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Tuesday, 25 March 2008

The Great Hibernaculum Hunt Revisited

A couple of times recently I've described the hibernaculum survey work I've been doing, together with several other members of Lothians Bat Group. We've been looking at potential hibernacula and sites with historical winter records of bats, in the hope of adding to our list of active hibernation sites.

The goal of all this work is to ensure that hibernacula - the most vulnerable of all bat roosts - are protected and also to to contribute as much data as possible each year to the National Bat Monitoring Programme.

(Carol Ann demonstrates how some sites are just plain awkward to access)

Having reached a stage when I've arrived at the bottom of my list of possible sites, when we're running out of winter and when frankly I've seen enough wet, muddy and claustrophobic underground places to last a lifetime, I thought it would be interesting to take stock.

Including surveys of exisiting hibernacula, both in the Lothians and in Dumfries and Galloway, in the past three months I have surveyed:
  • 6 limestone mines
  • 1 copper mine
  • 7 lime kilns (one of them flooded to about half an inch higher than my waders!)
  • 2 tunnels
  • 4 castles
  • 2 soutterains
  • 1 WW2 underground bunker
  • 2 pill-boxes
  • 3 air-raid shelters

Out of all those sites, the following records were made:

  • 16 Natterer's Bats (Myotis nattereri)
  • 5 Daubenton's Bats (Myotis daubentonii)
  • 1 Unidentified myotis bat (Myotis sp.)
  • 6 Brown Long-eared Bats (Plecotus auritus)
  • 16 Pipistrelles (Pipistrellus sp.)

(Two Natterer's Bats hibernating in a cave roof crevice )

The frustration is that all the bats were in the sites where we expected to find them. In other words: no, we haven't found any new hibernacula! That said, there are several sites which have strong potential and will be revisited next year. The disappointing result is probably only to be expected. Bats are extremely discerning about sites they use for hibernation: their requirements regarding temperature, humidity, constancy of both and lack of disturbance are very precise. That is exactly why it is so important to find and protect these sites.

(A Daubenton's Bat hibernating in a gap within the wall of an underground stone bothy)

So, after many days of clambering about in thick gooey mud, with chilly water running down my neck, was it all worth it? Well, yes it was. Nigel, Carol Ann, Rachel, Stuart, David, Natalie, Freda, Max, Peter and all the other bat group members I've surveyed with are great company and there's a real feeling of doing something valuable for conservation, even if it's only to strike a site off the list.

Those sites in which we didn't find any bats often produced other compensations. Amongst other things, I've seen four different Barn Owl (Tyto alba) roosts, more Roe Deer (Capreolus capreolus) than you can shake a stick at and some rather attractive grey slugs with a cream stripe (species, anyone?). Plus, loads of fascinating human history: from 3,000 year-old soutterains, through 600 year old castles to World War II bunkers and pill-boxes.

Oh, and I've got through enough Persil to sink a ship....

(Nigel, looking intrepid in a copper mine)

Please remember that hibernating bats are extremely vulnerable to disturbance. Carrying out hibernaculum surveys requires a roost visitor's licence with a specific endorsement. Entering a hibernaculum and disturbing hibernating bats is a criminal offence. Many hibernation sites are also extremely dangerous. If you are interested in doing this type of survey work contact your local bat group, who can help you to get involved legally and without risk of harming the bats or you.

More information on the NBMP:

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Friday, 21 March 2008

Hark the Herald...Moth

Visits to bat hibernacula sometimes produce sightings of other species, which also choose to hibernate in caves and mines. Mosquitoes and bees are occasionally found, but the ever-present companion of the hibernating bat is the Herald Moth (Scoliopteryx libatrix). I don't think I can remember every going into a hibernaculum without also finding Herald Moths: sometimes many dozens, often just one or two.

According to Butterfly Conservation, the organisation charged with conserving our diverse butterflies and moths, there are over 2,500 species of moth in the UK. So why the Herald should be the only one that seems to choose to overwinter in cavses and mines isn't clear. Many species spend the winters as eggs or as pupae, but quite a number apparently do overwinter as adults.

The Herald is a rather attractive animal, with wavy-edged wings coloured with reds and browns, which help it to blend in with dead leaves and avoid predators.

An interesting coincidence is that the Herald is a member of the Noctuidae family of night-flying moths. Something which sets them apart from other moth families is that they have developed a rudimentary hearing organ, which is used to detect the echolocation calls of approaching bats. On hearing an approaching bat the moths wings go into spasm, causing erratic flight, so that the moth is able to evade the bat.

