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Wednesday, 27 February 2008

Time Team vs Bat Team

My favourite TV programme is Channel 4's "Time Team", in which a team of archaeologists dig a historic site and attempt to make sense of it in just 3 days. Although the practical archaeology is interesting, for me the best part is when Stuart Ainsworth and Mick Aston take to the air and attempt to tie their site into the surrounding area. A Roman villa or iron age settlement is all very well, but when you can identify how people travelled to and from it, where they fished or went to market and why they might have chosen that particular place, it all makes so much more sense.

Surprisingly, there are strong parallels with bat work. We tend to concentrate on roosts and hibernation sites. And why not? They are the focus of the bats' activity: where you can conduct a roost census or watch bats swarming. If you have a reason (and licence) to trap and examine them, this is the best place to do it. Roosts are so much more exciting. Roost sites can be hard to find and of course they are where a population of bats may be at its' most vulnerable and in need of protection. Anyone can go for a walk with a bat detector and find a bat in flight, can't they?

Possibly they can, but with a bit of planning and focus, finding bats in flight can help to build up an understanding of how bats use the landscape, in the same way that "Time Team" try to work out how Romans or celts did.

Here's a simple example. Last year I was conducting a series of sunset surveys in some farmland, where a water pipeline was due to pass through. In two places I noted large groups of Soprano Pipistrelles (Pipistrellus pygmaeus) feeding soon after sunset. This can be an indication that a roost may not be far away. An even better indicator is a commuting bat. Bats commuting to and from their roost at dawn and sunset tend fly fast in a straight line: they're on their way somewhere, so why waste energy flitting about, as they might when foraging? A bat flying fast, and straight at dusk, is therefore a good indication that the roost lies in the direction it's coming from. When it's followed by other bats doing the same there is a good chance it isn't far away.

The next survey was in a path running through a strip of woodland. Over twenty Sopranos passed through at sunset, all going in the same direction, the direction of one of the foraging sites I had previously noticed. Soprano Pipistrelles usually roost in buildings and the large-scale map showed a Victorian lodge half a kilometre away, right in line with where they were coming from. I dragooned some help and the next morning we were lying in wait for them near the lodge. But no bats arrived. Spreading the net a little wider, we came across about twenty bats, swarming in the corner of a field. Just to confuse us, there were no buildings close to where they were swarming )they would normally swarm in front of the roost). It turned out they were roosting in a tree, which is quite unusual for Pipistrelles in Scotland. It took another couple of visits to work out which tree the bats they were using: a mature oak.

It's always nice to find a new roost, but the icing on the cake was to also have an understanding of how they were using their habitat. I hope to find time this year to look at some of the other hedgerows and woodland edges which radiate out from the site, and try to work out what other commuting routes are used, adding to the picture of how these bats are using their landscape.

Of course, it'll take more than the three days that "Time Team" get....

The field where we found the Soprano Pipistrelles swarming at dawn. No, the oak tree in the middle isn't the roost: that would be too easy, it's to the left, out of sight.

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Saturday, 23 February 2008

Hibernating Pipistrelles

Today I spent a very pleasant couple of hours wandering through a semi-ruined castle with members of Lothians Bat group. We were there to look for hibernating bats, which occupy crevices and cracks in the decaying stonework. The most popular spot is in the deep, barrel-vaulted ceilings, which in other old buildings are often used for summer or autumn roosting.

To understand why they are so popular with bats, look at the schematic below. In a typical medieval building, arches and ceilings are built from stone blocks arranged into a curve, so that each is supported by the one outside of it. Above this, the infill is usually made of rubble. Over the years the mortar tends to fall out of the gaps between the stone blocks. As long misguided perfectionists don't repoint the stonework, this creates crevices, some of which may extend into spaces within the rubble fill, creating sometimes quite large bat havens. The downside for us is that surveying these buildings quickly causes a sore neck, from peering upwards, pointing a light into the crevices!

What is particularly interesting about the site we visited today is that, not only is it used by hibernating Brown Long-eared Bats (Plecotus auritus), two of which we saw, it is also used by Pipistrelles (Pipistrellus sp.). Remarkably little is known about the hibernating behaviour of Pipistrelle bats: they are rarely found in the mines and caves where larger British bat species are found hibernating. It is generally assumed that they hibernate individually in small crevices in trees or buildings and are probably more tolerant of fluctutations in temperature and humidity. So it was nice to find at least twelve of them here.

