Vampire bats live in female-dominated groups, and they appear to groom and share food with each other equally without regard for social status.
Unlike the “strict, obvious female dominance hierarchy” seen in many other social animals, the “egalitarian” social life of vampire bats suggests that individuals do well when their groupmates are doing well, says Gerald Carter at The Ohio State University.
“With vampire bats, grooming and food-sharing is very reciprocal, not one-sided like you might see in some primates,” Carter says. “They’re often grooming each other at the exact same time, for the exact same amount of time.”
Carter had been studying how female vampire bats cooperate, such as through social grooming and especially sharing food by regurgitating it. But when he saw primates interacting, he realised how different the social behaviours appeared.
“I was thinking, ‘vampire bats just don’t constantly harass and dominate other individuals almost for no apparent reason like these primates do’,” he recalls.
Carter and his colleagues decided to observe 24 wild-captured, adult, female common vampire bats (Desmodus rotundus) and their offspring – nine young bats including five females. All the bats were kept in a large cage in which they could fly around at the Smithsonian Tropical Research Institute in Gamboa, Panama. The team left drops of blood on the floor overnight for 70 nights and used infrared video to record more than 1000 interactions between the bats.
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On rare occasions, the bats would fight over the food by hitting each other with their thumbs, Carter says. Usually, though, the bats would just push one another out of the way, or voluntarily step away.
The researchers concluded that the bats have what they term a “weak and shallow” hierarchy.
They also looked at social hierarchies in 82 other species, including mammals, insects and birds, and found that the vampire bats’ hierarchy was so weak that it was less clearly defined than for 90 per cent of these other species.
Also unlike these other species, the female bats didn’t use grooming as a tool to appease individuals of a higher social rank, but rather they groomed and shared food evenly.
Carter admits his team might have missed signs of stronger social organisation in this “first step” of the ongoing research project, however. For example, the bats could use sounds out of human hearing range to show dominance.
But it is also plausible that because female bats share their food – which their bodies can’t store as fat – they might be interested in the well-being of their groupmates, especially as potential food donors.
“These bats don’t act out of harassment or bullying or some sort of force,” says Carter. “They’re voluntarily [grooming and] giving food to another bat, essentially saving her life.”
Journal reference: Royal Society Open Science, DOI: 10.1098/rsos.210266