Dr Jonathon Howard, NPA Executive
Arboreal mammals are important components of healthy ecosystems. The Southern Greater Glider (Petauroides volans), is a species of large gliding marsupial native to the forests of southeastern Australia. It is listed as endangered under the EPBC Act in Australia. Greater Gliders are the largest gliding mammal in the world. They are nocturnal and are solitary, feeding almost exclusively on eucalypt leaves and buds.
Wildfires are an important ecological disturbance, shaping landscape structure, species distributions, and habitat availability in eucalypt forest. However, extreme megafires -which have become a more recent phenomenon due to climate change and human activity- have unknown impacts. Studies so far have found that extreme megafires in Australia amplify both the positive and negative effects of a normal fire regime: it significantly alters the availability and quality of wildlife habitat, affects animal behaviours, makes some fauna more prone to predation, as well as affects how wildlife moves and uses different habitats.
The presence of arboreal mammals is strongly influenced by the availability of the key habitat components they depend on, particularly food and shelter trees. Studies have shown arboreal mammals are highly sensitive to forest disturbance such as fire. But our rapid departure from historical fire regime to a new phenomenon of megafires is of concern. It makes understanding how gliders respond and adapt to altered fire regimes key knowledge we must obtain to secure their future conservation and management.
Recent studies in behaviour in a post-fire landscape
Recently, researchers from the University of Sydney released their findings into how gliders cope with the effects of megafires. They captured and fitted GPS collars to 15 greater gliders in the forest region that was partially burnt in the 2019-2020 megafires; eight gliders lived in burnt forests and seven in unburnt forests. They collected 4,792 GPS points from the 15 animals tracked across these burnt and unburnt sites. On average, each collar recorded 12 fixes per individual per night.
They found the average home range size was 2.06 ha, but varied widely among the individual greater gliders, ranging from 0.70 to 4.88 ha. On average, individuals in burnt areas had larger home ranges (2.25 ha) than those in unburnt areas (1.84 ha), but this was not statistically significant.
Greater gliders in burnt forest had higher nightly and hourly movement rates than gliders in unburnt forest. They also exhibited more direct movements throughout the night. So, it seems that greater gliders have higher movement rates and more direct linear paths in burnt forests. Gliders are known to have home range fidelity. This may constrain the ability of animals to relocate following disturbance events like mega fires, and the results suggest that greater gliders simply adjust their behaviour in an effort to meet resource requirements rather than ‘move house’.
A key research finding being: Greater gliders remain loyal to their home ranges despite the severe disturbance caused by fire. In burnt forests, gliders travel farther within their home ranges and move in straighter paths compared to those in unburnt forests. Gliders adjust their movements to find resources in challenging conditions, and are able to show a degree of behavioural flexibility.
Activity patterns and post-foraging naps
The study also found greater glider activity was higher at the start and end of the night, with reduced movement through the middle of the night. Greater gliders are considered to be near the minimum size able to sustain a strictly folivorous diet. Due to their folivorous diet, this activity pattern is explained by the need for greater gliders to remain stationary for extended durations to aid digestion and conserve energy. Similar to the koala, low fermentation rates of eucalypt leaves, coupled with their small stomach size, restricts a glider’s food consumption and the energy they can derive from food.
The implications of this last finding are important because it suggest gliders have a limited foraging window, which may be particularly challenging in fire-affected forest if individuals spend foraging time navigating suboptimal habitat in search of food. That is, given a glider’s dietary limitations, drastic landscape changes -such as those resulting from megafires that influence forage availability and increase movement rates- could be detrimental for greater glider populations. It indirectly suggests that the presence of protected areas can reduce the biodiversity impacts when fire events or logging is disturbing habitat within a home range. Similar species exhibiting fixed behavioural strategies, like home range fidelity, will likely be challenged by severe and frequent habitat disturbance.
Protection of viable habitat will be crucial for the long-term sustainability of greater glider populations and, by extension, the overall health of eastern Australian forest ecosystems.