Unfortunately, it isn't possible to say whether they were Soprano Pipistrelles (Pipistrellus pygmaeus) or Common Pipistrelles (Pipistrellus pipistrellus): the physical distinctions are difficult enough with a bat in the hand! However, a braver bat-worker than I might note the dark muzzles and wonder if they might be commons.

Click on the picture below to see a larger version of it and you'll see the brown splodge in the centre resolve into a Pipistrelle's face.

The following two pictures show two groups of bats, sharing crevices. I have no idea how many are hiding behind the mortar in the first picture, but the crevice in the second contained seven bats.

My website:

Friday, 22 February 2008

Lime kilns, mines and souterrains

During the recent spell of unseasonably pleasant weather (back to normal now - there's rain going sideways past my window) I and a bat group colleague spent an interesting afternoon in an upland area of Midlothian, looking at various man-made structures with potential to be either hibernacula or summer roosts.

Information on the sites had come from a mixture of word of mouth and references on the CANMORE archeological database (see Armchair roost-searching, February 2008). Some CANMORE references can be little more than a name and grid reference, others include detailed archeological descriptions, which can be fascinating.

The first site was a limestone mine. This is a known hibernaculum, which has been grilled in the past, partly to protect hibernating bats from disturbance and partly to prevent adventurous youngsters from getting themselves into difficulties. I wanted to take a look, as I hadn't previously seen the site and it apparently used to have an underground link with another site, which Lothians Bat Group survey every winter for hibernating bats.

Hibernaculum grilles have quite widely-spaced, horizontal bars, to prevent human access, but make it easy for bat to fly through. It seemed some local wit had been there before us, and left his thoughts for all to see.

The next plan was to look at several lime-kilns, which are prolific in the limestone areas of Midlothian. These are large stone-built structures, usually built into a hillside. Inside is a tall, brick-lined charging-column, into which limestone and fuel was placed. At the base are draw-holes, usually with a barrel-vaulted roof, which are used to control the air-flow, and to draw the completed lime out, ready to be mixed with water and used as fertiliser or building mortar.

Barrel-vaulting can lose it's mortar over time, creating deep crevices, perfect for hibernating bats. Also, the stonework of the kiln can decay, creating roosting opportunities. Unfortunately, none of the three kilns looked at had many crevices in the draw-holes, but all had decaying stone-work to a greater or lesser extent.

One of the kilns was a massive structure, with two charging columns and six draw-holes, all in excellent condition, making me wonder if it may have been rebuilt in the 1930s, when the government offered incentives to farmers to burn lime, due to concerns about deteriorating land fertility.

At the other end of the scale was a badly-decayed kiln within dense woodland. Landslips had partially buried it and we found a solitary bat dropping in a huge crack in the stonework. A single dropping doesn't make a roost, but it may be worth a return visit in the summer.

The third site had a lovely Barn owl (Tyto alba) roost: a deep hole, high up on the side of the kiln, with long white streaks, left by the owl's characteristic runny droppings. Inside and on the ground below were plenty of large, dark-coloured owl pellets.

There was no sign of the owl (or owls), though it could have been deep inside it's roost-hole, out of sight. Not a bat roost, but it was very nice to see signs of this scarce bird, all the same.

Having seen enough lime kilns to last a while, the last site of the day was a soutterain. These are iron age (about 700BC-500AD) structures, believed to be underground storage facilities. In an age before refridgeration, building a shallow, stone-lined tunnel was a good way to keep food dry and cool, to last through the winter months.

This particular soutterain lies in a small, fenced-off area in the centre of a field. Accessed via a low roofed doorway (and when I say low, I'm talking about crawling on hands and knees), and short entrance tunnel, it is almost 16 metres long and up to 2m wide and high. The walls are made of unmortared stone, full of very deep crevices.

No hibernating bats were visible, but there could have been legions of them, out of sight! With a low, stable temperature and high humidity (yes, it's mud you have to crawl through...), the conditions are ideal for a hibernaculum, especially as it is in area full of excellent bat habitat.

