We evaluated the efficacy of spotlight surveys
and passive track surveys conducted along roads for assessing the relative
abundance of feral cats and dingoes in a semi-arid rangeland environment in
central Australia. Track surveys were more time-efficient than spotlight
surveys and offered higher precision. We cover a range of issues that need to
be considered when using track-based surveys to assess population change. We
also discuss the merits of other techniques used to monitor the abundance of
mammalian carnivores.
There is a paucity of data on the movement patterns of feral cats in Australia. Such data can be used to refine control strategies and improve track‐based methods of monitoring populations of feral cats. In this study the home ranges and movements of male feral cats were examined over 3.5 years in a semiarid woodland environment in central Australia. Two home range estimators were used in the examination: (i) minimum convex polygon (MCP); and (ii) fixed kernel. The most widely used method of estimating home range in feral cats is MCP, while the fixed kernel method can be used to identify core areas within a home range. On the basis of the MCP method, the long‐term home ranges of feral cats in central Australia were much larger than those recorded elsewhere (mean, 2210.5 ha). Twenty‐four hour home ranges were much smaller (mean, 249.7 ha) and feral cats periodically shifted their 24 h ranges within the bounds of their long‐term home ranges. Core area analysis indicated marked heterogeneity of space use by male feral cats. Several instances where feral cats moved large distances (up to 34 km) were recorded. These long distance movements may have been caused by nutritional stress. Using data from the literature, it is shown that prey availability is a primary determinant of long‐term home range size in feral cats. The relevance of the results to the design of management strategies for feral cats in central Australia is also discussed.
Context
Recovery of Australian rabbit populations from the impact of rabbit haemorrhagic disease virus (RHDV) contrasts with more prolonged suppression of wild rabbits in Europe, and has been widely discussed in the scientific community, but not yet documented in formal scientific literature. The underlying causes of recovery remain unclear, but resistance to RHDV infection has been reported in laboratory studies of wild-caught rabbits.
Aims
We document numerical changes in two South Australian wild rabbit populations that were initially suppressed by RHDV, and examine serological data to evaluate several alternative hypotheses for the cause of recovery.
Methods
Rabbit numbers were assessed from spotlight transect counts and dung mass transects between 1991 and 2011, and age and RHDV antibody sero-prevalence were estimated from rabbits shot in late summer.
Key results
Rabbit numbers were heavily suppressed by RHDV between 1995 and 2002, then increased 5- to 10-fold between 2003 and 2010. During the period of increase, annual RHDV infection rates remained stable or increased slightly, average age of rabbits remained stable and annual rainfall was below average.
Conclusions
Rabbit populations recovered but neither avoidance of RHDV infection, gradual accumulation of long-lived RHD-immune rabbits, nor high pasture productivity were contributing factors. This leaves increased annual survival from RHDV infection as the most likely cause of recovery.
Implications
Previously documented evidence of resistance to RHDV infection may be of little consequence to post-RHD recovery in rabbit numbers, unless the factors that influence the probability of infection also shape the course of infection and affect survival of infected rabbits.
Habitat use by feral cats and dingoes was examined within a heterogeneous semi‐arid woodland site in central Australia over 2 years. Density estimates of feral cats based on tracks were higher in mulga habitat than in open habitat. Isodar analysis implied that this pattern of habitat use by feral cats was consistent with the consumer‐resource model of density‐dependent habitat selection, which is an ideal free solution. The reason why mulga supported higher densities of feral cats was unclear. Foraging success of feral cats may be higher in the mulga because the stalk and ambush hunting tactics typically employed by felids are well suited to dense cover. Mulga may also have offered feral cats more protection from dingo predation. Dingo activity was distributed uniformly across habitats. The dingo isodar was statistically non‐significant, suggesting that habitat selection by dingoes was independent of density.
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