Bats split on family living

Jan 24, 2013
Daubenton's bat. Credit: Wikipedia

For the tiny Daubenton's bat, the attractions of family life seem to vary more with altitude than with the allure of the opposite sex.

For more than a decade, a team led by Professor John Altringham from the University of Leeds' School of Biology has studied a population of several hundred along a 50-km stretch of the River Wharfe. They monitored roosts in Ilkley and Addingham, upstream in the market town of Grassington and higher still in the villages of Kettlewell and Buckden.

The researchers found that all Daubenton's bats in nursery roosts in lowland areas of Wharfedale during the spring and summer were females and their offspring.

Male bats were mostly restricted to a windier, Heathcliff-like existence in roosts at the top of the Dales.

But the researchers were surprised to find a small oasis of in Grassington, sandwiched between the bustle of the women-only childrearing in the and the more relaxed lives of the bachelors in the highlands.

Professor Altringham said: "Low down the dale, the females appear not to tolerate and we assume they won't let them in the roost. They don't want anything to do with them. High in the dales, all the roosts are bachelor pads. But in the middle, at Grassington, males and females live together—the social structure changes with the environment"

"One possible reason for not finding males low down the valley could be that the mothers just want to avoid competing with males for food. It takes a lot of insects to make the milk needed to feed their young," Professor Altringham said.

"But it is also possible that the males choose not to roost with the females. When you look at the nursery colony in Ilkley, mothers and pups often have a lot of ectoparasites like ticks and mites. In a warm, crowded nursery, parasites can thrive, especially if there's less time for good personal hygiene. Parasites not only make life uncomfortable but can affect a bat's health. The males that live by themselves are usually very clean in their bachelor pads, so you can understand why they might not want to move in," he added.

At Grassington, which is deep in the Yorkshire Dales National Park but not as high as Buckden and Kettlewell, the bats have a completely different . Both male and female bats live with the young throughout the spring and summer in roosts in the stonework of the old Dales bridges and in holes in ash trees.

"Females may roost as high up the dale as Grassington because they have these warm, cuddly males to bunk up with. This way, females use less energy keeping warm and babies grow faster," Professor Altringham said. "In these marginal conditions, they may just tolerate a few males to keep them warm. Otherwise they kick them out. Why do the males co-habit if they are going to get parasites all over them? Well, that may be down to the usual answer: sex."

Although male and female Daubenton's bats usually live apart throughout the spring and summer, they meet when they begin flying to caves in late summer.

Professor Altringham said: "In and around these caves the bats gather in huge numbers to mate, in a behaviour known as swarming. This is clubbing for bats, with males displaying to females in lengthy acrobatic chases. As winter closes in, these caves will ultimately be their hibernation sites.

"There are nearly 2,000 cave entrances and hundreds of kilometres of cave passages in the Dales and these attract bats from all over Yorkshire, Lancashire, Cumbria and beyond for mating and hibernation. The males in Grassington may be giving themselves the opportunity to mate with the females late in the summer before they even get to the caves."

The researchers have built up a detailed picture of social and sexual behaviour by genotyping hundreds of individuals. The evidence gathered from this supports the theory that the Grassington males enjoy an advantage in mating.

"At Grassington, most of the fathers of bats born there spent the summer with the females. If we look at pups in Addingham and Ilkley, their dads were males caught when swarming at caves. So, as well as two different mating systems, you have distinct social groupings. A bachelor from Buckden is always a bachelor from Buckden. He doesn't pop down to Grassington to visit the females in the summer. His only option seems to be to go clubbing in the autumn," Professor Altringham said.

The Daubenton's bat, named after the 18th Century French naturalist Louis-Jean-Marie Daubenton, is widespread across the United Kingdom and specialises in hunting insects over water. Full-grown adults weigh only 7 to 12 grams, but they can live for 20 years or more.

"These bats are the size of a shrew but have a very different lifecycle. A shrew typically spends its entire life in a few metres of hedgerow, eats and breeds with a ferocious intensity, for a year if it is lucky, and then dies. In contrast, these bats lead a complex life over a huge area and produce only one pup a year," Professor Altringham said. "This makes bats particularly vulnerable to the problems of habitat fragmentation and climate change."

Explore further: Male monkey filmed caring for dying mate (w/ Video)

More information: Ruth L. Angell, Roger K. Butlin and John D. Altringham. 'Sexual segregation and flexible mating patterns in temperate bats,' PLOS ONE, DOI: 10.1371/journal.pone.0054194

Related Stories

Hibernation keeps rabies going in bats

Jun 07, 2011

(PhysOrg.com) -- In a new study published in the Proceedings of the National Academy of Sciences, infectious disease biologist Dylan George from Colorado State University reports that a bat’s hibernation is wha ...

Bats keep separate households

Mar 24, 2011

(PhysOrg.com) -- The use of different resources by males and females exacerbates the estimation of population sizes. However, the monitoring of population sizes, particularly for rare and threatened species, ...

Mating that causes injuries

Feb 20, 2009

Researchers at Uppsala University can now show that what is good for one sex is not always good for the other sex. In fact, evolutionary conflicts between the two sexes cause characteristics and behaviors that are downright ...

Early spring means more bat girls

May 05, 2012

There must be something in the warm breeze. A study on bats by a University of Calgary researcher suggests that bats produce twice as many female babies as male ones in years when spring comes early.

Recommended for you

Male monkey filmed caring for dying mate (w/ Video)

9 hours ago

(Phys.org) —The incident was captured by Dr Bruna Bezerra and colleagues in the Atlantic Forest in the Northeast of Brazil.  Dr Bezerra is a Research Associate at the University of Bristol and a Professor ...

Orchid named after UC Riverside researcher

Apr 17, 2014

One day about eight years ago, Katia Silvera, a postdoctoral scholar at the University of California, Riverside, and her father were on a field trip in a mountainous area in central Panama when they stumbled ...

In sex-reversed cave insects, females have the penises

Apr 17, 2014

Researchers reporting in the Cell Press journal Current Biology on April 17 have discovered little-known cave insects with rather novel sex lives. The Brazilian insects, which represent four distinct but re ...

Fear of the cuckoo mafia

Apr 17, 2014

If a restaurant owner fails to pay the protection money demanded of him, he can expect his premises to be trashed. Warnings like these are seldom required, however, as fear of the consequences is enough to ...

User comments : 0

More news stories

Researchers successfully clone adult human stem cells

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...

Plants with dormant seeds give rise to more species

Seeds that sprout as soon as they're planted may be good news for a garden. But wild plants need to be more careful. In the wild, a plant whose seeds sprouted at the first warm spell or rainy day would risk disaster. More ...

Researchers develop new model of cellular movement

(Phys.org) —Cell movement plays an important role in a host of biological functions from embryonic development to repairing wounded tissue. It also enables cancer cells to break free from their sites of ...

Male monkey filmed caring for dying mate (w/ Video)

(Phys.org) —The incident was captured by Dr Bruna Bezerra and colleagues in the Atlantic Forest in the Northeast of Brazil.  Dr Bezerra is a Research Associate at the University of Bristol and a Professor ...