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Vampire bats are BLOOD DONORS: Mammals share meals with friends to boost the survival chances of the overall group

Researchers recorded female vampire bats showing 'reciprocal altruism'
Successful female hunters share blood with hungry group members
Behaviour suggests the social lives of bats are more complex than thought

Published: 05:34 EST, 18 November 2015 | Updated: 05:57 EST, 18 November 2015

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They may be depicted as terrifying and aggressive in horror films but vampire bats are much more altruistic in real-life.

Researchers have discovered that females 'donate' blood they have taken from their prey to other members of the group to make sure they don't go hungry if they have missed a meal.

The behaviour suggests the bats' social lives are more complex than previously thought.

They may be depicted as aggressive and terrifying in horror films, but vampire bats (stock image) are generous in real life. Researchers have discovered that females 'donate' blood they have taken from their prey to other members of the group to make sure they don't go hungry if they have missed a meal

The maligned species eats only blood by taking small amounts from hosts – usually livestock - without harming them.

It is not thought to be painful, with the bats using their razor-sharp incisors to remove skin and leave a wound likened to a 'golfer's divot' behind.

The anti-coagulant in their saliva allows the blood to flow, and they 'lap it up like a cat with a saucer of milk', according to nature writer Simon Barnes.

On a successful forage, the mammals can take a meal of half their own body weight and their bodies are finely tuned to their strange hunting technique, enabling them to sense body heat.

The behaviour suggests the bats' social lives are more complex than previously thought

Living in tightly-knit communities, females, which typically measure 4-inches (10cm) long with a 7-inches (18cm) wingspan, huddle together to keep themselves and their pups warm, as well as safe from predators.

Some colonies are huge, with up to 2,000 animals, but most are smaller and rely on a core number of female members.

The mothers care for their young for nine months – around eight months longer than other bats – and they now also seemingly look out for each other.

In particular, females share regurgitated blood with others that have not managed to secure a meal themselves to stop them starving which can take as little as two days, National Geographic reported.

Such behaviour, known as reciprocal altruism was first reported in the 1980s.

A researcher at the Smithsonian Tropical Research Institute in Panama has now collected evidence of this behaviour by observing captive populations of vampire bats at the Organisation for Bat Conservation in Michigan.

Gerald Carter recorded their habits for three years using a night-time camera to note that the creatures often share their meals.

To see this behaviour, he took some bats' food away for 24 hours before reintroducing the hungry creatures to their group.

He then recorded when bats offered bloody vomit to others - an experiment he repeated hundreds of times.

Carter noticed if a hungry female had previously shared blood with others, she received a larger donated meal than a more 'selfish' bat.

During tests, if a hungry female had previously shared blood with others, she received a larger donated meal than a more 'selfish' bat. While some bats refused to help self-centred hungry individuals (stock image)

While some bats refused to help self-centred hungry individuals.

This tat-for-tat behaviour was further complicated because those that had refused to share their food previously were even more generous than their peers at a later date.

Carter likened this behaviour to being 'especially generous to a friend if you were unable to help them for a long time'.

The study, published in Proceedings of the Royal Society B, suggests female vampire bats keep track of those in the group they can rely on in times of need and repair broken relationships.

BATS HAVE HEAVY WINGS TO LET THEM PERFORM MID-AIR ACROBATICS

They are perhaps the most manoeuvrable creatures in the animal kingdom, able to perform mid-air aerobatics to snatch insects and flip upside-down to hang off cave ceilings or branches.

But bats agility in the air may be down to something that other flying animals have attempted to avoid – heavy wings.

While most birds and insects have evolved lightweight wings to help them stay aloft, the long extensions of skin, tendons and bone in bats are heavy compared to their body size.

Bats use the inertia created by their heavy wings to help them perform mid-air acrobatics, allowing them to twist around so they can land upside down on roosts. The researchers used high speed cameras (top line of pictures) and computer simulations (bottom row) to study how the animals managed to flip in the air

However, it appears these could be the mammal's greatest assets, as scientists have found they use the extra weight in very precise ways to help them turn.

In many ways bats can be compared to modern jet fighters which use their instability in the air to give them extra manoeuvrability.

Professor Kenny Breuer, an engineer at Brown University, in Providence, Rhode Island, said the discovery could aid the design of new types of air craft.

He said: 'Normally you'd think that an animal would not want to have such massive wings. But here, it turns out that the mass can be used to some benefit.

'From an engineering perspective, there's a lot of interest in drones and flying microvehicles.

'Manoeuvring or directing those robotic vehicles is a challenge. The idea here is that using redistribution of mass is not a bad approach to take.'