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ScienceWise - Nov/Dec 2009

Radio Mice & Poisonous Snakes

Article Illustration
The tracking on one day led to this diamond python - there goes mouse 6E4EA12. Photo by Christopher MacGregor
Article Illustration
The eastern chestnut mouse with collar attached. Photo by Wendy Hartman

The Hazardous Life of Australia’s Native Mice

How do you manage for an animal like the eastern chestnut mouse (Pseudomys gracilicaudatus)? It’s a small endangered native rodent found in heath along the east coast of Australia (and nowhere else in the world), but we know precious little about its basic biology and natural history. The species has a patchy distribution, maintains low population densities and is believed to be a fire specialist as its numbers usually peak in the years following wildfires. But very little else is known about its resource requirements.

Where does it shelter? What characterises its refuge habitat and are these sites limited in the landscape? How far does it move from day to day? What sort of social strategies and behaviours does it employ to maintain a viable population at low density? Without this basic information it’s almost impossible to effectively conserve the eastern chestnut mouse. Which is where Felicia Pereoglou from the Fenner School of Environment and Society steps in. For her PhD, Ms Pereoglou is capturing and tracking the little mouse down in the Booderee National Park at Jervis Bay on the NSW south coast. The species was recently re-discovered in the region, which now represents the southern distributional limit, and supports the most isolated population of the species found along the east coast of the continent.

“I’m currently completing a radio-telemetry study of the habitat requirements, daily movement and social behaviour of eastern chestnut mice,” explains Ms Pereoglou. “The information gained from this investigation will provide an understanding of the strategies this species uses to persist at low densities. Knowledge of the patterns of daily movement and how they vary between individual animals, sexes and across seasons provides important clues about population social structure and other aspects of a species’ biology. In conjunction with habitat/refuge site selection data, daily movement information has the potential to identify resources that may limit population densities of this threatened species.”

While the research is specifically aimed at learning how to better manage eastern chestnut mice, it also has important implications for other threatened species of native rodents that are rare and ‘patchy’ within their distribution, and/or specialise for ephemeral, fire-prone habitats.

While radio tracking small endangered mammals sounds fascinating, it’s no easy task. It’s a labour-intense research technique, and before you radio collar and track a subject you have to catch it.

“No-one should underestimate how much effort goes into trapping and then tracking these animals,” comments Ms Pereoglou. “First you have to carry between 100-200 aluminium traps (Elliot traps) out into the field, setting them out one every 10m over an area of 2-4 hectares and then bait them with a mix of rolled oats, peanut butter and fennel seeds. Then you have to monitor them.

“A proportion of the baited traps are inevitably triggered by birds or possums who eat the bait, while other traps are trampled by kangaroos. I also frequently catch species that are not necessarily wanted (such as red-bellied black snakes) or those that are unexpected but a pleasant surprise (such as the eastern pygmy possum).”

Captured eastern chestnut mice wear radio-transmitters as a collar attached with a cable tie, and Ms Pereoglou says each animal has its own personality.

“Some are easy to handle and some hate being handled and try and bite at any opportunity (sometime through the calico handling bag),” she says. “And some try and attack the radio-transmitter collar while it’s being attached. Once the collar is attached, the animal is released at the point of capture and tracking starts the following day.”

Radio tracking involves many hours of listening to beeps at various frequencies and intensities, as your radio receiver gives you directional signal. It enables you to identify where the collared mouse is to about a metre accuracy. Ms Pereoglou says it takes practice to become a good radio tracker and there are often situations where the unexpected happens, and the animal being tracked starts doing things that are out of the ordinary.

“You worry when the animal being tracked is doing something a bit odd,” says Ms Pereoglou. “But usually it doesn’t take too long to discover what’s happening. For example, one day when I was out tracking a female mouse early on a summer day the receiver was saying the animal was below me but when I changed the aerial to pinpoint the exact location the signal would disappear and move off slowly. That’s very un-mouse-like – they usually either sit still or run away fairly quickly and not necessarily quietly. In any event, I kept following this signal until about 50cm away in knee high thick heath vegetation I spotted a coil of a large eastern brown snake looped over a grass tree – there goes mouse 6E4D0F6!
“On a different occasion I felt sure another mouse had been eaten or had discarded its transmitter collar because it was moving around in an area that was atypical mouse country. I persisted and, with the assistance of two other researchers, we crawled through some very thick vegetation (full of ticks) to try and find the mouse and/or collar. As I was trying to confirm the direction of the best signal I looked up and saw a ringtail possum nest. One of the researchers looked inside and reported a diamond python was in there. The python slithered away and when the aerial was pointed directly at it, the signal became very strong. So we grabbed the python and there was a transmitter collar-shaped bulge inside its gut – there goes female 6E4EA12.”

Such is life when you’re radio tracking small mammals. Ms Pereoglou reported a range of other mishaps: a few other predation events, some shed collars, and a mouse caught in a vine.

“At least I can say it’s never dull,” she comments. “There’s lots of interesting information being discovered all the time – predator-prey interactions, predation rates, habitat selection, social interaction, nest sharing and daily movements.”
“And as each radio-tracking day takes off I’m sure I’m thinking the same thought that mice trackers have pondered before me: “I hope this time my mouse is near the track…”

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