The soutterain is out of sight of the nearest road and probably not known to many people, so is unlikely to suffer much disturbance, especially in winter. That said, a team of Powergen workers, dangling from nearby power lines looked fascinated by what we were up to.

More information about barn owls:

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Sunday, 17 February 2008

Confessions of a bat surveyor

I sometimes find working with bats a little humbling. Not only is there a vast amount we don't understand about the bats here in the UK, let alone worldwide; there are many big bear-traps, waiting to catch the unwary bat surveyor. I thought I knew most of the worst ones, but today I discovered I had fallen into a trap I actually knew about, a really obvious one. Oh bum!

I think Brown Long-eared Bats (Plecotus auritus) must be my favourite bat species (hence my choice of web address). They are very attractive (by bat standards), with enormous rabbit-ears, dwarfing their bodies and a face that makes them look faintly bemused by life. Better still, they occupy a very specialised and fascinating niche: emerging late, flying slow and using their ears to listen for their prey. Not called the "whispering bat" for nothing, their echolocation is very faint, allowing them to catch those moth species which have developed rudimentary ears to help them take avoiding action when an echolocating bat is near. In short, they are nothing short of amazing.

Brown Long-eareds are generally easy to identify in Scotland: nothing else has ears anything like that size. In the South of England, things are harder as there is another long-eared bat: the Grey Long-eared Bat (Plecotus austriacus), which is extremely difficult to separate from it's brown cousin. Bat-workers there have to resort to measuring tiny parts of the bat's body to separate the two. Unfortunately, I don't have that excuse!

The trap I fell into was to identify a Brown Long-eared Bat as a Daubenton's Bat (Myotis daubentonii). How is this possible? The Daubie has tiny ears by comparison! Long-eared bats have an endearing habit of folding their ears under their wings when they go into torpor, to help them retain warmth. This leaves the tragus (the spear-like middle-part of the ear) sticking up, looking for all the world like a small ear...

In my defence, I must say that I wasn't alone, there were several (nameless) people with me on a hibernaculum survey last month, and they share in my crime! I even took a photograph of the bat in question, which, when enlarged, clearly shows the roots of the ears folded over the flanks, but it was a bit fuzzy, so I didn't look closely at it until this evening. Today we did a second survey of the hibernaculum (the National Bat Monitoring Programme requires two winter surveys, a month apart). We found a bat in a similar place, in the same attitude, yet seeming to be a different species. It seemed too much of a coincidence, so on arriving home, I checked the photographs. It's a fundamental error, but I suppose we were peering in torchlight at a bat on the roof of a mine...

Anyway, in the spirit of public humilition and restitition I hereby present my guide to not making the same mistake! The three pictures below tell the story.

Firstly, the Brown Long-eared in question. Note the wing roots folded over the flanks, the shape of the tragi (masquerading as ears) and their pale colour. If the picture looks a bit odd, it's because the camera is pointing up and zooming into a bat hanging from the roof of the mine.

Next, a Daubenton's Bat for comparison.

Finally, it's close relative and another species commonly found in our hibernacula: the Natterer's Bat (Myotis nattereri)

Now go forth and learn from my error! Mea culpa, mea culpa, mea maxima culpa.

Please remember that handling bats, disturbing them or their roosts, photographing them or surveying their hibernacula, all requires a licence. If you're interested in getting involved, join your local bat group. See here for a list of contacts:

For information on the National Bat Monitoring Programme (NBMP) see:

My website:

Saturday, 16 February 2008

The kitchen table harp trap

For some time I'e been thinking about building a harp trap for my own use and I'm delighted to say that this winter I have finally found the time to do so. What is a harp trap? Also called a Tuttle trap (after Merlin Tuttle, whose invention it is), it's an ingenious trap which catches bats in flight, without harming them.

It works like this: a bat flies towards the trap and recognises a harp-like collection of vertical nylon lines about 2.5cm apart. With great agility it successfully flies between the lines, but what it doesn't expect is a second set of lines offset from the first, so that it can't avoid hitting them. It then slides unharmed down the lines, into a canvas bag below. The bat will try to climb the side of the bag, so it can take off again, but the sides of the bag are lined with thick, slippery polythene. The bat can climb the canvas, but soon reaches the seam where it is joined to the polythene and can go no further until it's removed.

