Experts study the social science of Wharfedale bats

Wharfedale Observer: A Daubenton's bat skimming the water (Picture: F Greenaway ©) A Daubenton's bat skimming the water (Picture: F Greenaway ©)

An Ilkley man and university professor has released interesting findings after monitoring bats along the River Wharfe.

Professor John Altringham, at The University of Leeds’ School of Biology, has led a team studying the population of several hundred bats along a 50km stretch of the river, for more than a decade.

They monitored roosts in Ilkley, Addingham and upstream to Grassington and higher still in the villages of Kettlewell and Buckden.

The researchers found that the 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 existence in roosts at the top of the dales.

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

Professor Altringham said: “Low down the dale, the females appear not to tolerate males 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. But it is also possible that the males choose not to roost with the females.”

Looking at the nursery colony in Ilkley, he said that the mothers and pups often have a lot of extoparasites, which are 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 said: “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.”

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 seven 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 life cycle.

Visit dx.plos.org/10.1371/journal. pone.0054194 to download the paper.

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