Monday, 7 April 2008

"Untold riches" of swarming bats...

I am officially conferenced out, having spent the last three days in York for the
Mammal Society Conference. It was definitely worth going: I'm buzzing with thoughts about Irish hares, Beaver management in Bavaria, small mammal survey trials and much else besides. It's a little disappointing that there were no papers on bats, but that was more than made up for by Professor John Altringham's Cranbrook lecture.

John's team from Leeds University have carried out a large and complex study of bat swarming behaviour at caves in the Yorkshire Dales and the North Yorkshire Moors. Autumn swarming is a behaviour which is increasingly seen as an important part of the annual cycle of bats, especially Myotis and Long-eared species. Bats gather at hibernation sites, usually caves and mines, to check out the site, to help young bats find it and for courtship and mating. Swarming is typified by chasing behaviour late into the night, often peaking three or four hours after sunset and takes place during August to October.

They looked at Natterer's Bats (Myotis nattereri) and, by ringing bats at known summer maternity roosts and then harp trapping at swarming sites, were able to demonstrate that bats wer flying up to 60km to a swarming site. They were also able to demonstrate that huge numbers of bats were using these sites: up to 400 per night, with considerable turnover between nights. Furthermore, by comparing data year on year they were able to demonstrate high fidelity: bats tend to return to the same site each year. The conservation implications are huge: these sites can provide a key part of the lifecycle of very large numbers of bats, from a wide geographical area.

What struck a chord with me was the fact than John described the importance of these sites and went on to mention that it was then usual to find only a handful of hibernating bats within the caves, as many were not visible. In other words, some of the hibernation sites we survey in the Scotland could be swarming sites for similarly large numbers of bats. Not for nothing was one of John's conclusions the possibility of "untold riches" for bat-workers.

This tiny hole, high in the hills in South-west Scotland, gives access to a tunnel over half a kilometre long, which contained 9 Natterer's Bats and 1 Daubenton's. Could this be a swarming site on a similar scale to the ones in the Yorkshire Dales?

Another intriguing part of the lecture related to a study in which John's team compared the numbers of hibernating bats to the physical features of a cave or mine. They found that the size of entrance was irrelevant ("if you can get in, they will"), as was the altitude, the orientation of the entrance and the habitat nearby. What makes a good hibernaculum is large spaces inside, a reasonable depth, some cover near the entrance and not too wet. This struck a chord with me, as we've done several surveys in the past winter of a limestone mine, which seemed to have all the right features of a hibernaculum, but we never found any bats. John's conclusion was "the more water, the fewer bats", which seems to fit.

I must finish by plugging the Mammal Society's new edition of "The Mammals of the British Isles". It's not cheap (and you may need to reinforce your bookshelf to take the weight), but it is worth every penny. If you buy a copy via the Mammal Society website, all ofthe profit will go to the society.

John Altringham's Leeds University web-page:

The Mammal Society:

My website:

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