Harp traps can be marvellously effective, when used properly. They are particularly good at trapping bats leaving roosts, as the bats have less time to see and avoid the trap than they would if they were free flying. More importantly, the bats are entirely unharmed and in my view suffer less stress than if caught in a mist-net. The problem is the cost: a single harp trap costs upwards of £800. See for pictures of a commercial trap made by Austbat.

I reckoned that I could reduce that cost to under£200 by building my own trap, and add a few ideas of my own. Firstly, I wanted a smaller trap. With a catching area 1.8m wide and 2.4m high, the Austbat trap is unwieldy in some circumstances. It is also difficult to erect, as it is necessary to unroll and stretch the lines every time the trap is used. This process is fraught with difficulty at the best of times, let alone in darkness and pouring rain, when you're tired and fed up at 2am! My thinking was that a smaller catching area could allow for the harp section to be permanently erected within a frame. When not in use, the frame could be bagged , with the legs and catching bag removable for transport. A smaller trap would also be lighter and could be lifted on a couple of poles to cover the entrance to a high tree roost or the eaves of a roof. You can do that with an Austbat trap, but you need ropes and a team of stout people singing sea shanties, to haul it up!

And here it is...

The catching section is slightly over 1m square, with the frame, legs etc, made from lightweight square-section aluminium, which also has the advantage of being an easy material to work. The legs are easy to remove, without affecting the rest of the structure, so that the frame can be slung between two poles and lifted up to a roost entrance.

I took the opportunity to address two weaknesses I've noticed with the Austbat and similar traps. They have the nylon monofilament tied around the frame top and bottom. This has the effect of making the nylon vulnerable to scraping against rough surfaces and fraying or breaking. I tried to address this by tying the nylon lines to tiny hooks screwed into the frame, so that the frame itself protects the nyon.

The Austbat traps are also vulnerable to escapes at each end of the bag, as the plastic material is only attached to the two long sides. I have made a point of attaching plastic to the two short sides, in the hope of preventing that. The base of the harp frame sits slightly inside the bag, to allow this to be possible.

The hardest part of building the trap was sewing the canvas and plastic. Dressmaking isn't a skill of mine anyway, and it takes a lot of effort to push a sailmakers needle through several layers of the thick canvas. My fingers may never be the same again!

Where does the kitchen table come in? That's where I built it (it's too damn cold in the garage at this time of year!) The table still bears the scars.

Of course, I'm rather proud of the trap, but success isn't realy measured by appearance, or sound engineering or even my pride - it's measured by whether it actually works: will it catch bats?

Watch this space...

Please note that the use of a harp trap to catch bats in the UK is heavily restricted. I am able to use one because I have a roost visitor's licence, endorsed for the use of a harp trap, I am also licenced to catch a number of bats for a specific scientific study. Trapping bats without he necessary skills and licence is illegal and likely to be harmful to the bats. If you're interested in getting involved in this kind of work, the best starting point is to join your local bat group.

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Thursday, 14 February 2008

Armchair roost-searching

The holy grail of bat-work is finding roosts. Finding and watching feeding or commuting bats is great but the roost sites are the centre of the network of bat activity. More importantly, if we know where roosts are, we can ensure they are safe from disturbance or destruction.

So how do we find new roost sites? Basically, it involves one of three methods, though all three require a great deal of luck!

Method 1 is to seek out commuting bats and attempt to let them lead you to the roost. Great fun, and sometimes very successful, although hard work.

Method 2 is to simply stumble across one. Bat calls from worried householders can bring new roosts to light. Many bat-workers have had someone say casually "Bats? Oh there are hundreds of them in our attic - you should come and see them." A remarkable number of people have bats in their homes, are perfectly happy and don't make any fuss about it.

Method 3 is to carry out a dawn survey: bats tend to swarm around the entrance to their roost for 20-30 minutes just before dawn, so looking for them can be quite effective.

Whichever approach (or approaches) is used, some homework helps provide the best return for time and effort, and this is the ideal time of year to do it. We're lucky to live in an internet age and the web is stuffed with handy resources.