The bats have the last laugh however, in the form of the Long-eared Bats (Plecotus spp.). which have evolved to get by with a very faint echolocation call. Their slow flying speed means that they have less need than other species for advanced warning of obstacles and their phenomenal hearing allows them to listen for prey. Their very faint call (they are known as the Whispering Bat) means that moths aren't able to hear them coming. Thus, a commonly-found sign of Brown Long-eared activity is a pile of discarded moth wings.

It is quite usual to see hibernating bats covered with droplets of condensation. What sparked off this foray into lepidoptery was the discovery today of a Herald in the same state, with huge droplets of water on it's antennae, creating the impression of some kind of miniature bog-eyed monster. Maybe this is the first sign of the moths evolving some form of revenge on the Long-eareds...

For more information on Butterfly Conservation go to

Another good source of information on moths:

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Wednesday, 12 March 2008

Bats, bombers and acoustic mirrors

One reason why I first started working with bats was that bat work combines my love of wildlife with my longstanding interest in electronics. Fortunately people who do surveys with me tend to tolerate my tendency to come up with strange new ideas or pieces of equipment!

Several years ago I found myself wondering whether parabolic dishes might have a place in bat work. These are used in the recording of bird calls and other wildlife sounds and look similar to TV satellite dishes. In essence, the dish reflects sounds into a focal point, where a microphone is placed. This has two effects:
1. Sounds are concentrated by the dish, making them louder.
2. Sounds are picked up from a narrow direction, filtering out background sounds from either side.

Incidentally, not just any dish will work: a parabola is a specific curve, calculated using a mathematical formula.
I experimented with an old Sky TV dish and found that when I put a bat detector at the focal point of the dish, bat calls became louder and so could be heard from further away. However, it was clear that this would have limited practical uses, as it only worked when the dish was pointed directly at a distant bat. People recording bird calls can see a bird and point a dish at it. Bats don't allow that luxury!

More recently I became aware of something called a parabolic plane. This is sometimes used in microwave radio applications. It is like a dish, but only curved in one plane, a bit like Rolf Harris's wobble board. Between the wars gigantic parabolic planes up to 200 feet long by 26 feet high were built at strategic sites around Britain's coast. These "acoustic mirrors" were used to listen for approaching bombers: operators could hear an aircraft from 20 miles away. Unfortunately they were never used for their intended purpose: by the time World War II broke out, radar had taken over.

Image (c) English Heritage

The beauty of a parabolic plane is that it only concentrates sound from the horizontal plane, so that a bat flying in front of one at any height should be heard. It could be possible to create a kind of listening curtain: in theory any bat passing through it would be detected. To test this I made up a prototype reflector, using foam board, card and sticky-backed plastic (eat your heart out, Blue Peter) and tried it, using a low-level ultrasound source as an artificial bat.

The prototype is only 60cm by 20cm, so I wasn't expecting miracles, but tests at varying ultrasound levels showed that, using the reflector a Duet bat detector could pick up the artificial bat between 30% and 70% further away than it could on it's own. Positioning of the detector microphone is critical, as it needs to be at the precise focal point of the reflector for best results. The half-brick will need to be replaced by something with a bit more finesse!

There is some interesting potential for parabolic planes, but there are some potential draw-backs too. In theory, the bigger the reflector, the further away you can hear bats. But a bigger reflector also means the bat would be audible for a shorter time, passing through a narrower curtain. (The acoustic mirrors could hear aircraft from 20 miles away and place them to within 1.5 degrees.) Ideally a bat needs to be audible for 1-2 seconds, to be sure enough of it's call is
recorded, to allow for identification, so this may limit possible size..

Another problem is the practicality of lugging a big reflector around. Even using it in a fixed position, more than 2-3 metres in width would probably be impractical, unless as a permanent fixture. Any fixed-location survey involves predicting where the bats will fly, and they don't alway read the same books as us!

More about acoustic mirrors:

My website:

Tuesday, 11 March 2008

Right-diddly-wotsit squirelly

If John Donne had been an ecologist, rather than a form of suffering for High School English students, he might have said "No bat is an island". That's an appalling piece of paraphrasing and as I write it I find myself glancing over my shoulder, in fear of an avenging teacher. However, my point is this: as bat ecologists it is very easy to become entirely focussed on "our" species and lose sight of their place within the ecosystem.

