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: http://www.plecotus.net/noctule.mp3
(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: http://www.plecotus.net/noctuleatlas.jpg
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: http://www.ibats.org.uk/page.aspx?tabid=256
My web-site: plecotus.co.uk
Thursday, 8 May 2008
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.
My website: plecotus.co.uk
Tuesday, 29 April 2008
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.
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.
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:
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.
Tuesday, 15 April 2008
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
Monday, 7 April 2008
"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.
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
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
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