Utilising power analyses and occupancy modelling to inform population monitoring of the regionally endangered black‐striped wallaby (Macropus dorsalis) in New South Wales

Abstract

AbstractSmall macropodoid marsupials are well represented among Australia’s extinct and threatened mammals. Population monitoring is central to understanding how remaining species respond to on‐going landscape change and threatening processes on private land and within managed conservation reserves. Camera trapping and occupancy modelling provide a reliable approach to monitor these often cryptic species. However, understanding the survey effort required to detect population declines of a given magnitude with high statistical certainty is often overlooked. We use empirical data from camera trapping and occupancy modelling to determine an optimal survey design for a regionally endangered population of the black‐striped wallaby. We established a 1200 ha grid of 60 cameras and sampled in three 30‐day intervals over a 1‐year period. We investigated factors that may influence occupancy and detection followed by power analyses with our broad objective being to devise a monitoring program that would be robust enough to detect a 50% decline with at least 80% power. This species was not detected at rainforest sites. Naïve occupancy within eucalypt forest was 0.42. The detection probability (using 5‐day detection occasions) varied with season (from 0.17 ± 0.04 in autumn to 0.34 ± 0.05 in spring). Occupancy was negatively influenced by shrub cover and negatively influenced by elevation. We found no apparent influence of dingo detection on occupancy or detection of the black‐striped wallaby. We explored different configurations of detection sites and number of survey occasions to satisfy our 50:80 criteria when initial occupancy was 0.40. Sampling 60 sites for a minimum of 30 days would satisfy these criteria. Power analyses can inform optimal designs for threatened species monitoring and similar investigations should be conducted for other threatened small macropods to assist their conservation.