It found that when the vampire bats became isolated in a roost, pairs unfamiliar with one another - but in close proximity - would begin grooming, then "mouth-licking" before swapping food.
"We go from bats starting as strangers from different colonies to groupmates that act to save each other's life," said Prof Gerald Carter, author of the study and behavioural ecologist at Ohio State University.
"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.
"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," Prof Carter said.
Vampire bats establish friendships by sharing regurgitated blood with their neighbours in a "kind of horrifying French kiss", a new study says.