Bait consumption, and the efficacy of 1080-treated grain, were determined for feral pigs (Sus scrofa) during the dry season in the Fitzroy River region of north-western Australia. There were an estimated 250 pigs on the study site (15 000-ha paddock with beef cattle) before poison-baiting, and group size and the basic biology of these pigs were similar to that found elsewhere in Australia. All animals at the study site were naive to the test baits. Fermented wheat with added blood and bone was an attractant for feral pigs but added fish oil was not. Wheat and malted barley were the 'preferred' baits. Lupins and pig pellets were consumed in lesser amounts, suggesting that they are less/not acceptable to some feral pigs. Consequently, the efficacy of 1080-treated wheat and malted barley was determined (n = 3 sites per treatment). Three independent measures of pig activity/abundance were used. The daily sighting index before and after poison-baiting suggested that pig numbers were decreased by at least 81-100% (mean 89%) regardless of which bait was used. The take of both 1080-bait and non-toxic fermented wheat added to each station generally ceased within 1-3 days, and little take occurred during the post-poisoning follow-up. Pig tracks decreased to zero within 1-3 days of poisoning on the two sites where track plots were established. However, due to the arrival of 'immigrant' pigs ~6 days after poisoning on two sites, and the need to close down a third site before poison-baiting could be completed, we believe the absolute efficacy was greater than the 89% overall reduction. Even though they had access to bait, there was no bait-take by non-target species, either native (toxic and non-toxic bait) or domestic (non-toxic bait). The 61 pig carcases found after poisoning were within 20-610 m of active bait stations (mean 232 m), and most were found in clustered groups. These findings are discussed with respect to the development of management strategies for reducing the impacts of feral pigs, and in terms of their potential implications for developing wildlife disease (exotic and endemic) contingency plans.

Summary1. Demographic changes in response to surgically imposed female sterility were monitored in 12 free-ranging rabbit populations in south-western Australia over a 4-year period. This was part of a research programme aimed at examining the potential for virally vectored immunocontraception to limit the abundance of rabbits (e.g. using a recombinant myxoma virus) and other mammalian pests. Sterility levels were 0%, 40%, 60% and 80% of all females in year 1, with a similar proportion of female recruits sterilized surgically in subsequent years.2. There was a signi®cant decrease in rabbit productivity with increasing sterility level. This was overcome by increased survival of kittens and adults on the highsterility sites, such that the base-level numbers of rabbits were maintained, and mean annual rates of increase (r) were near zero for all treatments in all years. However, in the high-sterility populations this compensation was insucient to overcome the eects of sterility totally, and there was a marked decrease in the seasonal peaks in rabbit abundance for these treatments. 3. Survival and recruitment were dependent upon the level of sterility, and consequently the density of rabbits, with greatest survival of adult rabbits occurring on the 80% sites. Survival of sterile females was greater than that of other adults, probably because of their increased ability to maintain body condition during times of low pasture biomass (summer drought). Thus two density-dependent processes were identi®ed: the ®rst was operating through increased survival of juvenile rabbits, the second through increased adult survival, particularly sterilized females. 4. Because the proportional impact of immigration was greater (i.e. immigrants constituted a greater proportion of the population) and emigration was less, from the 80% sites, the eects of sterility may have been underestimated on these sites. 5. The abundance of European rabbit¯eas, a vector of myxomatosis, was signi®-cantly lower on the 80% sites, but this did not appear to aect the transmission of myxoma. Myxomatosis occurred as an annual epizootic in three of four years, with > 90% of rabbits on site after each epizootic testing positive for myxoma antibodies. 6. To achieve a sustained long-term reduction in rabbit abundance, 60±80% of female rabbits would need to be prevented from breeding. This could be achieved by a recombinant strain of myxoma provided the strain retained good transmissibility and all infected rabbits became sterile for life.

Demographic changes in three free-ranging rabbit (Oryctolagus cuniculus) populations were monitored over 4 years in southern Western Australia. Peak densities followed periods of high rainfall and pasture biomass. The breeding season was prolonged, often extending from at least April to November, with some pregnancies occurring outside this period. Fecundity, determined by the autopsy of pregnant offsite rabbits and the known length of each breeding season, appeared to be relatively high, with the potential for 34–39 kittens doe-1 year-1; however, because not all females are pregnant in all months, the overall productivity of these populations was estimated at 25–30 kittens adult female-1 year-1. Exponential rates of increase varied from 0.13 to 0.30 during the breeding periods and –0.05 to –0.14 during the nonbreeding season. Kitten survival was generally low whereas some adults lived for more than 5 years. Two patterns of myxomatosis were observed: annual epizootics of the disease (3 of 4 years) and an epidemic that slowly spread over many months. European rabbit fleas were most abundant during winter–spring and attained highest densities on adult female rabbits.

No abstract

Summary1. Toxicant-resistance is a potential, or very real, problem with many pest-control programmes world-wide. However, apart from rodents, pesticide-resistance has not been well documented in vertebrates. We assessed the potential impact of developing resistance to 1080 in rabbit populations with differing levels of historical exposure to 1080-baiting programmes in south-western Australia. 2. The sensitivity to 1080 of three out of the four populations of rabbits Oryctolagus cuniculus examined had decreased significantly since Australian rabbits were last tested over 25 years ago. The lethal dose 50 (LD 50 ) values for these populations, as determined from formal toxicity trials, ranged from 0·744 to 1·019 mg pure 1080 kg − 1 , and were significantly greater ( P < 0·05) than the previously reported values for Australian rabbits (LD 50 range 0·34-0·46 mg pure 1080 kg). The LD 50 value for the fourth population (0·584 mg pure 1080 kg − 1 ), which has had the least exposure to 1080, did not differ from that reported previously ( P > 0·05). 3. The lethal dose 99 (LD 99 ) values for the four rabbit populations tested ranged from 1·181 to 1·666 mg pure 1080 kg − 1 , and suggested that, theoretically, all rabbits should be killed during routine baiting campaigns provided that there is no loss of active ingredient from the bait. In reality, the efficacy of 1080 poison bait laid in trails for controlling free-ranging rabbits was reduced in those populations where rabbits had decreased sensitivity to 1080. Mean reductions in rabbit numbers 7-9 days after trail baiting of resistant and sensitive populations ranged from 51·2% to 65·2%, and from 76·4% to 76·5%, respectively. 4. These findings suggest that genetic resistance to 1080 is developing in at least some populations of Australian rabbits. This has world-wide implications for agricultural protection and wildlife conservation programmes that rely on a 1080-baiting strategy for reducing the impact of vertebrate pests.