(CNN) Vampire bats may be bloodsucking creatures of the night -- but they also form strong friendships and help each other out in times of need, a study has found.

The study, published in the journal Current Biology on Thursday, found that vampire bats who formed social bonds in captivity maintained those bonds even after they were released back into the wild.

This is significant because it's often difficult to tell whether "partner fidelity" in animal relationships is due to the immediate costs and benefits of helping each other, or due to some shared relationship history. But in this experiment, the bats remembered and helped each other in two drastically different environments, even when they didn't have to.

The study, conducted by researchers at Ohio State University, housed 23 wild female vampire bats and their captive-born offspring for almost two years. To encourage them to help each other and to measure these relationships, researchers withheld food from some individual bats "to induce social grooming and regurgitated food sharing."

They found that the bats who didn't receive food had a higher probability of being groomed and fed by other bats. This kind of cooperation is particularly rare between vampire bats that aren't related because they have to pay a cost to help their peers -- to feed each other, they have to regurgitate their own meals.

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