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

Abstract

Small 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. Na€ ıve occupancy within eucalypt forest was 0.42. The detection probability (using 5-day detection occasions) varied with season (from 0.17 AE 0.04 in autumn to 0.34 AE 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.

Diet of the Dingo in Subtropical Australian Forests: Are Small, Threatened Macropods at Risk?

“…Due to logistical constraints, it was not feasible to operate cameras year-round, so we deployed cameras in winter as it represented the best compromise in detectability for our two target species, the long-nosed potoroo and red-legged pademelon [88]. Detection probabilities for the black-striped wallaby are highest in spring and intermediate in winter [89]. The habitat types preferred by the black-striped wallaby were uncommon in our immediate survey area, so we expected few detections of this species and instead focused on maximising detections of the other two species.…”

“…Disparities in the occurrence of macropod species can mostly be attributed to differences in habitats between reserves. Some macropods found in the dingoes' Richmond Range diet, such as black-striped wallabies, red-necked wallabies, and rufous bettongs, require grassy, open forest habitats [89,103] and are, therefore, not present in the areas sampled within the Border Ranges where this forest type is absent. Swamp wallabies have a broader ecological tolerance and occur across a range of habitats yet were also absent from the dingoes' Border Ranges diet.…”

“…Although rare in the dingoes' diet, the species was absent from the camera trap images, so their threat of predation is unknown. Sampling bias existed in that whilst black-striped wallabies prefer low-elevation eucalypt forest [89], the tracks along which the scats were collected and the cameras were operated in Richmond Range mostly followed wet sclerophyll and rainforest ridgelines. However, some camera locations did survey areas occupied by the black-striped wallaby, and some scat collection areas were within a 2 km vicinity of habitats occupied by this species (dingoes travel an average of 2 km between feeding and defecation [73]).…”