Eradication of feral goats Capra hircus from Kangaroo Island: estimating the probability of persistence from multiple lines of evidence

Ongoing support for an eradication program depends on clear information being provided to on-ground operational and managerial personnel and funding agencies about the performance of control effort. This paper describes the methods used to track the success of control activities during goat eradication on Kangaroo Island, Australia, from 2006 to 2017. A range of techniques were used during the program to monitor the goat population, including helicopter surveys, Judas goats, walking transects, camera trapping, scat count transects, and opportunistic community observations. A Bayesian catch-effort model contained within a Microsoft Excel spreadsheet enabled data from multiple monitoring techniques to be accommodated. The familiar spreadsheet format made it relatively easy for operational staff to add data and visualize the strength of individual or combined monitoring techniques to track population decline. This provided greater incentive to maintain accurate records of hunting and survey effort during the eradication program. Combined survey effort data indicated there was a 1% chance that feral goats remained extant at the beginning of 2017. This probability was reduced to 0.1% if in another 12 months no further feral goat activity was detected by hunting effort and landholder/manager monitoring.