Kirsty Dixon will change your tune about bats. “There are a lot of historical misconceptions about bats - people think that they’ll attack you, that they’re vicious, but that’s just not true,” she explains. “Usually I can take their weight and measurements and they’ll just sit there in my hand. When I release them…they’ll look around, get their echo-location buzzers going, and fly away. I think they’re wonderful.”
Kirsty is a PhD candidate at the University of Tasmania. She studies the bats of the Tasmanian Midlands.
Tiny bats in Tassie
The eight bat species in Tasmania are all forest dwelling – during the day they roost under bark and in old tree hollows. The largest species in Tasmania, the Eastern Falsistrelle, weighs up to 23g; the smallest, the Little Forest Bat, weighs only about 4g! All eight species are micro-bats that live on a diet of insects (mega-bats, like flying foxes, are fruit and nectar/pollen eating). As Kirsty explains, “The volume of insects that bats eat is astounding – insects that can be real crop pests and disease vectors. If the bats weren’t there, we’d be in a lot more trouble.”
This much we know. But we don’t know how bats survive in fragmented agricultural areas, like the Tasmania Midlands. What parts of the habitat do they use? Do they need big patches to thrive? How old or complex does a patch of vegetation need to be before the bats actually use it for foraging? And how can we make sure that we protect and revegetate areas with all of this in mind?
Sonograms of bat calls
How do you study such tiny, nocturnal bats? Kirsty sets up audio-recorders to record bat calls. Because bat calls are at frequencies beyond human hearing, you need ultrasonic monitors, known as bat detectors. Once the sound is recorded, Kirsty prints out sonograms – a sound picture of bat calls. Each bat species has a call with a distinctive shape and frequency range. After many months of field work, Kirsty has learnt to distinguish the different calls of the eight bat species.
Harp traps and bats
Kirsty then traps bats for call verification – to check that she is identifying the species correctly on the sonogram. She uses harp traps to capture bats. A harp trap looks like a square harp with two sets of slightly offset wires. Kirsty places the traps along ‘fly-ways’ – flight paths used by bats. Bats can detect the wires, but they have some difficulty flying through them. They drop, unharmed, into the catch bag, and they’re collected, identified, weighed and measured and then released again as soon as possible (usually within 15 minutes of being trapped).
This list of ultrasonic recordings becomes the ‘presence/absence’ data for each Midlands site: a list of which sites the bats are using and how often. Kirsty has deployed monitors in seven vegetation types: 1) sites replanted by Greening Australia, Bush Heritage, the Tasmanian Land Conservancy and/or landholders; 2) small, 3) medium and 4) large patches of native remnant vegetation; 5) open paddocks; 6) isolated paddock trees; and 7) pivot irrigation circles.
Restoring the Midlands
Kirsty’s research is one part of a large study based in the Midlands, which aims to investigate how species deal with the fragmentation of their habitat and other threatening processes such as feral predators. It’s a collaboration between the University of Tasmania, Greening Australia, Bush Heritage, the Tasmanian Land Conservancy and the state government and many committed landholders.
Kirsty has enjoyed working with landholders. As she says, “They’re all interested in what’s going on. They want to know what they can do to make the land better. Overall, I chose this project because I felt that it could have a lot of positive outcomes for a range of different stakeholder groups.”
To hear more about Kirsty’s research, listen to her interview on ABC Radio.
- Kate Cranney, Science Communicator Intern.