Bat Sexes Alternate Between Cohabitation And Solitude
January 25, 2013

Bat Bachelors Change Habitat Depending On Season And Altitude

Brett Smith for - Your Universe Online

Family dynamics can vary from species to species. However, a new study from researchers at Leeds University shows that family dynamics among the tiny Daubenton´s bats living in the north of England can vary by altitude and season.

According to the U.K. researchers report in the open access journal PLOS ONE, the family dynamics of the Daubenton´s bats that live along a 31-mile stretch of the River Wharfe can be organized by altitude, with the spring and summer nursery roosts in lowland areas containing only females and their offspring, the highlands roosts being dominated by male bats, and a middle ground where the sexes and their offspring cohabitate.

“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,” said lead author John Altringham from the University of Leeds´ School of Biology. “But in the middle, at Grassington, males and females live together — the social structure changes with the environment."

In their report, the researchers theorized that the decreased availability of food in the higher elevations could play a role in why they are male dominated.

“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,” Altringham explained.

The Leeds professor also said that the male bats could be avoiding the females and pups in lowlands because of the relatively poor hygiene conditions in bat nurseries.

“In a warm, crowded nursery, parasites can thrive, especially if there´s less time for good personal hygiene,” he said. “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.”

Although male and female Daubenton´s bats usually live separate lives during the spring and summer, they begin to flock to mating caves in late summer.

“In and around these caves the bats gather in huge numbers to mate, in a behavior known as swarming,” Altringham said. “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.”

The biologists performed a genetic analysis of the bats that showed their social and mating habits are not accidental but are reflective of their local altitude and environment.

“At Grassington, most of the fathers of bats born there spent the summer with the females,” said Altringham. “If we look at pups in (the lowest elevations), 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,” the professor noted about bats living in the study´s highest elevations. “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.”