Bite to eat? Vampires prefer feeding in company, research reveals

Disregarding their unappealing habit of sucking blood from live victims, vampire bats increasingly appear to be emerging as a challenger to humans in their efforts at operating a civil society, with recent research revealing an extraordinary level of cooperation and resourcefulness among colonies.

These include: members of the species self-isolating when ill, mothers adopting orphan babies, females sharing food equally, and grooming taking place within an egalitarian social framework.

The latest study into the species has now revealed that when female bats eat, they prefer to do so in company.

During their nightly foraging trips, in which they seek out live prey on which to feed, female vampire bats preferentially meet up with other individuals they have close social bonds with, according to researchers from the Ohio State University and the Smithsonian Tropical Research Institute in Panama.

The research team suggested the bats may meet up with trusted partners during foraging trips in order to share information about hosts or access to an open wound.

They speculate that this collaboration might save on the time and effort involved in selecting and preparing a wound site on the cattle.

In order to track what the bats were up to, the researchers attached tiny “backpack” computers to 50 vampires – some that had previously been in captivity together and others that had lived only in the wild – to track their movement during their nightly foraging outings.

By day, the bats shared a hollow tree in Panama, and at night they obtained their meals by drinking blood from wounds they made on cows in nearby pastures.

The tracking data revealed the vampire bats tended to set out to forage separately rather than as a group. However, once they had left, those individuals which had established social relationships would reunite during the hunt for what the researchers suggested was some sort of coordination over food.

The team said their findings suggest “making friends” in the roost could create more interdependence among socially bonded vampire bats – meaning they could benefit from each other’s success at obtaining blood meals and join forces when competing with other groups of bats for food resources.

“Everything we’ve been studying with vampire bats has looked at what they’re doing inside of a roost,” said study co-author Gerald Carter, an assistant professor at the Ohio State University.

“What nobody has really known up until now is whether these social relationships serve any function outside the roost,” he said.

“Understanding their interactions with a completely different group of bats out on the pasture can help us understand what’s going on inside the colony. If every time they leave the roost they’re getting into battles, that can increase the amount of cooperation within the colony.”

The team supplemented the tracking data by capturing video and audio of foraging vampire bats.

Thai included footage of bats clustered together on one cow and others atop separate cows, some drinking from different wounds and some fighting over food access.

The team also made what they say are likely the first audio recordings of a specific type of vampire bat vocalisation associated with foraging.

The recorded vocalisations may eventually provide other insights about vampire bats’ social behaviours. Downward sweeping calls inside roosts, and “buzz” calls during arguments had been documented before, but the calls recorded during the hunt, which increased and then decreased in frequency, were distinct from those.

“I could see them vocalise even if they were alone on a cow, and they vocalise back and forth, so we can tell that they interact while they’re feeding,” said co-author Simon Ripperger.

The research is published in open-access journal PLOS Biology.