A repeated soft hiss attracts my attention as I walk through the twilight of Seven Hills Nature Reserve. I retrace my steps and a furry tail whisks past me up an acacia tree. A juvenile Brushtail possum perhaps?
But then I see more small bodies climbing amongst the canopy and then a silent flight guided by expert eyesight and tiny membranous flaps of skin which stretch between front and hind limbs – is it a bird? is it a plane? No it’s a squirrel glider!
What a delight to stumble upon a feeding family of these marvellous creatures! And in a park less than five kilometres from the city and consisting of 52 hectares, these gliders are a marvel for the resilience of ecosystems despite a burgeoning human population and habitat destruction. They leap, glide and alight amongst the tallest trees with such grace – I see them making small incisions to suck at nutrient rich acacia sap, and I am transfixed for at least 30 minutes!
I contemplate later when I am back at home whether the seven hills nature reserve is a large enough habitat island to support these gliders into the future or will they succumb to well-known phenomenon in ecology called ‘ecosystem decay’?
A sombre thought in light of such a lovely discovery, but nonetheless a necessary one if we are serious about the protection of our wonderful flora and fauna. Ecosystem decay was a term first coined in the 1980s by Thomas Lovejoy1,2 and hypothesises that the fragmentation of once continuous habitats causes the gradual loss of species from a remnant habitat until a final stable number of species remains 1,2. This occurs due to complex array of factors including loss of genetic diversity due to inbreeding, a loss of available resources (shelter, food, etc) resulting in increased competition and edge effects 1.
Gliders require a continuous canopy to glide from tree to tree and allow dispersal while avoiding predation. They also require suitable old-growth trees with intact hollows for nesting, not to mention sufficient available food sources 3. Studies show they are not able to utilise highly modified landscapes such as farms or urban landscapes to visit distant populations in neighbouring bushland fragments 3. However, on a positive note their minimum home range is small being a maximum average 2.84 hectares, indicating that squirrel gliders may be able to survive in smaller habitat fragments such as the seven hills bushland reserve 1,3. I can only hope that due to the small size of squirrel gliders and their documented small home range requirements that several family groups may exist at seven hills. This should allow individuals living here to reproduce with other individuals which are not closely related, thus retaining their genetic viability and allowing them to remain at seven hills nature reserve both now and in the future.
Perhaps a genetic and home range study of sugar gliders in urban forests of Brisbane could be the topic for a future PhD or research project!
1 Laurance, W. F. et al. Ecosystem decay of Amazonian forest fragments: a 22‐year investigation. Conservation Biology 16, 605-618 (2002).
2 Lovejoy, T. E. et al. Ecosystem decay of Amazon forest remnants. Extinctions. University of Chicago Press, Chicago 111, 295-325 (1984).
3 van der Ree, R. The population ecology of the squirrel glider (Petaurus norfolcensis) within a network of remnant linear habitats. Wildlife Research 29, 329-340 (2002).