March 2011
New
evidence suggesting that rare short tailed bats are present in
the
Landsborough Valley, in New Zealand, has been uncovered using a unique
bat detection system.Remarkably the amount of work needed to make the discovery only required 3.5 hours work and was done as part of an existing predator control maintenance programme.
The discovery utilized ten TrakaBat detectors developed by Ian Gill (pictured right) from New Zealand.
The detectors automatically test for the presence of bats, by “listening” for bat noises in the environment. Developing a “listening” device in this case actually means tuning the detector to eliminate environmental noise – rain, wind and insects while accepting bat noise.
So how did it all come about? Ian says he first got interested in bats when doing some pest control advocacy work for the Department of Conservation several years ago. "I heard there was very little known about whether or not there were bats in the area I was working in so I asked if I could borrow some detection equipment. I was a bit stunned when a huge device arrived that would have required a wheelbarrow to go on a walk. I declined to use it, and it got me thinking, I bet I could make a better bat detector”.
“I
started out with a basic understanding – that our rare, short
tailed bats,
were going to be very difficult to encounter. I talked to Dr Colin
O’Donnell, who is a legend in NZ bat work, and he told me that in
foraging areas the encounter rate for this species could be as low as
one or two passes in 90-nights. That works out to be a few seconds of
bat passes every 2.6 million seconds. So I knew that the detectors
would need to be left out in the field for a considerable time, they
would have to filter information with intelligence,
and an
array of at least ten detectors would improve the chances of
good
placement."I fine tuned the design down to a size where a number of them are easy to carry and I made them efficient to minimize the person-hours needed to run them in the field. That means that the detectors are small enough to be taken along as part of another job and they run for a long time on minimum resources.
The ease of interpretation of the results was also a key design criteria, a wave of a magnet will tell you yes or no to bat detection and more detailed data can be simply drawn down from the detectors back in the office. That sure beats listening to hours of recordings!
Ian nearly threw the whole project away a couple of years ago when he started getting random noise samples identical to bat echolocation pulses in his yard, but the last bat reports in the area were from the 1960s "When I saw the profiles I thought, oh no, I’ve spent years on this project and it’s not going to work. It was a shattering moment, but, over a cup of tea I thought, hang on - if that profile is identical to a bat - maybe there is a bat making the odd flight here? So, I put out the conventional gear, and sure enough, there was a long-tail bat visiting. ”
Another problem hindering the development was the habit bats have of hibernating. In winter the bats would not fly and Ian could not get the data he needed to adjust the software profiles. This was solved on the other side of the world with the help of international bat expert, Dr Markus Utesc. He put prototype TrakaBat detectors out in Germany during the northern hemisphere's summer months and e-mailed the data records to Ian.
With the development completed it was time to put the Array out in the field and use it.
Ian says the remote Landsborough Valley was a logical place to look for short tailed bats because of its long history of pest and predator control and intact forest.
"A previous survey some years ago had found long tailed bats in the valley and on the occasions when I had been in there I had always come away thinking that short-tail bats could be using the area too
"The question was how to find out, without spending a whole lot of money. So I volunteered to work on the stoat trap programme which put me in the right spot in the valley to deploy an Array of ten detectors over an area of a kilometre.
"The detectors ran for 44-nights and stayed in place for a couple of months until another crew working nearby retrieved them for me. The result was a very exciting 28kHz record from Unit-6 at 23:00 on the 8th December 2010, indicating the presence of short tailed bats in the valley”.
