Connecting Bat Detectors to Audio Equipment

This is the time of year when bat survey equipment starts to get dusted off and checked over, ready for the new survey season. Top of the list of course is the bat detector ( I can't even begin to understand what it must have been like to survey for bats before portable detectors was available).

Many bat-workers make recordings of bat calls they hear in the field, either so they can have a second attempt at identifying a bat at home, with a glass of something warming or, in the case of frequency division or time expansion detectors, to look at calls using Batsound or other call analysis software. I thought this would be an opportune moment to look at the connections between the detector, the recording equipment and the computer. It seems simple enough, but there are a few easy errors, which are less obvious than might be expected.

To understand how to connect things properly we first need to understand a couple of techy things about jack plugs and sockets:

Jack Plugs
There are several types of audio jack plugs, but virtually everything we are interested in uses 3.5mm jacks. There are two types: mono and stereo. The stereo plug is connected to three wires: one common and one for each of two audio channels (normally used to create that "close your eyes and visualise the orchestra" effect by producing slightly different versions of a music track in each ear). The mono plug has only two wires and, you've guessed it, only one audio channel.

Where it gets slightly tricky is that the mono and stereo jacks are the same size and fit into sockets intended for one another.

Sockets
There are four types of audio socket found on bat detectors and recording equipment:

1. Audio out (also labelled as headphone or speakers) is the socket on the detector or recorder which squirts out sound. The level is controlled by the volume control.
2. Line out (often labelled record) is the same as audio out, but with a steady volume, unaffected by the volume control.
3. Line in (also called audio in or sound input) is the socket on the recorder or PC through which the equipment receives audio.
4. Microphone in is similar to audio input, but is easily overloaded, as microphones produce very low level audio.

That's the geek stuff over. So, why does it matter? Most bat detectors are mono. As the two types of jack plug are interchangeable it doesn't really matter which we use. In fact it's helpful that they're interchangeable as it means stereo headphones can be used. A bog-standard stereo jack to stereo jack lead can be bought at Comet to connect the detector to a digital audio recorder, minidisc recorder or cassette recorder. Incidentally, avoid cassette recorders: the tape speed falls as the battery runs down, turning Common Pipistrelle calls into Nathusius' ones.

It's always advisable to connect the line out soocket on the detector to the line in socket on the recording equipment. That way, the machines take care of the audio levels and we can get on with looking at bats. Life being the way it is, some machines don't have these sockets, so we have to get a bit sneaky.

If there's no line out (or record) socket on the detector, it's necessary to use the headphone socket (and plug the headphones into the recorder's headphone socket, so we can hear what's happening), but it's necessary to make a few experimental recordings to work out what level the detector volume needs to be set to, to produce the clearest recordings.

If there's no line in on the recorder then it's necessary to use the microphone in socket, taking care not to overload it by having the detector volume set too high. The recorder's automatic level control will cause the background white noise to increase when there;s no sound, but it should drop the moment a bat is picked up.

The Bat-Box Duet
Things get more complex when using a Duet. These are excellent detectors, allowing the user to listen to a heterodyne detector, whilst recording what the user hears and the sound from a frequency division detector, one on each stereo channel. This permits later computer analysis. Admittedly, the sonograms produced are not quite as perfect as those made with recordings from a time expansion detector, but they're usually good enough for most purposes and it's much easier to use (anyway, how many hobby bat-workers can afford to pay a grand for a time expansion detector?)


The Duet achieves it's cleverness by using the two stereo channels: left for the frequency division audio and right for the heterodyne audio. As long as the recording equipment is also stereo then a standard stereo jack to stereo jack lead can be used. However, some digital audio recorders only have a mono microphone input. If you put a stereo jack in here the machine will record a weird amalgam of the output of both detectors. A cable which splits the stereo into the two mono outputs is required - see below. You need to go to a specialist shop like Tandy or Maplin, or if you're handy with a soldering iron, make one yourself.

The other difficulty comes when you replay the bat calls into a computer. If you don't have a line in socket on your computer the microphone socket may work, but it will be mono, rather than stereo, so the same cable is required.

Incidentally, if you're buying a minidisk recorder for use with a bat detector, check the line in socket carefully. Most have some sort of audio input, even if there's no line in socket, but a generation of minidisk players exists where the line in socket is a weird digital thing which looks like a 3.5mm jack socket, but simply doesn't work, except to record from other digital equipment.

Of course, all this should soon be academic, as we move towards bat detectors with built-in memory cards. Hopefully that will make redundant the geeky knowledge I acquired from my youth, spent making dodgy cassette recordings of LPs......

The BCT have published a useful guide to recording with digital equipment: http://www.bats.org.uk/helpline/documents/Digitalrecordingwithbatdetectors_005.pdf

More about the Bat-Box Duet: http://www.batbox.com/duet.html

My website: plecotus.co.uk

Finally, if you follow any advice here, you do so at your own risk.

Is spring springing yet?

When does Spring start? According to the Met Office, spring starts on 1 March, although the traditional start is the vernal equinox, on the night of 21/22 March. Here we are in mid April, so surely spring has started?

From a wildlife point of view, spring activity starts when the prevailing weather conditions permit, so in truth it's quite a variable thing, not just in terms of date, but geographically. The south of England is likely to experience signs of spring one or two weeks before they appear here in Scotland.

