Tracking Bettongs

Tracking populations of endangered Boodies, Woylies and Mala

Woylies (Brush-tailed Bettongs) and Boodies (Burrowing Bettongs) once numbered in their millions across southern Australia, before being driven to the brink of extinction by feral predators and habitat loss. Both species were declared extinct in NSW prior to their return to the wild at Scotia.

In order to estimate the population size of both species in Scotia’s Stage 1 area (4,000 hectares), AWC has set out a permanent grid of over three hundred cage traps. At sunset during the trapping period, these are baited with delectable balls of peanut butter, rolled oats and honey. After midnight on three consecutive nights, the ecology team returns to these traps to see what they’ve captured and to take all of the necessary measurements (weight, length, genetic samples etc). This gruelling but highly rewarding task usually takes until sunrise.

Boodies and Woylies appear to love the traps (or at least the peanut butter and rolled oats used in the bait). Nearly every Boodie or Woylie in Stage 1 is likely to be trapped during each monitoring session, providing a relatively accurate estimate of their population size. The graph below shows the population estimates of these two species since their reintroduction in 2005, when 170 Woylies and120 Boodies were released. The Woylie population then declined to around 30, where it has stayed ever since. Conversely, the Boodie population has gone from strength to strength with almost 300 now estimated to occur in Stage 1.

Why did the Boodies increase while the Woylies initially decreased? It is likely that the habitat at Scotia suits Boodies more than Woylies, such that the carrying capacity for Woylies in Stage 1, where Boodies are present, is around 30 and successful breeding and recruitment will only occur in years of above average rainfall. (Scotia has had below average rainfall for the past decade). The original distribution of these species supports this hypothesis: Boodies were found throughout the arid central deserts, whereas Woylies had a more semi-arid and temperate distribution. Boodies are better adapted to drier conditions, being able to avoid the heat of the day by resting in their burrows, whereas the Woylie rests up above ground in the shade.

Given the apparent competitive advantage of Boodies, we have released only Woylies in Stage 2, with 57 animals reintroduced last year. In the absence of competition with Boodies, the Woylie population has already increased slightly.

The overall stability of Scotia’s Woylie population is important given the species has declined precipitously during the past two years at the few remaining populations in south-western  Australia (except at AWC’s Karakamia and Yookamurra Sanctuaries, where the populations remain high and stable).

Why are Woylies ‘doing better’ at AWC sanctuaries? The answer is probably that most significant threats to Woylies have been removed at the AWC sanctuaries - the Woylie populations occur in feral-free areas, surrounded by feral-proof fences – ie, we provide complete protection from cats, foxes and the competitive impacts of rabbits and goats.

AWC has also begun reintroducing animals to Scotia’s Stage 2 fenced enclosure, which was declared feral-free in early 2008 and provides an additional 4000 ha of safety for native fauna.  In mid-2008, 57 Woylies were flown in from Karakamia and, after a month in quarantine, were released into Stage 2.  This population suffered an initial decline as they had to contend with a new, more arid environment.  More recently they appear to be on the increase, so much so that we no longer see the need to supplement the population in Stage 2.

Scotia also houses an ‘insurance’ population of Mala.  Mala are listed as extinct in the wild on the mainland, and only two other semi-captive populations exist.  At Scotia, our trapping revealed we housed almost 40 mala in the 100 ha mala enclosure in Stage I illustrating a doubling of the population since they were reintroduced.

Population estimates for Boodies and Woylies since their reintroduction in 2005.

Act Now

Please help AWC’s project to secure the future of six of Australia’s most endangered mammals, including the Bilby, the Woylie, the Bridled Nailtail Wallaby, the Boodie, the Numbat and the Stick-nest Rat which find refuge at Scotia.