What lies beneath in the caverns of the Dales

I mean, folks talk about the incredible radar that's on modern submarines and aircraft, but it's nothing compared to what bats have built into them at birth."David mentions Ease Gill – the longest and most complex cave system in Britain – near Kirkby Lonsdale. There are about 47 known miles of passage there, some of them so tight that cavers are barely able to squeeze through, and others only passable by humans with the use of diving equipment. And yet, he says, bats have been found in every inch of this vast subterranean labyrinth.

In the last couple of years David has begun to use technology that is almost as sophisticated as the bats' own inbuilt sonar, to learn more about their use of potholes. With recently developed monitoring equipment, supplied by Natural England, he is able to log the precise movements of bats in Dales potholes.

Most cavers are mainly interested in the geology and exploration aspects of potholes. But David, 68, a Craven Pothole Club member and retired biologist who lives at Settle, is one of less than half a dozen cavers in England to study underground wildlife. And for 50 years he has been recording the bats, spiders, worms, moths, ferns, lichens and other troglodyte life found in the darkest corners beneath the Yorkshire Dales.

He has been concentrating his efforts at two potholes. One of them is Bar Pot, on the slopes of Ingleborough in the Three Peaks area. This is the usual access point used by cavers wishing to see the spectacular underground cathedral-sized cavern of Gaping Gill.

In association with Professor John Altringham of Leeds University's School of Biology, his work has led to the discovery of the remarkable life cycle of a colony of up to 70 scarce natterer's bats at Bar Pot.

They have found that the bats raise their young in the village of Long Preston, some 25 miles east along the A65, and then in late-summer leave this maternity roost to spend each winter deep underground at Bar Pot.

"We know this because we netted many of the bats at both Long Preston and the entrance to Bar Pot and fitted them with identification rings. Later, we caught two ringed individuals at each location. We don't yet know what triggers their sudden departure from the Long Preston maternity roost to their hibernation quarters at Bar Pot. There also appears to be a gap of a week or two before they turn up at the cave entrance, so we would like to find out what happens to them during that period."

Besides the natterer's bats, four other species of bats have been discovered at Bar Pot – brown long-eared, whiskered, Brandt's and Daubenton's.

David has also set up the electronic bat logging devices at another pothole, Scoska Cave near Arncliffe in Littondale.

The cave was chosen because bats have been found to be active in their supposed hibernation period there, feasting on moths which have themselves gone to Scoska to spend the winter.

David has found a colony of the rare tissue moth living inside the cave. Moth recorders in Yorkshire usually find just one or two tissue moths a year, but, remarkably, he has counted more than 200 of them together inside Scoska.

They move into the cave in early August, and don't start leaving again until late-April, and during that time they are suspected of finding food sources deep underground.

"I'm trying to identify the food source," David says. "Condensation water on the cave walls may have some nutrients. It's possible that bacteria in the water breaks down to form a slime which contains a sugar that is attractive to the moths."

The full story of the tissue moths in Scoska Cave is still emerging. After counting 262 there in 2006 David went back to do another survey and tallied just 58. The huge discrepancy was explained when he found large number of moth wings littering the cave floor.

Bats which had gone there to hibernate had decided to top up their fat reserves by snacking on the moths.

"It's all part of the cave's fascinating ecosystem. The moths are surviving in the cave, we think, by finding a food source, and when they move about inside the cave to feed they are detected by the bats, which are then presented with a meal – virtually on a plate – without having to leave their hibernation site."

Other wildlife found in Scoska includes thousands of a species of mosquito known as Culex pipiens, and a spider called Meta merianae. Both of these also seem to be providing more food for bats.

David's bat monitoring equipment logs every time a bat goes past its sensor, so that he can build up a picture of how active they are feeding inside the cave when they are supposed to be in hibernation.

To get the information from his equipment David has to return to the cave ever four to six weeks and descend the system to download the data onto a laptop. Natural England's Andrew Hinde says that David's work is providing a unique insight into the wildlife of the Yorkshire Dales cave systems.The caves have been designated Sites of Special Scientific Interest (SSSIs) but when they are wet through most potholers don't take the time to look at things like spiders and flies.

"Our knowledge of the geology in what I call the Dark Zone is very thorough," Andrew says, "but surprisingly little is known about the creatures that live down there. I don't think anybody has been studying the biology of the Dales caves for as long as David. He's a real goldmine of information."