Vampire bats who roost together tend to forage for blood together too, study finds 

It isn’t just humans who like to go out for dinner with friends, according to a new study, that found female vampire bats go out foraging for blood with their mates. 

Animals that form bonds in captivity and continue those friendships in the wild also hunt together, according to researchers from Ohio State University in Columbus.

The team attached tiny senors to 27 wild and 23 captive female vampire bats, before releasing them back into their wild roost on a cattle pasture in Tole, Panama.

They found that when roosting together in trees the bats have been seen grooming each other, sharing meals and meeting up to forage even after leaving the root.

Study co-author Gerald Carter and colleagues wanted to find out whether social bonds formed between bats also influenced foraging behaviour.

The professor of evolution, ecology and organismal biology said they looked at the possibility of different scenarios for their behaviour.

‘We found that they leave the roost to forage independently of each other, but then the ones that have a relationship are somehow finding each other and associating out on the cattle pasture – and we think they’re coordinating,’ said Prof Carter.

The 50 female bats, Desmodus rotundus, wore backpack computers as they were released to their usual roosting site, or from captivity.

While the tagged bats almost never left the roost together, closely bonded females often reunited far from the roost, the study found.

The animals that associated with more partners in the roost also met up with more partners during foraging trips.

They essentially found that bats with a large group of friends are more likely to continue to meet up with those friends when out finding food.  

They hypothesise the bats may meet up with trusted partners during foraging trips to share information about hosts or access to an open wound for feeding.

It is suggested this collaboration might save on the time and effort involved in selecting and preparing a wound site on the cattle.

Bats that spent more time near each other in the roost during the day also spent more time together outside at night and encountered each other while foraging more frequently than bats not showing signs of social bonds. 

Foraging encounters between bats that had close relationships were, on average, longer in duration as well.

‘If you think about it, a longer interaction is more likely to be cooperative or affiliative than a short encounter, which could be neutral or aggressive,’ Simon Ripperger, a former postdoctoral researcher in Carter’s lab, explained.

Audio recordings of vampire bat calls in La Chorrera, Panama, where this study took place, revealed three distinct call types made by the flying mammals.

These were: downward sweeping social calls, antagonistic buzz calls, and n-shaped feeding calls, with the last of them not previously observed in vampire bats. 

They may be able to identify friends and foes while flying using the downward sweeping calls, which are similar to contact calls used to recognise partners in the roost. 

The findings prompted the researchers to question ‘how far ‘friendship’ goes’.

‘We show that social bonds of vampire bats are not restricted to grooming and food sharing at the roost, but bonded individuals even hunt together, highlighting the complexity of their social relationships.’

The study is published in the Plos Biology journal.