Common name: mahogany glider
Scientific name: Petaurus gracilis
Conservation status: This species is listed as Endangered in Queensland (Nature Conservation Act 1992) and is Endangered nationally (Environment Protection and Biodiversity Conservation Act 1999). It is ranked as a critical priority under the department's Back on Track species prioritisation framework.
The mahogany glider is a small gliding possum occurring in Queensland. It is nocturnal, elusive and silent for much of the time. It was described in 1883 from a skin by Charles de Vis, a noted naturalist and amateur geologist who became an early curator of the Queensland Museum. Little more was known about the mahogany glider for over a hundred years and doubts were raised at to whether it actually existed. However, some clever detective work by scientists resulted in the exciting rediscovery of the mahogany glider in 1989 at Barrett's Lagoon near Tully in north Queensland.
The mahogany glider receives its name from its buff-coloured belly. The top of the head is pale and bears a dark stripe. Fully grown mahogany gliders are around 600 mm long from head to tail-tip and weigh 300-450 g.
The mahogany glider, in common with other gliders, has two folds of skin which stretch between the front and rear legs. These act as a parachute enabling individuals to glide for distances averaging 30 m and sometimes longer. The long tail is used for stabilisation especially when coming in to land on tree trunks.
Mahogany gliders are much larger than their closest relative, the squirrel glider, with which they may be confused in the wild.
Habitat and distribution
Mahogany gliders are restricted to the coastal southern Wet Tropics region of northern Queensland. They live in a narrow and highly fragmented band of lowland sclerophyll forest extending around 140 km from Toomulla, north of Townsville, to Tully and up to 40 km inland. Most recorded sightings have been at altitudes below 120 m. The main canopy and sub-canopy trees are eucalypts, bloodwoods and paperbarks and less commonly swamp mahogany and turpentine with an open mid-stratum of smaller trees and shrubs (e.g. wattles, forest siris, golden parrot tree, black she-oak, pandanus) and a grassy ground stratum in which grass trees may be present. The mahogany glider requires a relatively open forest structure for efficient gliding and tends to avoid dense vegetation such as rainforest.
Life history and behaviour
The mahogany glider forages alone at night feeding on nectar, pollen and sap from over twenty different species of trees and shrubs. It also eats honeydew (a sweet sticky substance excreted by insects such as aphids), insects such as lerps and the arils of wattles (an aril is a protein-rich stringy structure which connect seeds to the pod). Nectar and pollen feeding gliders are known to provide an important ecosystem function as pollinators of tree species such as some eucalyptus and banksia.
Mahogany gliders use hollows in large eucalypts and bloodwoods as dens for sleeping and rearing their young. They den either alone or in pairs and can use up to 10 dens in a single season. Dens are lined with a thick mat of leaves.
Mahogany gliders appear to be socially monogamous. Individuals may den with their mate and actively mark and defend their home ranges by chasing out other individuals. Territories are around 20 ha in size.
Mahogany gliders first breed at around 12–18 months and wean their young after four–five months. They generally raise only one litter per breeding season. A litter usually consists of one or two young, usually born between April and October. After weaning, juveniles of both sexes appear to disperse from the parental home range.
Isolation of populations and decline in habitat quality are major ongoing threats to the mahogany glider. Other causes of mortality include entanglement in barbed wire fencing, road kills and possibly predation by cats. The rufous owl and masked owl are natural predators.
Past clearing for agriculture, grazing, forestry and human settlement has reduced the total area of remaining mahogany glider habitat to around 110,000 ha, less than 20 per cent of the total area considered to be present at time of European settlement. The present population has been estimated to comprise about 1,500 individuals. Lack of suitable habitat in which young animals can disperse may be a constraint on further expansion of the population.
The mahogany glider, being highly mobile, requires more or less continuous vegetation cover to range freely. Infrastructure corridors such as major roads, railway lines and powerlines present barriers to movement as do clearing and settlement patterns in the landscape. A population viability analysis suggests that a minimum of 8,000 ha of vegetation containing around 800 individuals is required for a localised population to remain viable. Presently, a number of large discrete patches of habitat survive.
Decline in habitat quality has been occurring through a combination of altered fire regimes (too much or too little), weed invasion and intensive grazing. Loss of habitat has been occurring in situations where sclerophyll forest is developing a rainforest understorey in the absence of fire. This trend is difficult to reverse using conventional management practices and has the potential to contribute to local extinction of mahogany gliders.
