How effective is spotlighting for detecting the squirrel glider?

Abstract

Recent studies have questioned the reliability of spotlighting to detect certain species of arboreal marsupial or to provide an index of population size. This study assesses the reliability of transect spotlighting to detect the squirrel glider (Petaurus norfolcensis) by comparison with grid trapping. Trapping was conducted for 3–4 nights, approximately every second month during 2001. Spotlighting was conducted monthly along four transects through the grid. The two techniques combined showed that at least 7–11 gliders were present during most of 2001 in the spotlit area. Trapping detected 1–4 individuals per census within this area. Only one was detected during 4 of 6 census periods. Spotlighting detected 2–4 individuals during 9 of 12 census periods. We estimate that spotlighting surveys detected an average of 25% of the squirrel gliders present; trapping surveys detected an average of 21% of gliders. We conclude that spotlighting under suitable conditions by experienced personnel was equally effective as trapping in detecting and providing a population index of squirrel gliders at our site. The generality of this finding must be tested at other sites. A review of published studies involving transect spotlighting of arboreal marsupials found that most incorporated repeat traverses of transects to improve detection, and standardised abundance or density for comparing site categories. Thus, the conclusions of these studies should not be affected by recognition that spotlighting detects only a proportion of the actual population size of a given species. We recommend further studies to assess detection of arboreal marsupials by spotlighting surveys.