The bilby (Macrotis lagotis) is listed as Vulnerable in Australia, is strictly nocturnal and shy, and it has proven difficult to estimate its population abundance. The aim of this study was to determine methodology that would reliably estimate the abundance of the bilby within an enclosure at Currawinya National Park, south-west Queensland. We estimated the abundance of bilbies on long-term monitoring plots by counting pellets comparing two methods: counting standing odorous pellets using distance sampling and counting newly deposited pellets (FAR). Pellet deposition rate and decay rate were also estimated to enable population estimation using distance sampling. The density of odorous (<14 days old) standing pellets and old pellets was highest in October 2011 and dropped dramatically when plots were revisited in March 2012 and July 2012. Counting standing pellets using distance sampling provided a rigorous estimate of abundance of bilbies at Currawinya. Bilby density and pellet deposition rates were too low for the FAR method to accurately or precisely estimate bilby density. A population crash within the enclosure following an invasion of feral cats was mirrored by a dramatic decrease in pellet density. Incorporating detectability into abundance estimation should be carefully considered for conservation purposes.

A traditional design-reliant estimate of abundance is calculated by multiplying a density estimate obtained from transects to reflect the size of the study area. This type of estimate tells nothing about the nature of a species’ distribution between the samples. In contrast, model-based inference can better estimate abundance by interpolating transect estimates over the study area with the aid of covariates. This study used density surface modelling (DSM) to predict spatial distribution of greater bilby (Macrotis lagotis) and rabbit (Oryctolagus cuniculus) pellets within a predator-proof enclosure at Currawinya National Park, south-west Queensland. Pellets and latrines were counted using distance sampling and plot sampling on 30 PPBio plots during 2012 and 2014. Pellets and latrines were not strongly associated with habitat features, reflecting the generalist nature of both species. Bilby pellets were found on 23 plots in 2012 and 5 plots in 2014. Rabbit pellets were present on 29 plots in 2012 and 16 plots during 2014. These substantial declines in pellet abundances coincided with invasion of the feral cat (Felis catus) into the enclosure. While DSM modelling can allow managers to make informed decisions about applying survey effort or management practices, it is not suited to all species or situations.