Vampire bats 'social distance' out in the wild when feeling ill © Getty Images

Vampire bats ‘social distance’ out in the wild when feeling ill

Six hours after getting ill, a sick bat had associated on average with four fewer friends than its healthy counterpart.

Wild vampire bats socially distance when they are sick, a new study suggests. Scientists had previously seen this behaviour in lab conditions, but wanted to find out if it occurred in the wild.

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The researchers captured 31 adult female vampire bats from a hollow tree in Lamanai, Belize. The team injected half the bats with lipopolysaccharide, a toxic substance known to make them sick, while the other half received saline injections.

The researchers then glued proximity sensors to the bats and released them back into their tree. Scientists were able to track changes over time in the associations among the 16 sick bats and 15 control bats.

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The animals that were ill spent less time near others, associated with fewer group mates and were less socially connected to those that were healthy, researchers found.

The study, published in Behavioural Ecology, found that in the six hours after injection, a sick bat associated on average with four fewer associates than a bat that had been injected with saline.

On average a control bat had a 49 per cent chance of associating with each control bat, but only a 35 per cent chance of associating with a sick bat.

They also found that these differences declined after the first six hours and when the bats were sleeping or foraging outside.

“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,” said the study’s lead author, Simon Ripperger, from the department of ecology, evolution, and organismal biology, at the Ohio State University.

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“We’ve gone from collecting data every day to every few seconds.”

Reader Q&A: Why do bats live in caves?

Asked by: Jasper Liddle, London

They do it to avoid danger and save energy. The largest bat colony, in Bracken Cave, Texas, is thought to contain 20 million bats. Some species use caves for daytime roosting; others hibernate there for the winter because caves provide optimal humidity, a stable low temperature, and few disturbances from light or noise.

Temperature is important because bats are warm-blooded but very small. Unlike other mammals, they let their internal temperature drop when they are resting, going into a state of decreased activity to conserve energy. Hibernation is an even deeper state of inactivity in which their body temperature drops to that of the cave.

A special adaptation allows bats to hang upside down for months without using any energy. A tendon from their talons is connected to their upper body, not to a muscle. So when they hang, the weight of their body holds them in place. They can then drop straight into flight when they wake up.

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