Bats

•BRITISH NATURAL HISTORY SERIES* QL737 .C5R48 2000 BATS PHIL RICHARDSON Bat roosts Bats were originally caveand tree-dwelling animals but many now find buildings just as suitable for their needs (which is fortunate since there are now far fewer trees available for bats — newly planted conifers contain few hollows and crevices when compared to an old oak). They may also use artificial caves in the form of mines and tunnels. Each bat species has special needs that must be fulfilled at each roosting site, such as the right temperature and humidity. The conditions change at each site throughout a season so the bats require a number of sites which they can visit and so select the best place to roost. All sites need to be well protected from disturbance and basically clean — no cobweb-infested attic would suffice for these very particular mammals. Bats will seek warm sites when they are rearing their naked young and cooler sites when they wish to be inactive and conserve energy such as when the weather is too bad for insects to fly. Bats do not take bedding or nesting material into roost sites but rely entirely on the natural nooks and crannies to give them some shelter. Tree roosts Mature trees can provide a number of suitable roosting places — cracks and splits in willows, woodpecker holes in old oaks and beeches, crevices and holes in the soft, thick bark of Wellingtonias and hollow branches and loose bark on dead trees are amongst just some of the favoured sites. Some bats even roost on the outside of the tree but behind a dense covering of ivy. The position of the tree is important. Daubenton's bats, for instance, use trees that are near, or overhanging, water; other species prefer trees in woodland but tend to use those situated along the edges of woodland or clearings. Parklands, with their well spaced and well matured trees, are also favoured. Finding tree roosts is very difficult. Perhaps the easiest to locate in Britain are the tree roosts of Noctules. This large bat usually uses quite large holes and cracks—an old woodpecker hole in the tree trunk can beideal. On a warm summer's day they may be heard chattering noisily from such holes (trunk calls!) and so can be located even from some distance. Unfortunately they do not always chatter and other species are often much quieter anyway so other methods of location have to be employed. I have spent many a happy day wandering around large tracts of woodlands with a 30-foot (10-metre) ladder, peering deep inside holes in trees in this search for bats (taking steps to find roosts). A small mirror on a stick can aid the search especially in very small holes, and even a microphone on a long pole can be poked just inside a hole and used to eavesdrop on any bat-chat going on inside (ensure that your NCC licence covers you, of course; see Bats and the Law). Often such searches reveal nothing more than a few startled Starlings and maybe a disgruntled owl. Some tree roosts smell quite strongly of bats and have an entrance polished smooth by the passage of tiny bodies. Even when a roost is discovered then it is quite normal for it to be vacated after a few days because the bats use a number of similar sites in an area and like to move around. One bat group, after a great deal of hard work, managed to find a Noctule tree roost, but, on keeping a log of the numbers involved, the group soon twigged that some Noctules were not returning but spending days elsewhere. This led to them finding four tree roosts within half a mile of each other. Noctules rely quite heavily on trees for roosting sites and rare species like Barbastelles and Bechstein's bats also seem to prefer woodland. Pipistrelles, however, commonly roost in buildings but there are always a few t at stay in woodland and roost behind ivy or in crevices. Horseshoe bats are not into trees at all and much prefer something a bit more substantial such as a cave or the roof of a derelict barn or house. A major problem with tree roosts is that they are often lost when the trees are blown over in gales or when they are chopped down (trees with holes are uneconomic in commercially run woodland). The 1987 gales in the south of Britain actually helped Barbastelle bats. Some have now moved into the splits created as the top half of some trees were nearly snapped off by the wind. As if having their homes chopped down wasn't enough, the poor bats have to contend with bird problems too. Starlings like to take over old woodpecker holes and they will not live in harmony with any bats that might already be in residence. Usually the Starling is the victor, and there have been well documented cases where Starlings have evicted Noctules from such holes. In one case a young female Noctule was battered to death by a gang of angry Starlings and her corpse pushed out from the tree hole. (opposite) Noctules. House roosts A large number of bats rely on houses to provide them with shelter. Different species seek different conditions and so the design and construction of a house can influence which bats use it. Bats roost in a number of places (see p. 59) but always require fairly clean, quiet and draught-free positions. It is often necessary to search for the signs of bats (see Bat Droppings) because many tuck themselves deep into crevices out of sight, but a few species do hang in exposed positions. Greater Horseshoe bats, for instance, will hang from attic beams in old houses and barns but require a large