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23 May 2005
Bats—The Missing Link In Insect Control An Australian wildlife ecologist’s research over the last 25 years has revealed the rich diversity of insect-eating bats across Australia’s southern state of Victoria and discovered that bats play a much larger ecological role than anyone had imagined, probably eating more insects than birds do.
TRANSCRIPT: BLANCH : Well, farmers can reduce the need to spray their crops with insecticide by encouraging insect-eating bats to roost in old hollow trees in their properties says an Australian wildlife ecologist. Dr Lindy Lumsden’s research over the last 25 years has revealed the rich diversity of insect-eating bats across Australia’s southern state of Victoria and discovered that bats play a much larger ecological role than anyone had imagined, probably eating more insects than birds do. In the course of her research Lindy has developed much innovative technology that is now being used by bat researchers worldwide including a system for rapidly analysing thousands of bat calls. Well Lindy, they don’t quite call you Bat Woman, but it’s a name that would be apt and there isn’t much you don’t know about bats and their role in the environment, but you’ve uncovered the role of bats in insect control, hence your suggestion that farmers retain old trees with hollows on their properties. Now how small or large are these bats and what volume of insects can they consume? LUMSDEN : Yes all the bats that we get in southern Australia, and it’s the same all around the world, most of the bats are the small insect eating bats and often they’re tiny. The smallest one we get in Victoria is only four grams which weighs less than a ten cent piece and could fit inside a matchbox, so they’re really tiny and most people don’t realise that they’re actually that small and these ones are really good because they eat large quantities of mosquitoes which are always seen as a problem and they can eat up to half to three quarters of their own body weight in insects in a night and similar sized ones in North America have been shown to be able to eat about 600 mosquito-sized insects in an hour. BLANCH : So how many varieties have you identified so far? LUMSDEN : In Victoria we’ve got 21 species of insect eating bats, but across Australia there’s many more and throughout the world there’s even more still, so I’ve been lucky enough to do some work elsewhere in Australia and also overseas and so got to see a whole range of species which is fantastic. BLANCH : Well, you spent a lot of time out there in the wild, so to speak, how do you measure bat populations? I mean it must be rather difficult as they hunt silently to our ears anyway and they do it at night. LUMSDEN : Yes they’re quite a hard group to work on because they are only coming out at night, they’re hidden during the day in roosts, but the tree hole roosting bats can be spread across a whole area and virtually impossible to count and to work out how many are there, so we need to use a whole lot of modern technology to be able to even study these animals because we can’t hear them, we can’t see them, we can’t count them, so by using new technologies, we’re starting to get a handle at least on comparative levels of activity and abundance. BLANCH : Well, you and your colleagues have developed an automatic analysis system that can do in hours what previously took months, so what did you develop? LUMSDEN : It’s using a system called the Anabat Bat Detector and this is a unit that’s been developed in Australia, but now is sold all around the world, so it’s a great way of recording a whole lot of bat calls because all of these species are making calls that are outside our hearing range. We can hear up to about 15 kilohertz, but a lot of these bats are calling up to 60 or even 100 kilohertz. So this unit enables us to record those calls, but then people used to manually identify them, so by looking at each call and trying to look at the shape and the frequency, be able to work out what the species is, but we’ve developed a system that we can develop keys for each individual species in an area and then by putting this in some specially designed computer software, be able to run through using this automated key and like you say, analyse 40,000 calls in a couple of days rather than taking four or five months. BLANCH : So how does it all work? LUMSDEN : Well, you need to get good recordings of each species of bat for a region, so when we use the bat detector what it sounds like if it’s divided down to within our hearing range - I’ll just show you what fingers making a noise on a bat detector sound like …(SFX tick tick tick) so that’s just fingers making a noise because when you rub your fingers together that puts out a high frequency sound, but I’ll play you what a real bat recording sounds like. So this is a bat that’s been flying around calling maybe at about 60 kilohertz and this call has been brought down to about four kilohertz that we can hear … sfx bat sounds BLANCH : And you can tell from that what bat it is? LUMSDEN : Not from listening to it audibly – all of them sound fairly similar, but by downloading those calls and then putting it into this analysis system, yes we can tell what species of bat it is from that call. BLANCH : What’s the story of developing this technology? LUMSDEN : Well, it’s largely come out of trying to be able to study these bats that are so hard to be able to study. The guy that originally wrote the Anabat developed the detector and the software, was somebody that had some hearing problems and he works a lot on birds and he just thought ‘gee, it would be interesting to know what bats sound like and I can’t hear them, so maybe I’ll develop some equipment to be able to analyse them’ and this guy Chris Corben who developed this initial work – he’s just fantastic. He just developed all of this system to be able to record these calls and then here in Victoria we’ve tried to take it that one step further to be able to rapidly identify the calls, because on any one night I could maybe record several thousand calls and to try and look at each one of those individually just takes a huge amount of time. BLANCH : But not anymore? LUMSDEN : Not anymore. BLANCH : So how many bat calls do you now have on tape? LUMSDEN : I haven’t actually counted them up, but many hundreds of thousands. BLANCH : Forty thousand? LUMSDEN : Well, forty thousand just from one study, so probably closer to 400,000. BLANCH : Well, let’s have another listen to some of the sounds of these insect eating bats and you can perhaps tell us what they’re doing as they’re making their sounds. LUMSDEN : So this particular one is a bat that’s cruising around searching for insects and the call starts off fairly slow and then as it picks up that there’s an insect in front of it, it rapidly increases the rate of its call and changes the shape of its call to get a really, really clear picture of the insect so it goes into what we call a feeding buzz where it does a very rapid sort of shooomp to get a really clear picture and it can tell from that what type of insect it is – whether it’s one that it likes to eat or one that it doesn’t , whether it’s poisonous or not poisonous, whether it’s the right sort of size and get a really, really detailed picture of where exactly it is so that it can catch it. Bat call. BLANCH : So that’s a feeding buzz, but are there ones that sound quite different? LUMSDEN : Yes there are some species called Horseshoe Bats or Leaf Nosed Bats that have got a totally different shaped call – they’re called constant frequency where most of their call is at the one frequency rather than starting high and dropping low and their calls sound really different and I’ll play one of those for you now. Horseshoe Bat call. BLANCH : When you’re trying to analyse these bats, do you have some that say aren’t in the region, might just be visiting, I mean how far do they travel? LUMSDEN : Individual bats can move fairly big distances on a nightly basis, so I’ve had some of these little bats moving up to 15 kilometres at night between where they roost and where they feed, so we get those sorts of movements, but then some species will also migrate and they might move a couple of thousand kilometres, so we need to take that into consideration as well. And then there’s the occasions where we might get a vagrant turning up, so an animal that might normally occur in northern Australia, but occasionally shows up in southern Australia, so if we know that that’s happening we can include all of those species in the key and then if they happen to be there, we’ll identify them. BLANCH : So what kinds of problems do bat researchers around the world face, I mean are they similar to what we have here in Victoria? LUMSDEN : Certainly is, because these small insect eating bats are quite similar all around the world - we get different species and you know, slightly different habits and different families, but a lot of them are doing similar sorts of things so it’s the same sort of problem that we need to be able to record animals that are flying around at night that are silent to our ears, so it’s the same issue faced by researchers in North America and Europe and everywhere else in the world. BLANCH : So how would they apply this technology to a region say in Borneo or America or where? LUMSDEN : Yes very easily. As long as the people using it were familiar with their bat fauna in the region. It couldn’t be used by somebody that was totally new to doing research on bats without developing regional reference libraries so that you knew exactly what each species of bat sounded like, so you basically need to know what species are likely to be in the area and what their calls sound like to be able to feed into this system, but you know, there’s lots of bat researchers around the world that have got that expertise that could use this equipment. BLANCH : So when would you hope to have this kind of system commercially available? LUMSDEN : Hopefully over the next couple of years. It’s something that’s still being refined at the moment, but we’re hoping that it will be available to people because it is a great new system that just saves a huge amount of time. BLANCH : Dr Lindy Lumsden from the Department of Sustainability and Environment at the Arthur Rylah Institute in Melbourne with an intriguing insight via clever technology into the until now silent world of the micro bats – some so small then when placed on your thumb tip make your thumb look huge. Back |
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