The art of gathering bat reference calls
Updated: Jun 13, 2019
HOW IT BEGAN
When I was a kid I was fascinated by bats. We only had microbats in our area, so the most I saw of them was a silhouette in the dusk sky or a passing shape in the illumination of a street light. One time I even remember a bat roosting under the eaves of one of the high school buildings. Mysterious creatures cloaked in the darkness of night, it's no wonder people have treated them with suspicion. Thanks to modern technology we can look further into the world of bats and show the public that these amazing, intelligent creatures are worth having around and are not just important but vital to our ecosystems and many of the goods we consume.
Here at Enviropixel we have a range of equipment that sheds light into the world of bats. The Echo Meter Touch 2 PRO records and displays bat calls for easier identification while a night vision camera can view bat emergence from roosts and the electronic harp trap (in development) is about the size of a regular harp trap (but way lighter and more portable) but doesn't catch bats - photographing them instead as they fly along paths or come down to drink. When we use these devices together, we can gather vital information such as reference calls, record peak feeding times and so much more- without capturing or disturbing bats any more than absolutely necessary - usually not disturbing them at all. And it doesn't require ethics approvals or licences as we are simply observing! Clearly this is a win-win.
GETTING THE BAT REFERENCE CALLS
I had been experimenting with a variety of home made devices to capture bat images out in the wild and doing quite well with home made single beam camera triggers in cave entrances where bats have a very predictable flight path. But this just didn't cut it for more open situations and data gathering. What I needed was something far better. So I developed the prototype electronic harp trap. This device was extremely frustrating to develop and it took a lot of effort. But it means I can set it up on a flight path and have the camera photograph bats as they fly between the two posts - which is great when used in conjunction with the Echo Meter Touch 2 PRO (EMT2P) - I get a call recording as the photo is taken. Pair up the recordings on the computer with the photos and viola! I now have a reference call. This is great for species that can be identified in the field, but some species must still be handled; however this technique has reduced the need to catch bats by a significant margin. So two days ago I revisited a cave on public land at Buchan, Victoria. I had been into this cave many years earlier and seen large numbers of eastern Australian bentwing bats (Miniopterus orianae oceanensis) and eastern horseshoe bats (Rhinolophus megaphyllus). As I approached the cave I could smell the guano wafting out with the wind. As much as I love bats, it's not always very comfortable to observe them! The cave was up against a cliff and the entrance ran parallel to it. One side was formed by the cliff and the other was a sheer drop. The ample entrance soon became very tight. Just enough for me to fit in. I squeezed my way through and wriggled through the mud and poo into another cavern. It was full of bats - especially bent wings but there were a handful of horseshoe bats among them. It was too tight for me to safely bring my camera in, and I didn't want to disturb the bats any more than I absolutely had to - so I quickly backed out, wriggled through the mushy guano floor and out into the daylight. I was covered in guano and it didn't smell all too pleasant, so after a shower I returned with all of my equipment to do some data gathering. As the entrance was much taller than wide, I used the 50cm version of the electronic harp trap. Setting it to trigger only the flashes I put the camera on a tripod and controlled it with a shutter release cable - the idea is to hold the shutter open until a bat trips a sensor and triggers the flash. This method works very well, as the flashes respond virtually instantly and the camera is already taking the photo; it's already dark so overexposure isn't a problem. Connecting the camera to any kind of trigger means that you need to adjust for camera lag - which, depending on the brand of the camera can be difficult and unreliable. With the flashes all set to low power I started the Echo Meter Touch 2 PRO and waited.
It wasn't long before the first bat emerged. With a loud, high pitched whining call coming through the EMT2P, it could only be one thing - an eastern horseshoe bat. These bats often roost alone in caves, bunkers and road culverts and have the remarkable ability to detect insects sitting on leaves and pluck them off in flight! This explains their complex "horseshoe" shaped nose leaf and oversize ears, not to mention their strange call. Soon after, a stream of bent wings emerged out of the cave, most of them triggering the flashes as they passed through the beam, each also activating the EMT2P on the way past. The unstable dirt outside the cave meant there was little room to set up the camera for a side-on shot, but I tried anyway with a wide angle lens and managed passable (but not great) shots of a bent wing and a horseshoe bat. The other tricky part is figuring out where the bats will cross the beam on a vertical scale. It's fine if you're just after data. But if you're after a tightly cropped photo it will take lots of guesswork and although the sensor and flashes didn't miss, aiming the camera for a close up isn't too easy.
Back "in the office" I put the photos with the sonograms from the EMT2P on Photoshop to create these reference images with sonogram overlays: