Are nest boxes a viable conservation management strategy as supplementary habitat for greater gliders?

Southern greater gliders (Petauroides volans) and other arboreal mammals in Australia and worldwide face escalating threats from habitat loss, climate change and stochastic events. In particular, the decline of hollow-bearing trees poses a substantial threat to these arboreal mammals and other hollow-dependant species. Therefore, there is a growing focus on proactive and reactive measures to aid in the conservation of these species. Nest boxes have been implemented extensively as a conservation management strategy to counteract the widespread decline of old-growth forests. Although widely implemented, nest box programs often lack robust experimental design, and concerns have arisen regarding the thermal properties of the boxes being inadequate for the greater glider, a heat-susceptible species. This thesis aimed to investigate the effectiveness of nest boxes installed as a supplementary habitat for southern greater gliders and other arboreal mammals at Seven Mile Beach National Park (SMBNP), NSW.

34 nest boxes were installed and 16 tree hollows that were known to be used by greater gliders were monitored to investigate their use and determine their thermal properties. The activity patterns and use of the nest boxes and hollows were monitored via motion sensor cameras placed facing the entrance of the dens to allow for continuous monitoring. 53% of the nest boxes in this study remained unused. Five of the nest boxes were used by the target species, southern greater gliders, and 11 boxes were used by common brushtail possums (Trichosurus vulpecula). Common ringtail possums (Pseudocheirus peregrinus) and a sugar glider (Petaurus breviceps) also used two separate nest boxes. It took 6-months for a box to be first used by a greater glider, however, two boxes were occupied by brushtail possums within 20 hours. Den sharing between two greater gliders was observed in both nest boxes and the hollows, plus den swapping between two arboreal mammal species was observed in multiple nest boxes. A larger percentage of the photos taken from hollows depicted birds compared to the photos taken from nest boxes. Furthermore, it was observed on multiple occasions that birds would alter the entrances of the nest boxes and hollows, although they were ultimately never used as nests. One nest box was overrun by european honeybees (Apis mellifera), and an observation was recorded where the bees caused a greater glider to abandon a nest box.

All of the nest boxes used by greater gliders were in an area of known low abundance of the species. Logistic regression models were used to determine that if nest boxes were placed in areas with fewer natural tree hollows, there was a higher likelihood of use by greater gliders. Where the nest boxes were placed in a tree (height above ground, orientation within the tree, canopy cover, and DBH of the tree) did not alter the probability that a nest box was used by a greater glider. There was a strong peak in activity at the entrance of the nest boxes and hollows directly after sunset, with a less distinct peak as the gliders returned to the before sunrise. The average time of activity around the entrance of the nest boxes and hollows ranged between 42 min to 195 minutes after sunset and 107 to 222 minutes before sunrise, depending on the season.

Temperature data loggers were placed within the nest boxes and hollows to analyse the internal thermal environment. It was found that both nest boxes and hollows experienced internal temperatures above 30 °C, including when they were occupied by southern greater gliders. The results from linear mixed models used in this thesis demonstrated that the maximum internal temperatures of nest boxes were higher than hollows during hotter days and lower than hollows during cooler days. However, it was modelled that both nest boxes and hollows have a lower internal temperature than the external ambient temperature on hotter days. Data showed that the ambient external temperature had a greater effect on the internal ambient temperature of the nest boxes, with tree hollows having less fluctuation throughout the day. However, it was concluded that tree hollows took longer to decrease in temperature as compared to the nest boxes. It was found that the orientation of nest boxes and hollows in this thesis had a considerable effect on the internal temperature. For both the nest boxes and hollows, the westerly-facing dens had the greatest maximum internal temperatures. It was determined through logistic regression models that as the daily temperature increased, there was a higher probability that a southern greater glider would not return to the same den the following night. The results from models in this thesis also predicted that the ambient humidity had a lesser but significant influence on the use of nest boxes by greater gliders.

The key findings of this study indicate that nest boxes can provide a supplementary habitat for greater gliders in areas lacking high-quality tree hollows. However, it remains essential to preserve hollow-bearing trees, as greater gliders exhibit a preference for natural tree hollows when they are available. Moreover, should there be an increased reliance on nest boxes for greater gliders and other arboreal mammal conservation management in the future, further research is needed to improve the thermal properties of the boxes, especially as climate change becomes a growing concern.