Variation in sap feeding and tree testing by yellow-bellied gliders and the potential for population monitoring

Tree sap is important in the diet of the yellow-bellied glider (Petaurus australis). I investigated the use of 66 trees in sap feeding by gliders at 32 sites (equating to 32 glider groups) in eight surveys over 2 years in the Shoalhaven region of New South Wales to evaluate the potential to use such trees in population monitoring. I estimated the probability of detecting two different types of glider incision made on the sap trees within 0–3 months of a survey: one representing bouts of sap feeding and the other representing the testing of the suitability of these trees for sap feeding. The probability of detecting each type of incision varied by season, being lowest in autumn and highest in spring (feeding: 0.30 ± 0.03 (s.e.) to 0.51 ± 0.04; testing: 0.40 ± 0.04 to 0.63 ± 0.03). I also investigated whether detection of any new incision differed between individual sap trees at a site. The probability of detection per survey was equivalent (0.76 ± 0.03) between trees and between years. The incisions accumulate over a year, so scoring any incisions made since a previous annual survey will increase this probability. New incisions were detected in each of the two sample years at all sites indicating short-term stability in home range occupancy and demonstrating a useful method of population monitoring.