By Emma Randle
On the brink of winter, when days have cooled to a mild 20 degrees and nights are getting cold, Arid Recovery undertakes its annual cage trapping. Cage trapping is designed to capture medium-sized reintroduced animals, such as bilbies and bettongs. Annual cage trapping is completed in the Main Exclosure paddock, which is free of native and feral mammalian predators. Nothing in ecology is ever simple. In the past, exclusion of predators has enabled some herbivores to increase beyond the carrying capacity of the environment at Arid Recovery. When burrowing bettongs were overabundant, there was dramatic reduction in palatable plants, such as the Ruby Saltbush, on the reserve. The trapping survey allows us to derive population estimates for bettongs and other reintroduced species so we can keep track of these changes. We also collect data on condition, weight, sex and body measurements that build an understanding of the health of the animals.
In three groups, 120 cage traps were spread across the Main Exclosure. Each trap was set with a big bait ball of peanut butter and oats to lure the animals in, two hessian sacks to insulate the cage traps during the chilly nights, and a stubby holder. You may be questioning why stubby holders were in all of the traps. No, the animals of Arid Recovery don’t have a drinking problem. Rather than nursing a drink, these stubby holders nurse some of the smaller animals that go into the cage. During cold nights, small trapped animals are at risk of dying from the cold. With native rodents in a massive boom phase on the reserve at the moment, the chance of catching them in the cage traps was especially high this year. To mitigate the risk, Arid Recovery’s ecologist, Genevieve, suggested using stubby holders to provide insulated shelter for native mice. Having seen these used successfully by other organisations, we thought it was a worthy pursuit. These stubby holders were all generously donated by the community. In fact, they flooded in!
The 4:30am morning alarm for annual cage trapping is an early one, but it enables trapping to be completed soon after sunrise. This minimises the time nocturnal animals spend in daylight, which can be stressful. It also decreases predation risk upon release from diurnal species, such as brown falcons or wedge-tailed eagles. After the sun is up, animals that have been caught are released into burrows for their safety. Finding these burrows can be time-consuming. It is amazing how many digging animals are around, yet how hard it is to find burrows. The early mornings are offset by some beautiful sunrises and having the opportunity to interact with such marvellous animals.
A great mix of animals were caught, with each group having the opportunity to process burrowing bettongs (Bettongia lesueur), Shark Bay bandicoots (Perameles bougainville) and greater bilbies (Macrotis lagotis). In the stubby holders, we found multiple spinifex hopping mice (Notomys alexis) and plains mice (Pseudomys australis) curled up together. Plains mice and spinifex hopping mice often set off the trap with the collective weight of several individuals, with a record five hopping mice caught together in one trap. In total, 186 hopping mice and 60 plains mice were found in the traps.
A total of 111 individuals of reintroduced species were caught across four nights. Nineteen Shark Bay bandicoots, which were reintroduced in 2006, were captured. The Shark Bay bandicoot is nationally endangered with less than 3000 left in the wild. They feed on invertebrates and plant matter. Some Shark Bay bandicoots had missing tails as a result of fighting with one another – leaving them looking more like a guinea pig than the smallest bandicoot in the world.
At Arid Recovery since 2000, greater bilbies were prevalent in the traps with 39 individuals captured. The iconic animals went extinct in South Australia nearly 100 years ago and now only survive in fenced areas in the state. These animals are important ecosystem engineers, overturning soil while digging for food and burrows, facilitating the regeneration of native plants. Processing the greater bilbies provided the opportunity to look at their amazing features, such as their large well-veined ears and crested tail that transitions from black to white on the end. It was fascinating watching them move off after processing them, moving with a hop, skip and a jump, and then into a casual ‘walk’ away.
Burrowing bettongs are the most eager to go into cage traps. Fifty-three individuals were caught in this year’s survey. Their inquisitiveness leaves them vulnerable to predation by feral animals. Sometimes, when under threat, burrowing bettongs will eject their young from their pouch To prevent this, tape is put over the pouches with young in them as a precaution. The tape comes off easily some hours later once the mother and young are safe in a burrow. On the occasions where a pouch young is ejected in a trap, they can be safely manipulated back into the pouch before being taped in.
Overall, the cage trapping survey this year was a success! Small animals were kept comfortable and cosy thanks to the stubby holders. Bilby numbers remain strong and bettong numbers stable. It was a fantastic opportunity to assess the numbers and condition of the animals after a few years of great rainfall. Getting up close and personal with endangered animals that were once widespread across Australia is such an amazing experience. For me, the annual trapping starkly highlights the impact of feral animals in the environment, as the reintroduced animals thrive in safe havens.