Thursday, 22 May 2008

Ten Things Every Duet Owner Should Know

Last night I was surveying for emerging bats that didn't emerge, so I had plenty of time to think about life, the bats and everything. It occurred to me that the detector I was using, a Bat Box Duet is of the most popular detectors on the market, and rightly so. It's sensitive, selective, ergonomic, robust and sensibly priced.

As with any piece of equipment, there are hints and tips that help the user, some of which I've picked up from other users and some I've worked out myself. So here are my ten top tips for using a Bat Box Duet:

1. Try plugging your headphones into the tape socket, instead of the headphones socket. You will hear the heterodyne detector in your right ear and the frequency division one in your left. Whatever frequency the detector is set to, you will still be aware of bats on other frequencies. The audio level is fixed, so the volume control has no effect: if you're beside a road or river you may struggle to hear over the background noise.

2. If you want to try this technique somewhere where there is some background noise, try plugging the detector into a minidisc machine and plugging your headphones into the minidisc. You should hear the audio from the bat detector and the minidisc volume control will allow you to hear it louder. This is good practice when recording, as it allows you to be confident that the detector output is being recorded properly. It's very frustrating to get to the end of a survey and find you've recorded nothing because you accidentally knocked the stop button or a plug has come out.

3. When the low battery BAT warning appears on the display, don't panic if you haven't brought a spare battery: the detector will continue to function for a short while. Eventually the frequency indication will go haywire and then the detector will switch off the display to save power, but the detector will still operate for a little while longer.

4. Even in that situation you can by without the frequency display. Although you don't know what frequency you're tuned to, if you rub your fingers together, this sound will be loudest at 40kHz, giving you a very rough frequency indication. Of course, its a lot easier just to carry a spare battery!

5. Have you ever wondered why a seemingly random digit appears when you first switch the detector on? This is the software version.

6. If you have a childish sense of humour (like me) you can convince gullible people you have a very clever detector. Using a worn battery, turn the volume high, without headphones. The loudspeaker is the most power-hungry part of the detector so, when a bat is picked up, the extra current consumption will cause the word BAT to appear. When the call ends, the word disappears again. Fun for all the family!

7. Fed up tuning up and down, to ensure you don't miss any bats? Try tuning to 42kHz. You'll hear Myotis calls as a regular machine-gun type call, Common Pipistrelles as an irregular, thudding and Sopranos as an irregular squeaky sound. Noctules can be hear when close, as this frequency is close to the first harmonic of their call. For heaven's sake don't try this for anything important: you will lose a lot of sensitivity, and you may miss something important (especially Horseshoe bats) but it's handy if you just want a general idea of what's happening. I sometimes do this when I set up a Duet on a tripod to record the frequency division output. In that situation I know everything is being safely recorded, so missing the odd call is less important.

8. Did you know there have been some subtle changes in the design of the Duet since it first came out? Earlier versions had a less sensitive microphone, which looks like a small black plastic grille. the later, more sensitive microphone looks like a tiny metal disc, surrounded by a rubber grommet.

9. Another change is the function of the REF button. In earlier versions this produced a steady reference tone. With more recent Duets, this button shunts the microphone to normal audio. This is handy for taking field notes, as anything you say into the detector will be picked up on the left-hand stereo track and recorded (assuming you are recording the survey). Be sparing in it's use: whilst you are talking the frequency division detector is inactive.

10. I only had nine things, so for number ten I'll mention that the Bat Box III has now been revamped into the same style of case as the Duet. I have yet to get my hands on one, but I suspect it will be a very good heterodyne detector. The original Bat Box III was excellent, but it's only weaknesses were poor ergonomics and difficult frequency indication. The new version (Bat Box IIID) fixes both of those issues and will probably be a really good little brother for the Duet.
The Stag Electronics (Bat-box) website:

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Wednesday, 21 May 2008

A Bat in the Hand....

...takes a great deal of work to achieve!

In company with a small group of people from Lothians and Scottish Borders bat groups I attempted to try out my new harp trap last night (see "The Kitchen Table Harp Trap", under February 2008).

The site was a ruined castle, set in a secluded valley in the Scottish Borders. "Ruin" is probably the wrong word, as the seventeenth century noble who set about building it never completed the job but, with massive stone walls up to 50 feet high, it really looks the part. Barrel-vaulted cellars with plenty of deep gaps and cracks in the stonework provide good roosting opportunities for bats. There are woods and a river close at hand, providing foraging opportunities for several bat speices and in the past we have trapped Natterer's Bats (Plecotus nattereri), Daubenton's (Myotis daubentonii) and Brown Long-eareds (Plecotus auritus).

