(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.
"It's pretty rare outside of humans to have behaviors where I'm paying an obvious cost to help you and you're not related to me," said Gerald Carter, one of the study's lead authors, in the press release.
Then, the bats were released back into their original roost, wearing small sensors to monitor their behavior. Even though they were now part of a bigger group with other bats who hadn't been part of the experiment, the "test" bats who had lived together in the lab stuck together -- they had higher levels of social grooming, food sharing, and close contact with each other.
The fact that the bats continued their friendships in the wild was "a sign that the relationships weren't borne only of convenience while they lived together in a cage," said the study's press release.
"It's kind of analogous to being friends in high school," said Carter. "After you graduate, and you're released out of this structured environment, do you continue to stay in touch with those people, or do you lose touch with them? It depends on personality types and the kinds of experiences you shared. That's essentially what we were after with this study."
The study concluded that, much like humans, vampire bat friendships are generally strengthened by their shared past experiences.
However, sometimes humans drift apart after high school -- and similarly, not all the lab bat friendships survived in the wild. In particular, the captive-born offspring had bite marks after returning to the wild colony, and they eventually left the roost. The study suggested they might have tried to fly back to their place of birth -- the lab -- or perhaps failed to develop natural wild bat behaviors.