entrance hole such as a broken window or open hatchway which eliminates many houses. Long-eared bats are more widespread and also may be seen hanging from ridge beams in an attic. Although many are usually visible, they also sometimes roost between the underboarding or roofing felt and the tiles or slates of the roof and will also be found in the tunnel formed by the ridge tiles and ridge beams. They use this tunnel not only as a secluded roosting place but also as a main route between the inside of an attic and the exit hole, which may be under a ridge tile, under lead flashing around a chimney stack or under the eaves. Short of removing part of the roof, it is very difficult to count the exact number present in an attic but usually this species forms roosts of less than forty bats. Many regularly used sites are in large Victorian houses. Natterer's and Whiskered bats prefer older houses too. They spend less time in exposed positions but are often tucked away behind the underboarding or above the ridge beams. Their exit holes can be anywhere in the roof and often some distance from the roosting place. As dusk approaches they can be heard slowly shuffling along the roof to reach the nearest exit. At one Whiskered Bat roost that I regularly visit they emerge from any of seven holes in the roof and this makes counting them very difficult; so it is necessary to surround the house with bat counters, all watching different exits. The numbers change seasonally but usually there are less than seventy at that site. In the south of England Serotines may be found in houses, sometimes even in modern ones. They need a larger entrance than many other bats and this must limit which houses can be used. Once inside the roof, they move around until they find the most suitable roosting position which may be just under the eaves or perhaps'on the chimney stack in the loft. Other species move their roosting positions in a similar way as the temperature and other factors change during the summer. Most bats roosting in houses form clusters so a group of ten Serotines will not take up much space even though they are large bats. Pipistrelle emerging from gable end roost. The Pipistrelle will, I suppose, always be the most successful houseroosting bat. Being very small, it can squeeze through narrow gaps that deter other species — slots less than Vi inch (10 mm.) wide have been used. In Northamptonshire we find 80% of our Pipistrelle roosts in houses built since 1960. A small gap between the soffit and the house wall (see illustration) gives access into a warm, clean roosting site inside the boxed-in eaves of a roof. If the conditions outside become too hot or too cold then they may move between the roofing felt and tiles, on top of the house wall or into the cavity of the wall. Equally suitable are the bat-sized gaps behind fascia boards or hanging tiles which are often found on modern house walls. A warped plank or slipped tile gives access to these ideal sites. Pipistrelles form much larger roosts than other species at some times of the year and, being small bats, a large number can squeeze into a very small area. I've watched them emerging from the top three rows of hanging tiles above a garage door and, with the help of a team of counters, counted 717 fly out in 40 minutes. Such large roosts are unusual; 200—300 regularly occur but 50—150 is the usual number. They move roosts regularly and also split up into smaller groups so even the smaller roost sites are used for only short periods of time. The roost owner with the 717 bats was more than happy with the final count and we toas e their success in whisky after the last few had emerged. Pipistrelles, like mar > bats, prefer to roost high up, so often choose a gable end wall and roost as close to the top as possible. The habit of Pipistrelles roosting on the outside of the house rather than being inside the attic is well worth pointing out to the roost-owner if he is a little worried about the new lodgers—not that they cause any damage anyway. Whiskered Bat roost in house loft. Large cellars provide good sites for some species. Access must be possible through open windows or through an open outside door and the cellar must be little used by people. Horseshoe bats find such places extremely attractive. Open porches and any covered area next to a house may be used by bats as a temporary roost site during the night. In fact there is a large number of possible places for bats to roost in any house; houses have become of major importance to the bat population. Occasionally, particularly in autumn, bats are found inside the living accommodation of a house. Usually only a single bat has been so brave and it will have entered by accident through an open window — possibly seeking a hibernation site. In some old country mansions bats fly regularly along the corridors acting as if they owned the place. In one such Hall I visited the bats were sneaking in from their roosting site in a stone wall and meandering around the house at tiara-height, occasionally frightening the odd titled lady staying there as a guest. The bats were entering through one of twenty bathrooms up in the servants' quarters. This was rather an exceptional case and usually any bat inside a house is desperately seeking a way out. If a window is left open then they will often find this escape route but if a bat lands on a wall, then carefully cover it in a soft cloth, pick it up and release it