Trapping bats is enjoyable, but there needs to be a valid scientific reason to interrupt the bats in their normal activity. On this occasion bats were to be rung as part of a long-running study of bats using sites of this type in the Scottish Borders. In addition, I was planning to remove parasite specimens as part of my studies into their distribution and host associations.

Two harp traps were put in place: mine and a slightly larger one, each covering the entrance to one of the cellars. There is an art to siting a harp trap: it needs to cover as much of the entrance as possible and gaps need to be filled as far as possible, to prevent bats flying round the trap. A tarpaulin, some leafy twigs and an old coat were pressed into service around my trap:

It was quite cold, dipping as low as 5 degrees centigrade after sunset and bat activity wasn't high, apart from the large numbers of Soprano Pipistrelles (Pipistrellus pygmaeus) dispersing from their roost in a nearby farmhouse. Nonetheless, we caught four male Daubenton's, all of which emerged from one of the cellars. Frustratingly, it wasn't the cellar which had my trap at the entrance!

Two of the bats were recaptures and had been rung on previous visits to the site, but the other two were new and, as well as being weighed and having their forearm length measured, each had a tiny numbered aluminium ring slid onto it's forearm.

None of the bats had many parasites. This is often the case in spring, especially with adult males, which usually carry a lower parasite burden than females and juveniles. They are able to move between roosts to avoid parasite accumulation, whereas the females and juveniles are together in the maternity roost for several weeks each year, often with many other bats. I like to think that juvenile bats may also have similar personal hygiene issues to many human teenagers!

The picture above shows the fouth bat to be caught, who caught my interest as he had a tromiculid mite larva in his ear. The Trombiculidae are a large family of mites, including members of the genus Leptotrombidia, which parasitise bats for part of their life-cycle. Their larvae hatch within a bat roost, climb onto a bat and attach themselves, often in the bat's ear or on the forearm. There they take a meal, before dropping off the bat to become predators of other small arthropods within the roost during their nymph and adult phases.

I was particularly interested, as there are very few records of these parasites on British bats, partly because records of any bat parasites are rare and partially because they can be difficult to remove. Fortunately, this bat was quite placid and, with Carol-Ann (the "bat whisperer") holding him, I was able to paint the mite with a little isopropyl alcohol using a very fine brush, to make it release it's grip, and then remove it with fine soft forceps.

Once home I checked and have been unable to find any records of a trombiculid mite on a Daubenton's bat in the UK (unless anyone reading this knows better?), although that doesn't necessarily make it a rare species: probably just an under-recorded one. It will probably be a while before I am able to positively identify it to species: there are no field guides!

I haven't mounted the mite yet, but here's a rough and ready picture taken at x120. The larvae are usually a distinctive orange colour when seen on a bat. With their mouthparts buried in the bat, they look like tiny orange jelly beans.

As for the harp trap, it is still waiting to be christened with it's first bat. Watch this space...

Please note, trapping and handling bats without proper equipment, training and experience can be very harmful. Furthermore, in the UK it is illegal to do so without appropriate licences from Scottish Natural Heritage, Natural England, the Countryside Council for Wales or the Environment and Hritage Service in Northern Ireland.

If you're interested in getting involved in working with bats, the best starting point is your local bat group:

A checklist of mites found on British bats can be downloaded here:

My website:

Thursday, 15 May 2008

What is it About Bat Surveys...?

Maybe it's the peculiar hours that bat-workers keep, or maybe it's the association with unusual animals, but there's a definite tendency for odd occurances and very odd characters to be encountered whilst doing bat survey work.

The people we meet range from the scarily enthusiastic, through the utterly barking and the dangerously misinformed to the simply peculiar. On one survey for Daubenton's Bats alongside a canal a bewhiskered Wing Commander type approached me and barked an enquiry as to what we were doing. When I told him he replied "That's alright then: I thought you might be looking for otters." I should probably have extricated myself there and then, but my curiosity got the better of me and I asked why he might ask that. In return I was treated to an extensive diatribe on the evils of the poor otter: how it kills lambs, despoils the countryside, wrecks fishing and probably bears off virgin maidens, causes global warming and harbours Osama bin Laden in it's holt. Where he had got all this rubbish from wasn't clear but it was obvious from the gleam in his eye that his opinions weren't open for discussion and I beat a hasty retreat.

On another occasion I was carrying out a dawn survey in a small park in Livingston, not a town noted for it's ethnic diversity. Just before dawn an enormous black gentleman jogged purposefully towards me, wearing colourful, flowing West African robes and fez hat and carrying a huge carved staff. He padded past me on bare feet without a sideways glance. Ten minutes later he returned in the opposite direction, still with the same purposeful, steady gait and again he acted as though I wasn't there, leaving me wondering if I was dreaming (at 4.30 in the morning that's entirely possible!).

