Fanging out: why do vampire bats groom each other so often?

New research shows social grooming and food sharing are more common adaptive traits in vampire bats than other species.

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A new study has shown social grooming behaviour is more prevalent in vampire bat species than their non-parasitic variants. The researchers used the species Desmodus rotundus and found that the bats spent 1.5-6.3 per cent of their time engaged in social grooming, compared with just 0.5 per cent in other species.

It's not exactly a secret that a range of animals engage in social interactions. This includes hyenas who simply greet each other to increase cooperation. However, recent studies have focussed on the use of social grooming being used by animals to maintain stable relationships.  

For example, age and body weight have been linked to the amount of social grooming given by dairy cows, and licking and head rubbing are used by lions to create bonds between individuals. Vampire bats also protect each other against bats with no social links to a group. Each roost site usually contains 8-12 female adults and their offspring, defended on the outside by an adult male.

Vampire bats not only show social grooming through the cleaning of each others' bodies, but also by sharing food through the ever-appetising regurgitation process. However, both of these behaviours are directly linked to one another.

When a pair of vampire bats are grooming each other and cleaning each other's bodies, they assess the bulging size of the abdomen. This allows them to check if their partner has eaten, and whether they need to regurgitate and share food.

Sharing food is a vital part of feeding and cooperation in vampire bats, as almost 20 per cent of bats don't find any food each night. This starts a ticking clock, as most bats can starve to death in under 72 hours.

The importance of social bonding is reflected in the anatomy of the bat. In proportion to their relatively small body size, vampire bats have a very large brain and neocortex. Previous studies have shown the size of the neocortex is linked to more complex social behaviour and bonding.

The authors of the paper conclude that social grooming acts as a way for bats to display their hunger to partners, or alternatively, that they are willing to share food, and for the need to sustain close bonds.

Emad Ahmed writes about science and gaming. He tweets @ThisIsEmad.