The mahogany glider's conservation and recovery involves a broad range of people. To date responses have included voluntary community actions and habitat protection provided by legislation and statutory mechanisms.
A recovery plan has been prepared for the mahogany glider under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999. The recovery plan contains a comprehensive list of recommendations that guide investment in recovery actions for the species. Examples of recovery actions include an updated habitat map and erection of launching poles to enable mahogany gliders to cross the Bruce Highway at Easter Creek neat Ingham. Launching poles and a rope bridge fauna crossing have been installed at Corduroy Creek in a collaborative project involving state and local government, landholders, road builders, Traditional Owners and the Tully Branch of the Wildlife Preservation Society of Queensland.
The launching poles are approximately 25 m high, with a rope bridge across the two tallest poles, and rope in a spiral down each pole to aid the gliders to get up and down. There are also cross arms on the poles so gliders can launch themselves into flight - or they can crawl across using the rope. Other arboreal animals, including sugar gliders and striped possums, could also use these poles and ropes to get across the road.
Research on mahogany glider crossing behaviour was conducted at Bambaroo Hills, about 40 km south of Ingham, in 2007, where gliders use existing power poles to cross. This study recorded 25 tracked crossings over the highway by one particular male. In contrast only one crossing was observed by a female in this same study period. Similar research is currently underway at Mullers Creek, with the University of Queensland (UQ) looking at crossing behaviour across the Powerlink easement, the Bruce Highway and the QR railway, where gliders currently use natural emergent trees to cross these gaps.
Around 45 per cent of surviving mahogany glider habitat is contained within lands managed by the department. Remnant vegetation that is mahogany glider habitat on other land tenures is protected from further loss through the Vegetation Management Act, 1999 and through the Far North Queensland Regional Plan 2009-2031 that is a statutory plan under the Planning Act, 2016.
The Far North Queensland Regional Plan 2009-2031 identifies “strategic rehabilitation areas”, critical landscape linkages that are presently cleared or heavily fragmented. The objective of identifying strategic rehabilitation areas is to guide where landholders and stakeholders can direct habitat restoration. Plantings in strategically important landscape linkages have already been undertaken using trees and shrubs grown through a nursery program at local primary schools.
Artificial den boxes have been installed at selected sites of fragmented habitat on freehold property and the department's estate within the Cardwell area with the support of landholders. These are known to be used by mahogany gliders when animals are dispersing. With barbed wire fences causing mahogany glider deaths and injuries, landholders are being encouraged to replace the top strand of barbed wire with plain wire. On average, two injured mahogany gliders require rehabilitation and care each year.
Response to Tropical Cyclone Yasi
In February 2011 Tropical Cyclone (TC) Yasi battered the north Queensland coast, causing severe damage to important mahogany glider habitat. The damage sustained was more significant and widespread than TC Larry in 2006. The worst affected areas were narrow wildlife corridors west of the Bruce Highway, between Meunga Creek and Euramo.
The department implemented a disaster response strategy for the mahogany gliders which included:
- Installing supplementary feed stations on freehold property, department managed areas and strategic wildlife corridors in partnership with Wildlife Preservation Society of Queensland, Girringun Rangers, the community and the RSPCA.
- Installation of den boxes to supplement the lost tree hollows.
- Students from James Cook University and World Learning - SIT Abroad assisting the department with research and monitoring activities associated with the impacts of TC Yasi on the species and its habitat.
- Developing and implementing a long term monitoring program to gain a better understanding of the Mahogany Glider population.
Prior to TC Yasi, four mahogany gliders were being tracked by the University of Queensland in the Mullers Creek area - two of them have been located following TC Yasi. One of the study's radio collared gliders, 'Bono', was observed east of the QR railway line, indicating that at least on one observed occasion this mahogany glider has crossed all three gaps (Powerlink easement, the Bruce Highway and the QR railway) since TC Yasi passed.
In early August 2011, two pouch young mahogany gliders were found by departmental officers during an inspection of the health of a den pair at a monitoring site just north of Cardwell. While officers are still unsure how this species will manage through this recovery period, the early signs are promising.
Further good news is that the glider poles at Corduroy Creek survived the force of TC Yasi and the forest is showing good signs of recovery with shoot and leaf growth, flowering and limited fruiting recorded. The forest recovery has a long way to go but some of the critical components of mahogany glider food are now naturally available.