In a town noted for it's UFO sightings I had to attend to a remote bat detector with odd noises emerging from it's radio receiver. When I reached it, I found two men with the case of the detector open, staring at the electronic gadgetry inside. I introduced myself and asked what they were doing. Their candid reply was that they though it might be a bomb, so they had opened it to see. What degree of utter stupidity led them to decide that it was a good idea to open a suspected bomb? Then again, perhaps they had a point: an Anabat detector belonging to the Highways Agency was recently destroyed by the Bomb Squad in a controlled explosion after it was found attached to a motorway bridge.

It's sometimes hard to understand chiropterophobia (or fear of bats), but for those it affects it is a very real problem. Last year I was checking a heated bat box on Ministry of Defence property. The sergeant on duty was built like the proverbial brick sh**-house: his muscles probably had muscles and I had no doubt that he could probably kill me with his little finger, whilst drinking a mug of NAAFI tea with the other hand. Nonetheless, it seemed a good opportunity to attempt some bat PR, so I explained what we had found and tried to show him a photograph on my camera. In a trice he was on his feet, backing away and shaking. I swear, if I hadn't calmed him down he would have reversed straight though the wall.

I was recently asked to look over some derelict council flats for any signs of roosting bats: a long day of methodically working through attic after attic. I expected them to be empty, as the occupants had long gone, but almost every attic was a treasure trove of the weird. One contained a knitting machine and enough wool to keep a knitware factory supplied for months. Another contained most of the body panels for a Ford Escort. Even odder was the attic in which several hundredweight of soil was lying in heaps, reminiscent of the PoW hut roofs in The Great Escape. Why? How? Your guess is as good as mine.

In case anyone reading this is feeling put off bat work I should stress that the odd situations and people are outweighed many times over by enormous numbers of warm-hearted, helpful and interested members of the public.... but the other sort are far more entertaining!

Please remember that some of the bat work described here requires a licence, issued by one of the four statutory nature conservation organisations. It is an offence to disturb bats or their roosts without one.

My website:

Dawn Swarming

Someone once said that bats are hard to study "...because you can't see them and you can't hear them." It's certainly true that they don't give away their secrets easily, though bat detectors have allowed us to start the long hard job of understanding them.

A behaviour exhibited by most British bats which tips the balance a little on our side is dawn swarming, in whcih bats returning to a roost fly around the roost entrance for a period of time at dawn, often making false landings at the roost entrance. In doing so they give away the roost location. This is in stark contrast to evening emergence, when they dive out of the roost, flying hell for leather to avoid any possible predators, making it hard to spot where they have emerged from!

Of course the downside is that dawn is a horribly antisocial time of day to be about, something I was reminded of when my alarm clock went off at 2.45 am this morning. With dawn in Edinburgh at 5 am I wanted to be alongside a roost site at a suburban house well beforehand, to watch swarming develop. It wasn't just for fun: I had a suite of things I needed to know about these bats. All I knew was where the roost entrance was: at the end of a flat roof bargeboard, giving access to a hollow wall; and that they were Pipistrelles. I needed to find out which species they were, whether they were roosting in any other parts of the building and approximately how may bats roosted there.

For the first half hour there were steady comings and goings, with Soprano Pipistrelles (Pipistrellus pygmaeus) entering and leaving the roost in small groups and occasional bats flying close to the entrance in twos and threes. At 4.25 am swarming started, with numbers gradually building up to a peak five minutes before dawn, with around 60-70 bats zooming round the adjacent garden. You can see a brief snippet of the action here:


Soon after this bats started to enter the roost. Up until this point, everything was as I expected: no other part of the house roof was involved, I knew the species of bat and could see an approximate number. All I had to do was count them as they entered the roost, giving an accurate count and the job was done...or was it?

Only 30 bats actually entered the roost. The remainder gradually gained height until they were around 5-10m higher then the house, then one by one they flew off to the north-east. I have never heard of this behaviour before and was quite astonished to see it. Stuart Smith, of Lothians Bat group was later able to tell me of another roost site about half a kilometre away in that direction, so perhaps that is where they were heading. It is quite common for a colony to move around between several roost sites, but I have never before heard of them swarming at one site and then splitting up, to roost in mor than one location.

Whatever the cause, it was worth being up early to see the spectacle: the video doesn't really do it justice!

My website:

Thursday, 8 May 2008

The Hunting of the Noctule

For some time I have been rather fascinated by Noctule bats (Nyctalus noctula). One of Britian's largest bats, they emerge from their roosts earlier than other species and fly high abve pastures and river valleys, dipping down to catch larger insects. With a very loud call (reputedly louder than the legal safe limit for audible sound), their distinctive "CHIP CHOP" can often be heard from several hundred metres away.

