Alan Newsome

Ecological costs of feral predator control : Foxes and rabbits

We used a predator removal experiment to examine the role of red fox (Vulpes vulpes) predation in suppressing rabbit (Oryctolagus cuniculus) population growth in Namadgi National Park in southeastern Australia. At 2 sites, fox abundance was reduced with a 1080 poisoning campaign maintained over 18 months. The responses of rabbit populations in these fox-reduced sites were compared to 2 other sites where fox populations remained intact. In the 2 removal sites, rabbit populations grew to 6.5 and 12.0 times their initial population size within 18 months. In the untreated sites, rabbit populations showed very small population increases over the same period. The experiment demonstrated that 1 introduced pest species suppressed the population growth of another pest species. As fox removal was initially planned to protect native fauna threatened by fox predation, the response of the rabbits represents a serious ecological cost of fox control.

The influence of predation risk on foraging behaviour of brushtail possums in Australian woodlands

The potential effects of predation risk on common brushtail possums were investigated in south-eastern Australian woodlands. Patterns of habitat use, foraging costs using giving-up density (GUD) experiments, and indices of body condition and reproductive success were examined at eight sites in two habitat types (eucalypt- or cypress-pine–dominated stands), within three areas of different red fox abundance (high, moderate and low fox density). In cypress-pine–dominated stands, possums travelled further on the ground, visited more feeding stations and had lower GUDs at feeders where foxes were removed than did possums in high-fox-density sites. In contrast, there was no effect of fox removal on the behaviour of possums in eucalypt-dominated stands. Fox removal also had no effect on indices of body condition and reproduction. Minor effects of microhabitat were detected with trackplot and GUD experiments, but, overall, the results suggest that habitat at the stand-level was more important. The non-lethal effects of foxes in different habitats may need to be taken into account when developing conservation strategies for native marsupials.

Home ranges of feral cats (Felis catus) in central-western New South Wales, Australia

Twenty-one feral cats were radio-tracked using direct sighting and triangulation techniques (amassing 730 location fixes) during winter in an agricultural landscape in central-western New South Wales. Factors affecting home-range size, home-range overlap and habitat use were assessed. Mean home-range size was 248 ha (s.e. = 34.9, n = 15 cats, 598 location fixes). Home-range size and habitat use were not influenced by sex or age of adult cats, prey abundance or time of day. However, cat weight significantly influenced range size, with heavier cats having larger ranges than smaller cats. Although the cats are apparently solitary, their home ranges overlapped considerably, particularly between young adults and old adult cats. Cats were active both by day and night and did not occupy permanent dens. Home ranges encompassed mixed habitat types that provided both shelter and prey. Open woodland and open forest were the main habitat types covered by home ranges, but within these areas cats showed a preference for grassland, where rabbits were more abundant. The results recorded in this study indicate that cat-control programs should concentrate in mixed habitat areas, where both shelter and food are available, and over widely dispersed areas. The absence of group living suggests that the effectiveness of virally vectored fertility or biological control agents would be limited.

Do Exotic Vertebrates Structure the Biota of Australia? An Experimental Test in New South Wales

From 1993 to 2001, we conducted a series of experiments in a mixed grassland–woodland system in central New South Wales (NSW) to quantify the interactions between red foxes and their prey and competitors. Foxes were removed from two areas around the perimeter of Lake Burrendong, and data were collected from these areas and a nearby untreated area before, during, and after the period of fox control. The arrival of rabbit hemorrhagic disease (RHD) in 1996 provided an opportunity to examine the interactive effects of controlling foxes and rabbits. In this landscape, typical of central NSW, (a) the fox population was not affected by a large reduction in the abundance of rabbits, or vice versa; (b) the cat population declined in areas where foxes were removed after the large RHD-induced reduction in rabbit numbers, but there was no consistent response to the removal of foxes; (c) the abundance of some macropod species increased in response only to the combined removal of rabbits and foxes; (d) there were no consistent changes in the abundances of bird species in response to the removal of either foxes or rabbits, but there were clear habitat differences in bird species richness; and (e) there was likely to be an increase in woody plant species after the large reduction in rabbit populations by RHD. We conclude that (a) long-term field experiments (more than 3 years) are required to quantify the indirect consequences of controlling foxes and rabbits, and (b) single manipulations, such as fox control or rabbit control, are not necessarily sufficient for the conservation of remnant woodland communities in southeastern Australia.