Towards meaningful monitoring: A case study of a threatened rodent

Abstract

Detecting trends in species' distribution and abundance is essential for conserving threatened species, and depends upon effective monitoring programs. Despite this, monitoring programs are often designed without explicit consideration of their ability to deliver the information required by managers, such as their power to detect population changes. Here, we demonstrate the use of existing data to support the design of monitoring programs aimed at detecting declines in species occupancy. We used single–season occupancy models and baseline data to gain information on variables affecting the occupancy and detectability of the threatened brush-tailed rabbit-rat Conilurus penicillatus (Gould 1842) on the Tiwi Islands, Australia. This information was then used to estimate the survey effort required to achieve sufficient power to detect changes in occupancy of different magnitudes. We found that occupancy varied spatially, driven primarily by habitat (canopy height and cover, distance to water) and fire history across the landscape. Detectability varied strongly among seasons, and was three times higher in the late dry season (July–September), compared to the early dry (April–June). Evaluation of three monitoring scenarios showed that conducting surveys at times when detectability is highest can achieve a substantial improvement in the ability to detect declines, thus reducing the survey effort and costs. Our study highlights the need for careful consideration of survey design related to the ecology of a species, as it can lead to substantial cost savings and improved insight into species population change via monitoring.