You can hear a Noctule here:
(It was recorded in the Scottish Borders, using a hetereodyne bat detector set to 22kHz).

Traditionally they have been assumed to be largely absent from Scotland, apart from Dumfries and Galloway. It has been known for a while that the occasional Noctule turns up in the Scottish Borders and that there is a small population in the Tweed valley. More recently, there have a handful of records from reputable sources of Noctules in the Lothians, which led some bat-workers to query whether they are more widely spread than previously thought.

I set out to try to clarify this, by gathering together records from many sources across the Lothians and Borders area. I eventually gathered 41 records, from across the region, ranging from audio recordings validated by reputable ecologists to visual records of "large bats". That sounds like a lot of records, but they range over a period of eight years and twenty of these records relate to just 4 sites.

You can see a map of these sites here:

Hoping to locate more of these bats, I decided to use a variation on the car survey method, used for the Bat Conservation Trust Bats and Roadside Mammals Survey. This very successful technique involves driving at twenty miles an hour along country roads, with a bat detector poking out of the window, allowing many records to made in areas where bat-workers are thin on the ground (See below for the detailed method).

My theory was that, by doubling the speed to 40mph, a lot of ground could be covered in one session: typically 80miles in a session. The Noctule is a loud, high-flying bat, so mounting the detector on the roof and travelling faster should be feasible. The detector could be linked to the car stero with a wireless link, so that it's output would be clearly heard and we could stop and investigate when we heard anything suspiciously Noctule-ish. Thus, two nights ago, with Nigel acting as navigator, we set off in a vehicle decorated with rotating amber beacon and reflective warning sign to drive down the Tweed Valley and test the theory.

It was a perfect evening for bats: warm, dry and with plenty of flying insects around. We encountered an initial problem with air moving over the detector's microphone, causing unacceptable levels of background noise. This necessitated a speed reduction down to 30mph, after which the system seemed to work well and we soon started to hear Pipistrelles.

As a slight cheat we paused by the Dryburgh Suspension Bridge at Newtown St Boswells, a spot where there is usually a Noctule or two. Sure enough, a Noctule flew past and we could clearly hear it. Further on we crossed the Tweed at Coldstream and, after negotiating an unexpected diversion we found another bat near Wark. This was certainly a Nyctalus bat, but it is just possible it could have been a Leisler's Bat (Nyctalus leislerii). We heard only a couple of brief passes and the Leisler's has a similar call. Typically, we had two hand-held detectors linked to minidisk recorders and both failed at the same time! Without a recording to analyse and verify the bat's call we have to simply call it Nyctalus sp. Nonetheless, it proved that this variation on the BCT method is effective and worth persevering with.

You may ask, why not use the standard method? Firstly, 20mph is simply too slow to cover the vast amount of ground we need to survey and 30mph appears to work with these louder, high-flying bats. Secondly, the standard method requires some very expensive equipment and teams of four people, both factors which could be limiting. That in no way negates the amazing work that has been achieved by people in the UK, Ireland and elswehere using the BCT method.

The plan is now to carry out more surveys this year, focussing particularly on habitat that seems likely to be suitable for Noctules. To avoid making the same mistake twice, the audio from the roof-mounted detector will be fed via a lap-top, so that a permanent record can be made.

Anyone fancy a drive in the country?....

The standard method:

My web-site:

Spring Has Sprung....

Three weeks ago I asked whether spring was springing yet, at least in terms of bat behaviour. We can safely say that Spring has now sprung. The chart below shows the night-time temperatures at Gogarbank meteorological station, near Edinburgh, since 1 April. It clearly shows that, after a brief blip at the start o last month, followed by a colder period, the warmer weather is now settling in.

(Met Office Data)

Last night Lothians Bat Group members returned to Blackford Pond and we found a big difference to the events of three weeks ago. For a start, we didn't have to tiptoe through hordes of amorous toads! Of more interest to us was the big increase in bat activity. At least 4 or 5 Daubenton's Bats (Myotis daubetonii) were foraging over the pond and finding plenty of invertebrates to eat. Above the footpaths were many Soprano Pipistrelles (Pipistrellus pygmaeus) and one or two Common Pipistrelles (Pipistrellus pipistrellus).

Whilst we were there, I was able to hook a frequency division bat detector up to a lap-top running Batsound software alongside the pond. Newer members of the group were able to see sonograms of the common species and compare them with the sounds, to help get a handle on the basics of bat call identification.

To give a flavour of the evening, here's a brief video clip showing two of the Daubenton's Bats over the pond last night. You can hear a heterodyne bat detector in the background.


We mustn't leave out the Pipistrelles: the most charming and delightful to watch of our native bat species. Here's a very short clip of a Soprano Pipistrelle feeding just before dawn this week, at another site in Edinburgh.


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