Effect of pasture availability on bait uptake by feral pigs in Australia's semi-arid rangelands

Factors that influence bait uptake by feral pigs will determine the efficacy of poisoning and trapping programmes for the control of pigs and have the potential to introduce bias to indices of pig abundance requiring bait consumption. In this study, the influence of pasture availability on uptake of bait trails consisting of soaked wheat by pigs in the semi-arid rangelands of north-western New South Wales was investigated. Percentage uptake of bait trails, pig density and pasture biomass were estimated for six sites along the Paroo River on six occasions: two each when pasture biomass was relatively high, moderate and low. The influence of pasture biomass on the relationship between percentage uptake of bait trails and pig density was examined by linear regression analysis. The analysis demonstrated that increasing pasture biomass significantly reduced the density of pigs corresponding to a given percentage uptake of bait trails, suggesting that, as pasture biomass increased, fewer pigs consumed bait trails and/or the number of bait hails each pig consumed declined. Assuming the former, the effect of increasing pasture biomass on the relationship between percentage uptake of bait trails and pig density indicated that, for every increase in pasture biomass of 100 kg ha(-1), the percentage of pigs consuming bait declined by about 10%. The implications of these results for pig control and bias associated with indices of pig abundance requiring bait consumption are discussed.