AERIAL SURVEY METHODOLOGY AND THE COST OF CONTROL FOR FERAL GOATS IN WESTERN QUEENSLAND

Feral goats (Capra hircus) were shot from a helicopter on four sites i n central-western Queensland. These sites centred on Idalia National P ark (660 km(2)) and three nearby properties: Lissoy (360 km(2)), Mt Ca lder (260 km(2)) and Ravensbourne (320 km(2)), the order reflecting in creasing goat density. On Idalia, 134 goats were shot in 8 h of flying time. On Lissoy, 28 goats were shot in 3 h, 1038 goats were shot on M t Calder in 15 h, while 2307 goats were shot on Ravensbourne in 21 h. The reduction was monitored by aerial surveys using fixed-wing aircraf t. No goats were recorded on either Idalia or Lissoy immediately follo wing shooting and substantial reductions in goat numbers were achieved on Mt Calder (75%) and Ravensbourne (49%). Surveys conducted six mont hs after this reduction indicated population increases on all sites fo llowing shooting. This was particularly marked on Ravensbourne, where goat numbers had increased by 31% despite further substantial removals by commercial mustering. These population increases were largely the result of immigration. The cooperation of landowners over a large area is therefore essential for effective control of goats. The per capita cost of shooting goats from a helicopter was essentially constant dow n to a threshold density of <1 goat km(-2), below which the cost incre ased substantially. The accuracy of fixed-wing aerial surveys was impr oved by using double-counting and these corrected estimates compared f avourably with index-manipulation-index estimates. Estimates of densit ies ii goat km(-2) were imprecise and at these densities goats were di fficult to detect. The extent of vegetation cover did not affect the s ightability of goats, whereas group size was positively correlated wit h the sightability of goats. To estimate true density, correction fact ors of 1-2 were applied to goat group sizes using survey parameters of 100 m strip width, a survey height of 76 m and a speed of 187 km h(-1 ).