The NBN (National Biodiversity Network) Gateway houses a lot of records of roosting bats in Scotland, though it seems patchier south of the border. Go to, type a species name into the search box and then select the interactive distribution map. This is a handy (though slow) gadget which allows you to navigate your way around the records held. Unless you make special arrangements with data providers, you can only view the records at an accuracy of 100m, but that's a starting point for a roost search. Don't assume a record means that a site is known about. I recently found six local records of Brown Long-eared Bat roosts, which weren't know about in our local bat group. Remember also that an absence of records may mean a shortage of bat-workers, rather than a shortage of bats!

Maps are, of course essential for this sort of work. The Ordnance Survey have made their mapping available on-line, as an interactive tool. In my view nothing can ever replace a dog-eared 1:25 000 scale map, complete with coffee-stains and ten years-worth of pencil marks and scribbles, but I have to admit that the Get-a-map service is extremely convenient!

Some bat roosts are found in historical man-made structures: old buildings, bridges, mines, lime kilns etc. The Royal Commission on Ancient and Historical Monuments Scotland (quite a mouthful!) have an on-line database of archaeological site records called CANMORE, which can be searched either manually or via an interactive map. This is similar to the NBN Gateway, but faster. It's a terrific resource, which I've been using recently to search for potential hibernaculum sites, such as world war 2 pill-boxes, disused mineworkings etc. Go to and try a CANMORE search. Even if you don't find a potential roost, you'll be amazed what archeologists have found near where you live!

Once we have a site which may be of interest, what can be done next? Taking a close-up look from the air may help. Windows Live Search offers an interactive satellite photograph service, similar to the well-known Google Earth, but with significantly better coverage. Go to and try zooming in to the site of interest. If your site is in a high definition area, not only can you zoom in close and see what it looks like, you can also get a sense of the surroundings habitats, flyways, foraging potential and so on. It's also a damn good toy just to play with! (I know the photographs of York were taken on a Tuesday because my Mum has her washing on the line!)

Knowing my luck, summer will come along and I'll be too busy to follow up these sites, but at least I will have had a winter bat "fix" and being familiar with these resources often comes in handy with all sorts of fieldwork planning.

My website

Tuesday, 12 February 2008

I want to live in Poland!

I had the privilege today of hearing a fascinating presentation by John Haddow of Central Scotland Bat Group about the Nietoperek Bat Reserve in Poland.

Nietoperek is something of a legend in the bat world: a massive underground system of world war 2 fortifications: with 32 kilometres of tunnels, an amazing thing in itself. But what really adds the thrill is the fact that they are used as a hibernation site by mind-boggling numbers of bats.

For several years John has been taking part in the annual census of hibernating bats, when a large group of skilled bat-workers from across Europe come together to count the bats in the tunnel system. The numbers are incredible: over 30,000 bats were present this year. The predominant species are Greater Mouse-eared Bats (Myotis myotis), with many other species represented, including Daubenton's Bat (Myotis daubentonii), Natterer's Bat (Myotis nattereri), Brown Long-eared Bats (Plecotus auritus) and Barbastelles (Barbastella barbastellus).

Why do they gather in such huge numbers and (more importantly for us!) why don't they do so over here? The numbers of bats we see in Scottish hibernacula are tiny by comparison! According to Frank Greenaway, it's all a matter of our Atlantic climate versus the continental climate of Poland. Put simply, it gets a lot colder in winter in Poland and stays that way for longer, so bats have a greater imperative to find an underground site with a stable temperature.

I also came across a wonderful new word: Chiropterology: The visitor centre near Nietoperek is called The Chiropterological Information Centre. I now know what to say when people who know nothing of ecology ask what I do for a living: I'm a chiropterologist!

The Chiropterological Information Centre:

Frank Greenaway's video on bat torpor:

This site describes a visit to Nietoperek:

My website:

Sunday, 10 February 2008

Life in a hostile habitat: the wing of a bat

For several years I have been taking a close interest in bat parasites. Indeed, as I write this, to the side of my laptop are a stack of specimen storage vials containing over 400 parasite specimens, taken from over 80 individual bats.

Many of my bat-worker colleagues find this interest hard to understand. Admittedly, they do not fall into the charismatic megafauna "cute and cuddly" bracket, but many are impressive animals in their own right.

