Size is everything, especially in bats

Posted on February 17, 2011

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All primates have large brains and that includes us. Although I seriously wonder sometimes whether this is true of some people. Yesterday, I had to reprimand a young man (I’m slowly but surely turning into father) in Vauxhall while crossing a busy main road. The numpty in question, decided the quickest route to cross three lanes of traffic, would be to walk diagonally, cutting into my path while looking the opposite way. Who does that? Doesn’t anyone get taught the Green-Cross-Code in school any more?!

Animals with large brains which includes primates, both non-human and us (with the exception of the numpty!) live in complex, dynamic social groups. The way large-brained animals interact with individuals is regarded by scientists as important in understanding the evolution of animal sociality, and that includes mankind. Elephants, dolphins, some carnivores and primates maintain long-term social links despite their communities frequently splitting up and coming back together – a phenomena known as fission-fusion dynamics.

These types of communities (fission-fusion) allow groups to adjust to different ecological demands without losing the benefits that come with grouping. Chimpanzees (Pan troglodytes) are known to live in these types of groupings which also resemble how people behave and form different friendships. Up until now, it was only assumed that large-brained animals did this. However a paper published in the Proceedings of the Royal Society B, has discovered that bats can also form similar social networks.

Bechstein's bats huddle on a roost in Germany

Co-author of the study, Professor Gerald Kerth of the University of Greifswald in Germany said: “Our study shows that animals with a peanut-sized brain, like these bats, can also have stable long-term relationships.”

Kerth and his co-authors (Professors Nicolas Perony and Frank Schweitzer of ETH Zürich in Switzerland) observed two colonies of wild Bechstein’s bats (Myotis bechsteinii) over a five-year period. Kerth et al say their study may shed light on the link between complex social groups and social cognition – the ability to learn about others within a group – in mammals.

Professor Perony told me: “What is interesting is that it teaches us that, in some regard at least, we (as primates) are not incredibly advanced as we often boast, since species with very limited cognitive abilities can also build complex societies like primates.”

The bats were monitored with microchips implanted in the first year of life, and a sample of wing tissue was collected for genetic identification. Over the five-year study their individual size, as well as yearly reproductive status was monitored.  Male bats of this species are solitary, but females roost together in bat boxes and tree cavities. They preferred certain companions over the years.

The results revealed surprisingly stable social sub-units in which both related and unrelated females formed long-term social bonds.  The researchers believe that human-like friendships are likely to exist among other bats living in temperate zones, since these bats often live in colonies that also frequently split and merge (fission-fusion).

Bechstein's Bat

Professor Kerth said: “How complex social systems function is a key question in biology, economics and social sciences. Answering it requires information about the structure and dynamics of the social network, which characterises the relationships among group members.

“We need more studies dealing with the question of where simple mechanisms are sufficient to maintain social complexity, and where high cognitive abilities are needed. It would be fantastic to know more about where the cognitive limits of the bats are, and what the benefits are of having stable social links in bats.”

Bats are not renown for their cerebral capacities – Bechstein’s bat brains are less than a quarter of a cubic centimetre in size. So how memory works, is something that needs more exploration.  Perony and Kerth believe it could be down to an individual’s scent, but this hasn’t been proven yet.

Professor Perony added: “If I don’t see my friends for two years and I meet them again I will still be able to remember who they are, so our friendship, our social bond, will be kept. This is not the case in many animal species, but it is for Bechstein’s bats.”

Building a complex society is usually thought to be very demanding in terms of cognitive abilities, hence why it was thought to be the domain of bigger brained animals.

Long-term data on such dynamics in wild mammals are scarce and but I’m sure if researchers need to observe more peanut-sized brained mammals I’d be happy to point them in the right directions of a few numptys in Vauxhall.

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