gently Access and roostingplaces. outside (preferably after dark). Indoors it is rather difficult to find them if the exact resting place is not pinpointed. At one site I visited the lady of the house had ensured that no one disturbed the bat that she had seen in her living room by sealing up the door with sticky tape. I managed to unstick my way in and searched for 15 minutes in vain. Eventually I found a Pipistrelle tucked into one of the pleats on the curtains which was quite amazing because I had carefully drawn the curtains back and forth a number of times in my search — it must have been getting quite giddy. Bats can get into any room because they can creep under closed doors, but they are frequently found in bathrooms, possibly because the gaps around the water pipes may provide a way in from the attic. Bedrooms are also often visited mainly because many people sleep with the window open. As usual there are always a few extroverts that turn up in the most unusual places. I've come across odd bats under floorboards, in a pan of a toilet (looking rather flushed), in an electric light switch fitting in a house under construction and even in a bath tap which had to be dismantled to remove the bat. House conversion Gable end of a house. If you want to encourage bats to roost in your house, here are some suggestions that will not affect the structure of your house. Roofs: access slots need to be made under the eaves at a gable end and near to the highest point. Also provide an entrance under ridge tiles by chipping out some of the cement and! or by lifting the lead flashing near the chimney. Inside ensure that there is access by providing a gap in the roofing felt near the entry holes. Brush away any dust and cobwebs from the rafters and nail a few panels of fibre board onto the rafters just below the ridge to provide a sheltered area. Outside walls: attach Vz inch (3 cm.) battens to the upper part of a gable end wall (south or west side) and nail on horizontal overlapping boards or hanging tiles, remembering to leave entrance holes to the gap behind. cp Church roosts Bats have long been associated with churches, which certainly provide some excellent roosting places — real sanctuaries for bats. With one in almost every village in Britain, churches play an important role. Although cooler than house roosts, they are quieter for most of the week but do tend to become a bit noisy on Sundays. Many traditional types of church buildings have been added to or repaired over the centuries and this gives rise to a number of suitable crevices for roosting bats. Most are in the church roof with favourite sites being between the chancel and nave, nave and tower, above the altar and in the aisle roof. Bats squeeze between the roof timbers and the church walls, and find plenty of roosting space between underboarding and the lead or tile roof covering. Some bats can even be found roosting behind notice boards and wooden hangings on the walls. Gaining access to these sites inside a church can test a bat s ingenuity. Some enter easily enough under the eaves of the roof or through gaps or holes in the lead flashing on the roof; these may only lead to the roof, not to the church itself, and many a bat lives happily in such a place without setting a wing inside the church at all. Some good roosting places, however, are only accessible from inside the church and so entry may be gained through a broken window or, more commonly, over the church door. These old wooden doors are usually very heavy and sink on their hinges, leaving a bat-sized crack at the top which Pipistrelles, for instance, love to squeeze through. In one church I know a bat regularly squeezed over the top of the closed porch door, flew through the porch, squeezed over the main church door, then flew up inside the church to a roof crevice which it entered with a bit more squeezing, doubtless pretty thin by this time. The porches, especially the roofs, also make good roosting sites. One summer my bat group looked at all 285 church porches in Northamptonshire and found that almost a third were used by bats. Although Pipistrelles were the most regularly found species there were also Natterer's, Long-eared and even Daubentons' bats at some sites. Other species can be found around churches, of course, although some, such as Serotines and Noctules, require bigger crevices and more roosting space. Although belfries have been famed for bats, they are not the best places to find them. If the bells are rung regularly then the disturbance is great for any dozing bat - they don't find the sound of bells ap-pealing! The louvres make the towers draughty places and often birds gain entry which may disturb any bats (see p. 55). Some belfries are quieter, but I rarely find any sign of bats in them. Bats outside often fly close by the tower at night, sometimes circling it and this may have been the reason for its unwarranted fame as a bat r°ostBats have an unfortunate and unexplained habit of flying round and round inside big, open buildings at night; they demonstrate t is ° ten ,rj churches. Little feeding seems to be taking place and the reasons or t ns o behaviour are not clear. It is unfortunate, because it causes an even spreado bat droppings in all corners of the church which can annoy tec eane the vicar. Covering over sensitive areas with cloths a eviates t e; pr ^ Brasses and marble on the floor should be Protected anyway o'thousands of human feet