Spinturnicidae are the largest and most obvious of the mite families, which use bats as their hosts. Superficially like miniature claw-less crabs, they live out their entire lives on the wing and tail membranes of their host, never leaving the bat, except to pass to a new host. Unlike many ectoparasites, they do not take refuge in the bat’s fur.

The wing membrane is a mind-bogglingly hostile habitat: in flight the wings flap 10-15 times per second, requiring immense grip and an aerodynamic profile to stay attached. Like all mammals, bats regularly groom themselves, and unable to hide in the bat's fur, these mites need to make it difficult for the bat to dislodge them from the wing. Vulnerable eggs or larvae would not survive long.

To survive in this difficult habitat Spinturnix mites have several adaptations:
  • Their short, stout legs are extremely strong.

  • Feet are equipped with large claws and sticky-hooked pads, to cling on.

  • The body is flattened and armoured with chitinous plates.

  • Egg & larval stages are completed within the female's body.

  • The female gives birth to a single protonymph,

Removing Spinturnix specimens from the bats is an uphill struggle. As soon as the mite realises it is threatened it either runs across the wing membrane (and they're fast), or it hunkers down and grips the membrane tightly. Either way, the best way to remove them without risk of harming the bat is to dab it with a drop of ethyl acetate or 70% alchohol, which usually dampens it's ardour.

Having gone through the difficult processes of catching a bat, then removing the mite, the fun is only beginning! Attempting to identify of bat mites has led me to seek documents published by the Zoological Society of London in 1923, by the University of California in 1960, and most recently a Russian-language parasitology journal! But it's all good, clean fun....
Top - Daubenton's Bat Myotis daubentonii, showing the wing membrane.
Middle - Close up of the wing membrane, with a Spinturnix myoti mite.
Bottom - Adult female Spinturnix myoti.

Anyone wanting to study bat parasites in the UK is lucky to be able to draw on the work of Anne Baker of the Natural History Museum. With Jenny Craven of Leeds University she produced a checklist of species in 2003, which is available on the web:

Please note, trapping, handling or otherwise disturbing bats in the UK is illegal without a licence from one of the statutory nature conservation organisations (SNH, CCW, Natural England).

My website:

Wednesday, 6 February 2008

Two roosts for the price of one

Many commercial building surveys for bats result in a big fat nothing (often they are requested simply to confirm the absence of bat roosts prior to demolition or renovation), so it was nice recently to find one building with two separate roosts.

Obviously, I can't say on here where the site is, but with great riparain and woodland habitats at hand, plus several large attic spaces, it was a promising site. The first attic space I entered revealed many accumulations of bat droppings, mostly running in a line below the ridge. This was because the bats had been roosting in the space between the fibreboard lining and the roof tiles. Droppings had fallen into the attic through gaps in the fibreboard and these gaps were particularly prevalent at the ridge. Given the small size of the droppings, the large quantitiesof them and the fact that the bats clearly have an affinity for crevices, makes it likely that they are one of the Pipistrelle species, but I can't be certain of that until they return to the roost later in the year. (An advantage of being in Scotland, with a limited range of bat species: I would be far less willing to make even tentative suggestions as to species if I were in the south-east, where there are more than twice as many species!)

Incidentally, you can tell bat droppings from mouse droppings because, although they are a similar tiny size and cylindrical shape, bat droppings tend to be much darker and have a "knobbly" texture because they are largely made up of pieces of hard chitin from insect ectoskeletons. If you rub a bat dropping between your fingers it will usually turn into a gritty dust, whereas the mouse dropping will probably squash between your fingers (yum!). In the pictures you can see how some of the older droppings are turning grey.

The second roost was in a separate attic space. The droppings there, instead of being concentrated in piles, were scattered everywhere. They were also a little larger than the others and had a slightly shiny appearance. It's possible these were left by Brown Long-eared Bats (Plecotus auritus), which tend to roost in the apex of an open attic space and fly around to warm up before emerging from the roost. Later I analysed some of these droppings under the microscope and the shiny appearance was caused by large quantities of moth scales. (Excuse the picture quality below - photomicroscopy isn't my strong point!) Moths form a significant part of BLE food, especially in Scotland, but again, I won't know what species they are for certain until they return later in the year.