With that in mind (and because the bats are far from active at present) I present a small diversion from the world of bats, into the world of bryology: the study of mosses and liverworts. Where's the relevance? Woodland is probably the most important habitat for bats and a key part of woodland structure are the mosses and liverworts. In some British woodlands they outweigh vascular plants in terms of biomass and they form an important habitat for many invertebrates which may ultimately become bat-food. Also, I like them and it's my blog.

With over 1,100 species of bryophyte in Britain, some hard to identify, there are limits to what a casual naturalist can achieve, but to show that this is no excuse, here's my guide to five common woodland mosses everyone should be able to identify, even without a hand-lens. Just to prove my point, they were all photographed in my local (rather poor) woodland this afternoon, whilst walking the dogs.

Rhytidiadelphus squarrosus (Right-id-aye-ah-dell-fuss squaw-row-suss)

If you're a keen gardener you probably know this moss already. It's common name is Lawn Moss, for good reasons. In woods and lawns it often forms dense carpets and is very easy to identify: pull up a bit and you'll see it has a bright red stem and green leaves, which are squarrose: they emerge from the stem and bend downwards.

Thuidium tamariscinum (thoo-id-ee-um tam-ah-riss-eye-num)
My personal favourite, this plant is very easy to identify. It is regularly tripinnate, meaning that the stem is symmetrical, with each branch off the stem divided into sub-branches, which are themselves further branched. In other words, it looks like a miniature fern. The stems are always green or black (if red, you've got Hylocomium splendens) and quite springy, so the little fern-like stems often arch over, like a bramble. It's common name is Tamarisk Moss.

Dicranum scoparium (die-crane-um scop-ah-re-um)
This is an upright moss, often forming dense tufts. The giveaways are the long, thin, pointed leaves, often densely packed together and turning to one side. It's common name is Fork Moss.

Sclerapodium purum (scleh-rah-podium poo-rum)
The leaves of this moss lay along the stems and branches, tightly overlapping, giving them a bloated, fat look, with blunt tips. This feature gives it it's common name: Neat Moss. It's regularly pinnate, so the branches are roughly the same on each side of the stem and they aren't sub-branched. It should have a green stem, if it's red you may be looking at Pleurozium schreberi.

Plageothecium undulatum (play-gee-oh-thee-see-um un-dew-lah-tum)
This is a very easy moss to identify. It forms loose mats of pale green, flattened stems, usually unbranched. If you look very closely at the leaves they are undulate: in other words, wavy from end to end. Hence the common name: Wavy Flat-moss.

Having got that out of my system I can go back to talking about bats...

There is unfortunately no good field guide to mosses and liverworts currently available. However, the British Bryological Society are working to rectify that. You can view the whole of their new field guide on-line (but be aware it's a work in progress):

In the meantime, Carol Crawford has published a very nice guide to common woodland mosses, and it's not expensive (£6.50): Carol L. Crawford (2002) "Bryophytes of Native Woods" (3rd ed.) Natural Resource Consultancy ISBN: 0-9543795-0-0

Many thanks to Nick Hodgetts, David Chamberlain, Alex Lockton and Sarah Whild, without whom I'd still be asking "what's that little green squishy plant?" Incidentally "Right diddly-wotsit squirrelly" was my daughter's exasperated response when I tried to teach her some bryophytes...

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Thursday, 6 March 2008

The name of the bat

I can't help thinking that the English language has failed to play fair by the bat. I mean what sort of word is "bat" to describe such a graceful, enigmatic and fascinating animal? The one distinction the word has is that it was given to a Royal Navy destroyer, HMS Bat, built in 1896. HMS Bat served in the Mediterranean and in home waters during the First World War, before being sold for scrap in 1919. The name was revived during World War II for a naval tug.

So where does this odd little word come from? It is thought to be derived from the middle english word for the bat: bakke, possibly as a result of confusion with the latin word for a night-flying insect: blatta. Bakke itself is likely to be a shortened version of the old Danish word for a bat: natbakka, or "night flapper". Sticking with our Scandinavian forebears, the old Norse had a wonderful name for them: leorblaka, which means "leather flapper". That name must come from someone who had seen a bat's wing close up. It's such an evocative name it's almost worth reviving it!

Other forebears of ours (an awful lot of old races contributed to Britain over the years) also had some interesting names for the bat. The old english word for bat is hreremus (pronounced rear-mouse), meaning "shaky mouse". Whoever came up with that name had certainly watched a foraging pipistrelle!