will wear away the surface making ^ .unchurch mouse' insignificant. If small numbers of bats are present then the church mo always gets the blame. „™dirinns are right. The stone Churches can be used in all seasons i e ^ ^ SQ some bats will walls can give conditions very siml,ar Long-eared bats, for ii hibernate there. They are also used at night, Long instance, 63 may often be seen hanging up on the roof beams at night; discarded moth wings, the remnants of a bat feast, will form a small pile below. Bats in churches are often fun. I have been sent some very detailed notes concerning bats that were carefully observed during church services. At one evening service the vicar was commemorating the Battle of Britain and as he spoke of the exploits of the RAF a Pipistrelle repeatedly swooped low over the pulpit causing the vicar to duck; the congregation found it most amusing. In one small village the parishioners are so proud of their Natterer's bats that they suggested fixing a mirror under the roosting place so that the choir could watch the bats during the services. I reminded them that the poor bats would also be able to see in the mirror and might be frightened at the sight of a dozen people grinning up at them. On reflection they dropped the mirror idea. One wonderfully large Natterer's roost in a porch was of national importance so we monitored it regularly. This involved catching a few at dusk with a net across the entrance to see the age and sex of the bats. Everyone had been told of our study, but clerics' memories are sometimes short and the local vicar came breezing up the church path with a hearty wave and 'Good evening, my children' as he walked straight into the net. It took some time to extricate him, the dog collar getting particularly entangled. Brown Long-eared Bat. Cave roosts Bats will use not just caves but any cave-like structures - tunnels, mines, grottoes, ice-houses, cellars, ruined castles, underground fortifications and similar. The temperature of these places is buffered from outside so can remain cold. These are much sought after in winter for hibernation, although bats may use them in summer for night-roosting. Individual bats may use the same crevice deep inside a pitch-black cave system every winter, showing that they have an excellent memory based on the sound picture built up with echo-location. Humidity is vital in winter and needs to be high. The best sites will also give a variety of different low temperatures so different species can all benefit. Subtle changes in temperature or humidity will wake up the bats and can cause them to move - even standing under a bat will cause the temperature to rise enough for arousal. In warmer countries than Britain bats regularly use warm caves for day-roosting, often chosen in preference to buildings. Humans, however, are also attracted to underground sites both in summer and winter, and their unintentional disturbance can drive the bats out so the best sites for bats have to be protected. <2P> The town bat Although bats are often associated with villages, woodlands and the countryside there is many a bat in the town. Plenty of good accommodation and food is to be had if they know where to look. Housing is more diverse than in villages so the choice of roost site is greater for those bats that live in buildings — maybe a centrally heated semi-detached house on the edge of town or a nice warm office block only a few seconds' flight from the town centre. Some bats have even been reported using crevices on tower blocks (flat bats?). Towns don't offer the diversity of insects that the countryside provides, but they have sufficient places where a reasonable number can be found. Many towns, for instance, have rivers running close by, which usually have plenty of insects. The bright city lights are an attraction to insects, which congregate around stadium floodlights, some street lights and airport lamps, and bats soon come along to feed. Town parks provide quite a variety of insect life: some have small lakes and I have found Daubenton's Bat, a species which feeds principally on aquatic insects, on such a pool only a mile from a town centre. Pipistrelles can be found right in the town centre although their main feeding areas may be further afield. Old Victorian factories and associated terraced rows of houses may be home to small numbers of Long-eared bats. One summer I surveyed the town of Northampton at night using a bat detector to locate flying bats and was pleasantly surprised at the numbers in the area, although they were concentrated in a number of large parks, churchyards and along the River Nene. Using a detector in such an area is not easy because it picks up a number of other noises apart from bats — the squeaky wheels of a bicycle, the brakes of a bus or even people walking on gravel. All of these have to be carefully distinguished from bat calls. In one park I picked up a most unusual noise, pointed my spotlight in the direction of the sound and illuminated a courting couple passionately kissing; I had to beat a hasty retreat with angry threats ringing in my ears. Another odd 'chonk' noise I detected was far more bat-like but was coming from under a bush -hardly the place to find a flying bat! Closer investigation proved this to be coming from a grumpy old hedgehog. But it was good to see bats deep inside our concrete jungles; wherever you live in Britain there is always the chance to do some batting. <&>