Vampire bats, it seems, embrace what you could think of as social distancing.
A new study published in the journal Behavioural Ecology suggests that when they are sick they spend less time near others from their community, which slows how quickly a disease will spread.
The research team, led by Ohio State University, US, had seen this behaviour in the lab, and used a field experiment to try to confirm it in the wild.
Simon Ripperger, Gerald Carter and Sebastian Stockmaier captured 31 female common vampire bats (Desmodus rotundus) living inside a hollow tree in Lamanai, Belize. They injected 16 with an immune-challenging substance, and the rest with saline.
They then fitted them with proximity sensors, returned them to their tree, and tracked activity over three days. This included an initial “treatment period” from three to nine hours after the injections during which they attributed behaviour changes to the effects of treated bats feeling sick.
On average, the sick bats associated with four fewer groupmates over the six-hour treatment period and spent 25 fewer minutes interacting per partner. The time any two bats spent near each other was shortest if the encounter involved at least one sick bat.
These differences declined after the treatment period and when the bats were sleeping or foraging outside the roost.
One reason, no doubt, was that sick bats felt lethargic and moved around less: but the outcome, Carter says, was the same. “These simple changes in behaviour can create social distance even without any cooperation or avoidance by healthy bats.”
The effects are probably common in many other animals, the researchers says, though actual behaviour changes would depend on the pathogen. And it seems they are well equipped to find out more.
“The sensors gave us an amazing new window into how the social behaviour of these bats changed from hour to hour and even minute to minute during the course of the day and night, even while they are hidden in the darkness of a hollow tree,” says Ripperger.
“We’ve gone from collecting data every day to every few seconds.”