Vampire bats form bonds of ‘friendship’ that last beyond captivity

Vampire bats are known for their bloodthirsty cravings, but a new study suggests the mammals have a warm and fuzzy side: When they become “friends” in captivity, their batty bonds stay strong even after they are released into the wild.

To test the strength of relationships in female common vampire bats (Desmodus rotundus), which often groom and share food (normally the blood of livestock) with one another, researchers caught 17 bats from a wild colony and kept them—and their six offspring—in captivity for nearly 2 years. At intervals, they stopped feeding individual bats for 26 to 28 hours. When they reintroduced the hungry bats to the group, their better-fed companions groomed them and shared partially digested food with them. Over time, some of the bats seemed to form “friendships,” in which they consistently groomed and exchanged food with the same few partners.

Finally, researchers outfitted the bats with tiny trackers and released them to join an existing colony roosting in a hollow tree. The researchers also outfitted 27 wild bats from the colony with their trackers, and then monitored their social interactions for 8 days.

Many of the previously captive bat “friends” continued to hang out, roosting near one another instead of randomly among the hundreds of other wild bats, the researchers report today in Current Biology. This loyalty means the bats’ relationships were likely more than just a side effect of their close quarters in the lab, the researchers say.

Still, some bonds dissolved over the study period, especially those between captive bats that had originally been wild and those that had been born in the lab. Most of the captive-born bats also chose to roost outside the tree and some showed bite marks and signs of fighting with other bats, which suggests they may have been social outcasts in the wild bat colony. After just 6 days, all the captive-born bats had left the hollow tree for greener—or perhaps bloodier—pastures.