ON a mild evening, take a wander down a quiet country lane or seek out a languid pool in a nearby river. As the soft shades of dusk fade into night, there is every chance of spotting a bat flickering over a hedgerow or just above the surface of a river or loch. One minute it is there, the next it has gone. But then it is back again, dipping and diving, spiralling and swerving.
The chances are it will be a pipistrelle, our smallest bat, only two inches long and weighing in at a quarter of an ounce. Where there are moths and other flying insects, then there are bats and some of the best places to watch them are along the woo
ded margins of slow-flowing rivers and lochs. They are also common in woods and open ground where there are plenty of bushes. The damp oakwoods of western Scotland are particularly good places for bats, which are attracted by the vast swarms of midges and other insects there. But bats can be pretty adaptable, and I have seen pipistrelles at 1,600ft in Glen Geusachan in the Cairngorms, where the nearest trees are at least a couple of miles away. Even here, on a warm summer's evening there are plenty of airborne insects over the heather, with the bats using nearby rock fissures to roost during the day.
Scotland's cool climate means the country is not well represented in bats. Of the 17 resident species in Britain, only four are fairly common in Scotland, with a further three having a more sporadic distribution. The commonest is the pipistrelle, once thought to be one species, but in recent years recognised as two – the soprano and the common pipistrelle – the frequency of the echo-location call, which they use to "see" and detect flying insects, being the principal distinguishing feature.
A good way of seeing for oneself the effectiveness of this echo-location is to flick a small pebble into the air in front of a flying bat, which will cause it to quickly deviate to investigate the airborne projectile. Fly fishermen are all too aware of the perils of accidentally catching a bat during casting.
Our most attractive bat is the long-eared, its big ears well adapted for hunting. For bats, larger moths make a nutritious meal, but when a moth detects the high-frequency call of an approaching bat it is often able to take avoiding action – sometimes by closing its wings and dropping quickly earthwards. Not to be outdone, the long-eared bat has developed an extremely weak echo-location call, so soft that it is sometimes dubbed the "whispering bat". This means it is able to approach flying moths without being detected quite so easily, its large ears a useful aid in countering its soft echo-location. The broad wings of this species also enable it to hover near vegetation and pick off insects crawling among the leaves.
Both pipistrelles and long-eareds frequently use houses as their maternity roost sites. Long-eareds often roost in the attics of older houses, where they form small clusters in the roof timbers, whereas pipistrelles are more often found in houses less than 40 years old and prefer to roost in confined spaces such as hollow walls or underneath roof slates.
The other bat most likely to be encountered in Scotland is the Daubenton's bat. Emerging well after sunset, it is closely associated with water, and can often be seen skimming low over the surface of rivers and lochs feeding on insects. Sometimes it even uses a specialised hunting technique which involves picking insects off the water surface by using its large feet as grappling irons.
For a number of reasons, including habitat loss and a lack of suitable roosting sites, the bat population has declined considerably in the last century and because of their vulnerability they have been afforded special protection, which makes it illegal to disturb bats and requires householders with bats on their property to seek advice from Scottish Natural Heritage before carrying out any remedial treatment or building work.
Even simple works such as replacing fascia boards or a slipped slate can block access to a bat roost or cause them to die by being trapped inside. If you do have bats in the roof of your house, then count yourself lucky. Bats often invoke horror among people, more through ignorance and wild imagination than for any real reason. They are fascinating and attractive creatures which play a vital role in our ecosystem. Or to put it another way, bats need friends.
