Aerial baiting of feral pigs (Sus scrofa) for the control of exotic disease in the semi-arid rangelands of New South Wales

An experiment that held the density of feral pigs constant while varying th e effective density of aerially distributed baits was conducted at three si tes in north-western New South Wales. Meat baits, containing one of the bio markers iophenoxic acid, tetracycline or rhodamine B, were distributed at d ifferent intensities over each site, and a sample of pigs was shot from a h elicopter at each site to determine bait uptake. Serum and tissue samples t aken from each pig were analysed for the occurrence of the biomarkers; the proportions of pigs exhibiting biomarkers represented the proportions of th e feral pig populations that had consumed baits at different baiting intens ities (expressed as baits per unit of pig density). The maximum percentage of sampled pigs that had eaten baits varied from 31% to 72% across the three sites. Bait uptake was regressed against baiting i ntensity. For two of the trials, the quantity of bait hypothetically requir ed to eliminate a population of feral pigs was extrapolated to be 1577 bait s per unit of pig density, while for the third trial 1874 baits per unit of pig density would have been required. Bait-uptake by non-target animals wa s substantial, posing potential hazards to birds and reducing the availabil ity of baits to feral pigs. Most likely, seasonal conditions affected bait- uptake by feral pigs. We discuss the implications of these results for exot ic disease contingency planning.