With some members of Lothians Bat Group, I went to Edinburgh's Blackford Pond after sunset, one evening last week. If you live in Edinburgh this is a great place to see large numbers of Daubenton's Bats (Myotis daubentonii) and Soprano Pipistrelles (Pipistrellus pygmaeus) in the summer, and the group usually run a bat walk there every year. On this occasion we wanted to see if there were the first signs of bats emerging from hibernation yet.

With an ambient temperature after sunset of just 2.5 degrees celsius, it was questionable whether we'd see any bats at all, but what was probably a lone Soprano Pipistrelle passed by a couple of times and we watched one, and later two Daubenton's Bats feeding on the pond. There was very little food for them, so they were having to range over the whole of this large pond, to find enough flying insects to eat (they looked to be small Sedge Flies). With such a low temperature, it's possible that these few bats were some of last year's juveniles, desperate for food after the long months of hibernation.

So is it spring? Well, not really from a bat point of view, as it seems like the main population are still in hibernation. The graph below shows the night-time temperatures at the Gogarmor meteorological station, to the west of Edinburgh, since the start of April. As you can see, there was a brief peak of warmer temperatures at the start of the month, but it has been quite cold at night since then.

Having said that, there are other signs of spring. As we walked around Blackford Pond, we had to tread carefully to avoid a large number of toads, commuting towards the pond, in order to mate?

Since then I have also seen some discarded eggshell from what must be a very optimistic bird and last weekend, I watched a group of Brown Hares (Lepus europaeus), boxing and chasing each other: the so-called "mad march hare" behaviour, associated with the onset of the breeding season. This behaviour actually continues through to September, but is far more noticeable just now, whilst the grass is short.

Hopefully we'll get a spell of warmer weather soon, and we'll start to see more bat activity, as the adults move out of their hibernation sites and the move towards maternity roosts commences, ready for the breeding season around June. My bat detectors are charged up and ready...

My website: plecotus.co.uk

"Untold riches" of swarming bats...

I am officially conferenced out, having spent the last three days in York for the
Mammal Society Conference. It was definitely worth going: I'm buzzing with thoughts about Irish hares, Beaver management in Bavaria, small mammal survey trials and much else besides. It's a little disappointing that there were no papers on bats, but that was more than made up for by Professor John Altringham's Cranbrook lecture.

John's team from Leeds University have carried out a large and complex study of bat swarming behaviour at caves in the Yorkshire Dales and the North Yorkshire Moors. Autumn swarming is a behaviour which is increasingly seen as an important part of the annual cycle of bats, especially Myotis and Long-eared species. Bats gather at hibernation sites, usually caves and mines, to check out the site, to help young bats find it and for courtship and mating. Swarming is typified by chasing behaviour late into the night, often peaking three or four hours after sunset and takes place during August to October.

They looked at Natterer's Bats (Myotis nattereri) and, by ringing bats at known summer maternity roosts and then harp trapping at swarming sites, were able to demonstrate that bats wer flying up to 60km to a swarming site. They were also able to demonstrate that huge numbers of bats were using these sites: up to 400 per night, with considerable turnover between nights. Furthermore, by comparing data year on year they were able to demonstrate high fidelity: bats tend to return to the same site each year. The conservation implications are huge: these sites can provide a key part of the lifecycle of very large numbers of bats, from a wide geographical area.

What struck a chord with me was the fact than John described the importance of these sites and went on to mention that it was then usual to find only a handful of hibernating bats within the caves, as many were not visible. In other words, some of the hibernation sites we survey in the Scotland could be swarming sites for similarly large numbers of bats. Not for nothing was one of John's conclusions the possibility of "untold riches" for bat-workers.

This tiny hole, high in the hills in South-west Scotland, gives access to a tunnel over half a kilometre long, which contained 9 Natterer's Bats and 1 Daubenton's. Could this be a swarming site on a similar scale to the ones in the Yorkshire Dales?

Another intriguing part of the lecture related to a study in which John's team compared the numbers of hibernating bats to the physical features of a cave or mine. They found that the size of entrance was irrelevant ("if you can get in, they will"), as was the altitude, the orientation of the entrance and the habitat nearby. What makes a good hibernaculum is large spaces inside, a reasonable depth, some cover near the entrance and not too wet. This struck a chord with me, as we've done several surveys in the past winter of a limestone mine, which seemed to have all the right features of a hibernaculum, but we never found any bats. John's conclusion was "the more water, the fewer bats", which seems to fit.

I must finish by plugging the Mammal Society's new edition of "The Mammals of the British Isles". It's not cheap (and you may need to reinforce your bookshelf to take the weight), but it is worth every penny. If you buy a copy via the Mammal Society website, all ofthe profit will go to the society.

John Altringham's Leeds University web-page: http://www.fbs.leeds.ac.uk/staff/profile.php?

The Mammal Society: http://www.abdn.ac.uk/mammal/

My website: plecotus.co.uk

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.

Find your local bat group: http://www.bats.org.uk/batgroups/batgroups_list.asp

More information on the NBMP: http://www.bats.org.uk/nbmp/index.asp

Lothians Bat Group: http://plecotus.co.uk/page_1204624452640.html

My Website: plecotus.co.uk

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 http://www.butterfly-conservation.org

Another good source of information on moths: http://ukmoths.org.uk

My website: www.plecotus.co.uk