology (@CurrentBiology), published by Cell Press, is a bimonthly journal that features papers across all areas of biology. Current Biology strives to foster communication across fields of biology, both by publishing important findings of general interest and through highly accessible front matter for non-specialists. Visit: To receive Cell Press media alerts, contact

Cell Press

Related Relationships Articles from Brightsurf:

Gorilla relationships limited in large groups
Mountain gorillas that live in oversized groups may have to limit the number of strong social relationships they form, new research suggests.

Electronic surveillance in couple relationships
Impaired intimacy, satisfaction, and infidelity in a romantic relationship can fuel Interpersonal Electronic Surveillance (IES).

'Feeling obligated' can impact relationships during social distancing
In a time where many are practicing 'social distancing' from the outside world, people are relying on their immediate social circles more than usual.

We can make predictions about relationships - but is this necessary?
'Predictions as to the longevity of a relationship are definitely possible,' says Dr Christine Finn from the University of Jena.

Disruptions of salesperson-customer relationships. Is that always bad?
Implications from sales relationship disruptions are intricate and can be revitalizing.

Do open relationships really work?
Open relationships typically describe couples in which the partners have agreed on sexual activity with someone other than their primary romantic partner, while maintaining the couple bond.

The 7 types of sugar daddy relationships
University of Colorado Denver researcher looks inside 48 sugar daddy relationships to better understand the different types of dynamics, break down the typical stereotype(s) and better understand how these relationships work in the United States.

Positive relationships boost self-esteem, and vice versa
Does having close friends boost your self-esteem, or does having high self-esteem influence the quality of your friendships?

Strong family relationships may help with asthma outcomes for children
Positive family relationships might help youth to maintain good asthma management behaviors even in the face of difficult neighborhood conditions, according to a new Northwestern University study.

In romantic relationships, people do indeed have a 'type'
Researchers at the University of Toronto show that people do indeed have a 'type' when it comes to dating, and that despite best intentions to date outside that type -- for example, after a bad relationship -- some will gravitate to similar partners.

Read More: Relationships News and Relationships Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to