When the Romans came to Britain they brought the latin word for bat: vespertilio, derived from vesper, their word for "evening". From this comes the family name for all our British bats, apart from the two horseshoe bat species: vespertilionidae. It's also the original root for another bat word. In old Italian vespertilio became vipistrello and thence the modern Italian word for bat: Pipistrello, which of course led to Pipistrelle.

Other modern European languages have interesting names for bats. The Germans say fledermaus, literally "flying mouse". For an ecologist, trying to convince people to live in harmony with bats, it's a little disappointing that so many names for bats refer to mice, at risk of tainting bats with their image as vermin. I suppose it's inevitable.

The French use the word chauve-souris, which translates literally as "bald mouse" This seems odd, until we discover that it's derived from the ancient Greek calva sorix, meaning "owl mouse", which makes more sense.

For me the prize must go to the Spanish. Their name for the bat is derived from the latin mures caeculus or "blind mouse". That's bad on two fronts, as the bat is neither blind nor a mouse, but all is forgiven, because in modern Spanish the word becomes murcielago, the name given by Lamborghini to one of the fastest and most lavish supercars in the world. That's more like it! 

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Monday, 3 March 2008

The Versatile Bat Detector

The most basic tool of the trade for a bat worker must be the heterodyne bat detector: the pocket-caculator look-alike that allows us to listen in to the sounds made by bats. Not only does it help us find bats, it often allows us to identify them to genus or species, to tell when they are feeding and to hear their social calls. It would be easy to be satisfied with that little lot, but the humble detector has other uses too.

Being pedantic, "bat detector" is the wrong name for the machine, as it implies that all you will hear on it are bats. This may stem from our tendency to talk about ultrasound as though it were something special and magical. In reality, ultrasound is simply sound above about 20kHz in frequency. The only thing that sets it apart from sounds below that frequency is the fact that one rather arrogant species with an abysmally poor hearing range can't hear it!

Many everyday things produce ultrasound: pouring water creates a loud noise around 40kHz. The standard test of whether a detector is switched on is to rub your fingers together in front of the microphone, a sound which is much louder around 45kHz than it is at frequencies within our hearing range. "Dry", rustling sounds tend to be much louder at higher frequencies: when our alsatian jumped into a huge pile of dead leaves behind me whilst I was using a detector with headphones, I though I was going to be deaf for life...

Bats aren't the only species which produce ultrasound. A common summer hedgerow sound is the high-pitched, furious squeaking of squabbling shrews. The lowest frequency of that call fall just withing our hearing range (older people may struggle to hear it at all), but on a bat detector tuned to about 20-40kHz they are very clear. In 2005 I and some colleagues from the BATML project were conducting a series of surveys along the towpath of the Union Canal. We kept hearing shrew sounds from one particular place by the water's edge. It was noticeable because these calls were extremely loud and unexpected. When you've had cause to swear loudly at something, it sticks in your mind! The Mammal Society were running their nationwide Water Shrew (Neomys fodiens) survey at the time, so I placed some tubes, baited with casters (blowfly pupae) and sure enough, the scats left in them were confirmed as having been left by a Water Shrew. This was particularly nice as it was the first record of this species from the Lothians for almost 20 years.

Another branch of natural history in which bat detectors are increasingly finding a place is in the study of Orthoptera: grasshoppers and crickets. It is possible to accurately identify them to species by listening to their sounds. Although many can be heard with the naked ear, they are clearer and louder when heard on a bat detector. Unlike bat (or shrew) calls, these sounds have no frequency variation, as they are stridulations, rather than calls, i.e. the sounds are made by rubbing legs together. Identification is made by listening to the rhythm of the sounds. As the insects tend to stay in one place whilst stridulating you can use the detector as a direction-finder to home in on them.

There's a good introduction to Orthoptera id using a bat detector on the web-site of the Environmental Records Centre for Cornwall and the Isles of Scilly (ERCCIS), along with a lot of other useful resources:

The Mammal Society's water shrew survey page:

The Bat Conservation Trust (BCT) website has a guide to choosing a bat detector. The models mentioned are mostly out of date now, but the technical advice is very sound:

For what it's worth, I rate Bat-Box detectors as the best. They have the ideal balance of cost, effectiveness and sturdiness in the field. They're slightly cheaper if you buy direct:

My website: