Estimating the home ranges of sugar gliders (Petaurus breviceps) (Marsupialia: Petauridae), from grid-trapping and radiotelemetry

Abstract

In this study, we examined the number of captures and radio-locations of sugar gliders (Petaurus breviceps) necessary to give reasonable estimates of home ranges. Using home ranges determined by radiotelemetry (RTHR) as a standard, we compared nine methods of estimating trap home range (THR) from grid-based mark-recapture data. Correlation analysis was employed to determine which method of estimating THR most closely correlated with RTHRs. A minimum of 12 captures appears to be adequate for reasonable long-term THR estimates derived from the harmonic mean measure (HMM, 50% isopleth). When RTHRs were estimated by either the minimum convex polygon method (MCP) or the HMM (95% isopleth) from loci collected every 30min, a minimum of 36 radio-locations was adequate. Mean RTHR estimates for identical data sets were 53 775m*2 and 35 333m*2 calculated from the MCP and the HMM (95% isopleth) respectively. A number of methods for analysing grid-trapping data produced THR estimates that were significantly correlated with RTHR estimates. Correlations were highest when RTHRs were estimated with the HMM as opposed to the MCP. RTHR estimates derived from the MCP were most strongly correlated with THR estimates derived by the minimum area method, HMM (50% isopleth) and observed range circle (r*2>0.48). When RTHR estimates were derived from the HMM (95% isopleth), the same correlations were higher (r*2>0.88) and THRs estimated by the boundary-strip methods and the adjusted range circle were also highly correlated (r*2>0.65). The significance of the correlations suggests that reasonable short-term THR estimates may be obtained from small capture samples by these above-mentioned methods of calculation. The HMM appeared to exhibit the greatest overall utility, with both radio-tracking and grid-trapping data. The success of the HMM in describing home range appears to be in its ability to depict centres of activity. The technique is most appropriate for animals such as sugar gliders which use concentrated but patchily distributed food resources, and consequently display uneven patterns of use of space.