Bats that shared blood and groomed each other preserved their ties even after a change of residence.

Much like many primates, vampire bats can form strong bonds with each other and often maintain these friendships even after being uprooted.

To document this behaviour, Gerald Carter at the Ohio State University in Columbus, Simon Ripperger at the Leibniz Institute for Evolution and Biodiversity Science in Berlin and their colleagues captured 17 female common vampire bats (Desmodus rotundus) from a colony living in a tree in Panama. The animals were kept in a lab and repeatedly denied food. This caused the bats to groom each other and share snacks of regurgitated blood, behaviours that signal cooperation and social bonding.

After 22 months, the 17 bats and their 6 captive-born daughters were equipped with sensors and released back to the original colony. The researchers observed that the females that had befriended one another in captivity generally preferred to roost closer to each other than to bats that had not been in the captive group.

Not all of the relationships survived, however. And all of the lab-born bats left the original colony a few days after release, perhaps because they failed to integrate with the group.