Controlling feral goats by shooting from a helicopter with and without the assistance of ground-based spotters

Abstract

The success of aerial shooting to control feral goats in arid and semi-arid environments has lead to its widespread use in rugged and more densely vegetated terrain elsewhere in Australia. In this experiment, the method’s effectiveness with and without the aid of ground spotters to assist in locating goats was evaluated in such terrain in the Chandler River Gorge near Armidale, New South Wales. The abundance of goats was estimated by applying a correction factor (1.45) to indices of abundance made by ground survey. Ground observers monitored success during the cull. Overall, only 31% of an estimated 462 goats were culled, at an average cost of $61 per goat. In all, 50% of the goats were in herds never seen by the helicopter crew, while the remaining 19% were individuals that escaped (17% unseen from the air) from herds that were shot at. Inconsistent culling success, combined with marked differences in the behaviour of goats in different experimental blocks, suggested that variable prior exposure to aerial shooting had a significant and confounding effect on the experimental outcome. Where goats had no prior experience of aerial shooting, culling success was 40% without spotter assistance and 59% with spotter assistance. Where there had been a history of aerial shooting the ground observers reported a marked increase in evasive behaviour, and the cull was only 21% even with spotter assistance. These results show that aerial shooting is not as successful in this type of terrain as has been assumed and suggest that its repeated or exclusive use will result in declining effectiveness as goats learn to evade the helicopter.