If you fancy trying bat dropping analysis (it really isn't as horrid as it sounds) try to get hold of a copy of "Identification of Arthropod Fragments in Bat Droppings" by Caroline Shiel et al, published in 1997 by the Mammal Society. (Try Pennine Books

Tuesday, 5 February 2008

What's in a bat box?

Well, hopefully...bats.

When the first bat-box schemes were launched, in the 1970s, using sponsorship from viewers of BBC TV's "Nationwide" programme, there was one design: the standard wooden bat-box. They're not unlike a blue-tit nest-box, but instead of a hole on the front, the bats access by climbing a roughened board and entering through a narrow slit at the base. Easy and cheap to make from a single plank of rough timber, there must be many thousands of them around the country and they're as effective as ever.

Bat boxes do a great job of supporting bat conservation by raising awareness, providing an easy way of monitoring local bat populations, and by providing bats with roosting opportunities in places where alternatives are limited. Annual bat box occupancy checks carried out by local Bat Groups also give a great opportunity for novice bat-workers to see bats close up (strictly supervised by someone with an appropriate licence).

Today, many designs are available, to the extent that choosing bat-boxes is almost as hard as choosing a new car! Do we want it to emulate narrow crevices, to suit Pipistrelles, or bigger tree-holes, to suit Noctules? Do we want cheap and cheerful wooden construction, or shall we push out the boat and use deluxe woodcrete bat-boxes? How about a wedge shape? Should the door be on the top or at the front? Should it be painted black? And so on...

Here in the Lothians, a bat box containing anything other than Pipistrelles is sadly a rarity, though a box full of Pips is still a welcome sight. Whilst the traditional boxes are well-used, they seem to prefer slimmer, more crevice-like designs. However, the most popular design seems to be the dome-shaped woodcrete (a cement and sawdust mix) boxes, made by Schwegler. They're not cheap, but the occupancy rates are definitely higher.

Anyone thinking of putting up bat boxes would be well-advised to take advice from their local Bat Group. A little experience and foresight in choosing the right boxes and positioning them correctly will make a big difference to their success...or otherwise.

The great hibernaculum search

Ever since we had to cease surveying one of our bat hibernaculum sites because of dangerous subsidence, Lothians Bat group members have been keeping an eye out for other hibernation sites to survey, to add to our two remaining ones.

We have revisited an old limestone mine, last surveyed in the late 1980's, with some success. The January survey there revealed one Natterer's, three Daubenton's, plus an unidentifiable bat's bum poking out of a crevice close to the entrance. It doesn't sound like much, but five bats is a fair result for almost three hours spent underground! (The bat pictured here is a Daubenton's Bat Myotis daubentonii)

Here in Scotland, most hibernating bats are found in old mines or caves, and they tend to be tucked into crevices and holes. For this reason, surveying for them is a slow and laborious business and it's likely that we only see a tiny proportion of the bats present. Nonetheless, it's important work, as we can compare results year-on-year and our findings are fed into the National Bat Monitoring Programme (NBMP).

I have never made any bones about the lack of joy that hibernaculum surveys bring me! The sites we currently visit are fairly civilised, with high roofs and not too much water or clay to wade through, but that's just the luck of the draw! Lulled into a false sense of security I recently agreed to take a small group of intrepid (more so than me) bat-workers to search for a couple of almost-forgotten mines, to see if they could be added to the Bat Group's survey programme.

The first site looked ok at first, though a low roof meant stooping (being 6 feet tall doesn't help!) Most of the floor was covered with about 12 inches of water and one by one we each experienced the joy of rapidly and unexpectedly descending twelve inches as the fine limestone silt undert he water acted like quicksand. Deciding that discretion was a good idea, we retreated and were lucky to leave the site with the same number of wellies we entered with!

The second site was even more entertaining, as recent heavy rain and a build-up of rubbish at the entrance meant that the water was within eighteen inches of the roof. I wasn't too keen on the colour of the water, either.

If you're interested in hibernaculum visits please ensure you work with your local bat group. Not only is it potentially dangerous to do this without appropriate equipment and experience, it requires a bat roost visitor's licence with a specific endorsement. Accidentally disturbing bats during hibernation is very easily done and can have a devastating effect on the bats.

National bat Monitoring Programme:

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