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In the bat of an eye

Outdoor Living

FAST MOVERS The common pipistrelle.

Country Sights and Sounds

John Shelley

I was happy to show our visitors around and recount a little natural history as we wandered along the shore of Lough Carra, pointing out various ducks and a pair of great-crested grebes.
“Are there bats here in the winter?” the youngest of the party wanted to know.
“Oh, no,” says I, “They’re fast asleep, hanging upside down by their feet with their wings tucked about them as if they were blankets.”
“Then what’s that?”
She pointed at a small dark shape that flickered along the tree line before turning at the waters edge and retracing its path until it flew briefly overhead. It was, of course, a bat, the appearance of which destroyed my credibility altogether. When I explained how it was probably hunting chironomids, insects that neither eat nor drink for their entire adult lives, I was met with a thoroughly disbelieving look.
Later that evening I dug out my books and found various references to winter bats. Back as far as 1777 Gilbert White observed it ‘worthy of notice that when the therm rises above 50 degrees Fahrenheit the bat wakens and comes forth to feed in every winter month’. We now know that the body temperature of hibernating bats is lowered close to the ambient temperature of the air around them. And, as White noted, once this rises to 50 degrees Fahrenheit (about 10 degrees Centigrade) they are stirred to life, and as their metabolic rate increases they need to eat.
This was the smallest of our bats, one of the pipistrelle family; its rapid and somewhat erratic flight and small size identified it as such. There was a time the pipistrelle was just a pipistrelle, regularly finding its way into the house on a summer evening to lead a merry band around the kitchen as we sought to return it to the outside world, where it would hunt at the window. Modern biological science has divided our ‘pips’ into three separate species, the common pipistrelle; the soprano pipistrelle, which squeaks in a slightly higher pitch; and the Nathusius’ pipistrelle, which is pretty much identical to its two cousins though less widespread. North-western populations of this latter bat are known to migrate to continental Europe for the winter and appear to be widening their range with each succeeding spring return.
It is only by means of a bat detector, a device used to measure the frequency of calls used for echolocation (the means by which bats are able to find their insect prey in darkness) that the presence of a particular pipistrelle species can be determined. These small machines are just the size of a mobile phone and much underused. Every school should have one. It is even possible to download a bat-detector app suitable for use on most mobiles, although these need an external microphone capable of picking up ultrasonic signals.
It was one summer’s evening that I first watched bats emerging from a crack in the external plasterwork of Moorehall. I heard them first, as a strange wind-like rustling accompanied by a musical squeaking – contrary to popular opinion bats can be heard, especially by younger ears. Just as the light started to fade the first of them began to emerge from the roost.
My initial reaction was one of amazement, that these creatures with a wingspan of almost ten inches could appear from all but invisible cracks as if by magic. It was fascinating to see. There’d be nothing on the wall, then a dark mark would suddenly appear and be gone in an instant. And there were so very many of them emerging one after another that I very quickly lost count.
Those who know such things tell us that each one of these little bats will eat up to 3,000 insects every feeding night. One drawback to rural lighting schemes is that many types of insect find themselves irresistibly drawn to sources of light, where they are easily caught by bats. Every one of these insects has its own environmental niche, within which it fulfils roles not perfectly understood. If we wish to reduce biodiversity we should without fail erect street lighting. Or we could leave the night its own glory.
Moore Hall is made famous by the family of lesser horseshoe bats that have laid claim to the barrel-vaulted cellars beneath the house. The handsome lesser horseshoe population has a measure of importance, if only in that it appears to be dwindling in number elsewhere. The place has other riches just as great. Indeed, Lough Carra, on the shore of which it stands, is an environmental treasure chest, the lid of which is only now beginning to lift.