Vampire bats form long-lasting friendships by sharing blood with their roostmates, scientists have found.
The only known mammal to feed on blood, these bats have been found to split their meal with strangers by regurgitating it, in an act that resembles "a sort of French kiss".
Researchers say, their findings, published in the journal Current Biology, show bats can form life-saving bonds through social grooming and food sharing, similar to humans.
Gerald Carter, a behavioural ecologist and assistant professor at Ohio State University in the US and lead author on the study, said: "We go from bats starting as strangers from different colonies to groupmates that act to save each other's life.
"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 get their food by biting into large animals such as cattle.
These creatures run the risk of starving if they are unable to feed for three days.
Prof Carter said: "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."
To find out more about their food habits, the researchers gathered 30 bats from two different locations in Panama and introduced them to each other in groups or pairs in a lab setting.
For each group, the research team withheld food from one of the bats and observed how it interacted with its roostmates.
Over a course of 15 months, many of the bats, especially those in pairs, began grooming one another, which eventually led to sharing blood with those who were underfed.
Prof Carter said: "Even if you remove all ectoparasites from their fur, they still groom each other more than necessary for just hygiene.
"We think of social grooming as a kind of a currency - a way to gain tolerance and bond with another individual."
The team are now looking to better understand how bats assess and choose their partners in the next step of their research.
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