Recovery plan for the brush-tailed rock-wallaby - Department of ...

Approved NSW Recovery Plan Brush-tailed rock-wallaby
Main (1961) and Main and Yadav (1972) investigated the difference in black-footed rockwallaby
(Petrogale lateralis) populations on a group of islands off Dampier on the north-western
coast of Western Australia. The original population on the fox-free Enderby Island was
estimated to be 1500 animals while Dolphin Island (of similar size to Enderby but with foxes and
feral cats present), had an estimated population of 50. After fox control on Dolphin Island, there
was an almost 30-fold increase in the density of rock-wallabies. Nearby Depuch Island was
surveyed in 1962 by the Western Australian Museum, and at that time many black-footed rockwallabies
were present, but there was much evidence of fox predation which had only recently
arrived on the island. Twenty years later, there was no trace of rock-wallabies on Depuch Island.
The long history of circumstantial evidence implicating the fox, combined with their own
suspicions of fox involvement in black-footed rock-wallaby decline, led Kinnear et al (1988 and
1998) to attempt to gain more evidence. Their work concluded that the fox was a significant
factor in the demise and decline of native mammals, but that rock-wallabies can recover even
under serious fox predation. The validity of these conclusions has been critiqued (e.g. by Hone
1994 and 1999). Debate over the conclusions drawn from this study shows the importance of
testable hypotheses, in this case, the need to monitor predator numbers as well as prey numbers
to be able to demonstrate the reasons behind measured population changes.
Hornsby (1982) has reported a juvenile wallaroo (Macropus robustus) falling prey to a fox.
Studies by Banks (1997) and Banks et al (2000) on foxes and predation on native mammals and
rabbits at Namadgi National Park have strongly indicated that juvenile mortality in eastern grey
kangaroos (M. giganteus) was caused by fox predation. These studies also suggest eastern grey
kangaroos alter their behaviour in response to threats from foxes. This is consistent with Kinnear
et al’s 1998 finding that predation pressure can alter habitat use and foraging behaviour in blackfooted
rock-wallabies.
Although foxes have been implicated in the decline of macropods in Western Australia, there is
limited documented evidence of the impact of foxes on the BTRW. There are differences
between the habitat of black-footed rock-wallabies in Western Australia and of the BTRW,
which could affect BTRW susceptibility to foxes. Black-footed rock wallabies live on wheat
plains and rocky outcrops, whereas BTRWs live in forests, on continuous ridgelines and in
precipitous gorges.
Foxes are reputedly more effective predators of rock-wallabies than dingos, actively hunting
them on cliffs (Rolls 1969 in Short 1982). Dunn (1984) speaks of the agility and climbing skill
of the fox, and its ability to enter into all but the most inaccessible rock-wallaby refuges. Bayne
(unpub.) observed foxes flushed into the open when on a BTRW-occupied cliff on three
occasions, and twice watched foxes covering every part of a BTRW-occupied cliff and
examining each ledge and cave (all these occasions were on gorge–rim cliff colonies). Bayne
also noted that on one occasion the fox successfully negotiated a short section of slab.
In contrast, there is no strong evidence for fox predation in northern NSW. Of 144 fox scats
collected in the vicinity of BTRW colonies in north-eastern NSW, none contained the remains of
a BTRW (Lunney et al 1996). In addition, of 342 scats of dog, dingo and fox examined, BTRW
was identified as a prey item in only 1% (Lunney et al 1996), despite the examinations being
conducted to coincide with periods of pouch emergence and juvenile dispersal, when predation
on the BTRW was expected to be most likely (Lunney et al 1996).
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