| Greater glider[1] | |
|---|---|
_in_a_Eucalypt.jpg) | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Infraclass: | Marsupialia |
| Order: | Diprotodontia |
| Family: | Pseudocheiridae |
| Subfamily: | Hemibelideinae |
| Genus: | Petauroides Thomas, 1888 |
| Type species | |
| Didelphis volans Kerr, 1792 | |
| Species | |
 | |
| Greater glider range | |
| Synonyms | |
Schoinobates | |
Thegreater gliders are three species of large glidingmarsupials in the genusPetauroides, all of which are found in easternAustralia. Until 2020 they were considered to be one species,Petauroides volans. In 2020 morphological and genetic differences, obtained usingdiversity arrays technology, showed there were three species subsumed under this one name. The two new species were namedPetauroides armillatus andPetauroides minor.[2]
These species are not closely related to thePetaurus group of gliding marsupials but instead to theLemuroid ringtail possum,Hemibelideus lemuroides, with which it shares the subfamilyHemibelideinae.[1]
The greater gliders arenocturnal and are solitaryherbivores feeding almost exclusively onEucalyptus leaves and buds.[3] Like their relative, the lemur-like ringtail, the southern greater glider is found in two forms: a sooty brown form and a grey-to-white form.[3] The central greater glider is instead silvery brown, while the northern greater glider is brownish-gray.[2]
The greater gliders are found in eucalypt forests fromMossman, Queensland, toDaylesford, Victoria.[3]
Although the genus was formerly thought to bemonotypic, there are now known to be three species in the genus:[2][4]
The species are known tohybridize with one another near the edges of their ranges.[2]
The three species differ in their size, with the northern greater glider only growing to the size of a smallringtail possum, while the southern greater glider grows to the size of ahouse cat. The central greater glider is intermediate between these two.[5]
Greater gliders have a head and body 39 to 43 centimetres (15 to 17 in) long, with the females generally being larger than the males. Their body is covered with a shaggy coat of fur that increases their apparent size, and the tail is long and bushy, ranging from 44 to 53 centimetres (17 to 21 in). The head is short with a pointed muzzle and their large ears are fringed and backed with long fur.
Each side of the body bearsmembranes stretching between the elbow and the ankle that give these animals the ability to perform controlledglides. This is in contrast to other gliding marsupials, such as thesugar glider, that have gliding membranes stretching from the wrists to the ankles.[6]
The feet have strongly recurved claws to grip onto bark or other surfaces. There are five toes on each foot. The first toe on the hind foot and the first two toes on the fore foot are opposable.[6]
The fur is soft and up to 60 millimetres (2.4 in) long. All three species have cream undersides and primarily differ in the coloration of their pelages. Thenorthern greater glider has a brownish-gray coloration, thecentral greater glider has a dark silvery-brown coloration with dark brown face, legs, and tail, while thesouthern greater glider varies between a dark, almost black morph or a pale white and gray morph. Body mass varies from 1,600 grams (3.5 lb) in the southern greater glider ofVictoria to 600 grams (1.3 lb) in the northern greater glider of northQueensland.[2]
Heat management in the greater gliders is performed by licking extremities and theventral body surface, and directevaporation is the main method of cooling. They can also use their gliding membranes to reduce heat loss by increasing the layer of insulation at the skin surface. The gliders are not well equipped to handle high ambient temperatures as they inefficiently use water for evaporation viasalivation despitearboreal habitats often having limited water accessibility.[7]
These gliders can digest low nutrientfoliage, specificallyeucalypt leaf matter, which contains a variety ofphenolic andterpenoid compounds and a high concentration of lignified fibre. These animals can digest about 50–60% of the leaf during its passage through the gut.[8] Their guts have a specializedcaecum that contains a population of bacteria that ferment food residues that remain undigested in the small intestine.[9] For a population in aeucalypt forest nearMaryborough, Queensland, it has been calculated that their daily energy intake is about 1130 kJ, which is provided by about 45 to 50 grams (0.099 to 0.110 lb) of dry matter daily.[10]
Mature females will give birth to a single joey each year which is typically born in late autumn or early winter. The underdeveloped offspring will then spend the next four months within the pouch of the mother to suckle and develop, and will remain within the security of the pouch until nine months of age.[11]
Greater gliders are found in southernQueensland,[12] eastern Australia,[13] southeasternNew South Wales,[14] and the montane forests of theVictorian central highlands.[15] It is usually tracked via spotlighting on transects (considered to underestimate the actual population size), radio tagging and owl-call playback.[16][17]
The greater gliders choose habitat based on several factors, with the dominant factor being the presence of specific species of eucalypt. Distribution levels are higher in regions of montane forest containing manna gum (E. viminalis) and mountain gum (E. dalrympleana,E. obliqua). Furthermore, the presence ofE. cypellocarpa appears to improve the quality of habitat for the greater gliders in forests dominated byE. obliqua. Another factor determining population density is elevation. Optimal levels are 845 m above sea level.[18] Within a forest of suitable habitat, they prefer overstorey basal areas in old-growth tree stands.[16]
The greater gliders are primarilynocturnal, spending the nightforaging in the highest parts of the forest canopy. During the day, they spend most of their time denning in hollowed trees, with each animal inhabiting up to twenty different dens within its home range. The dens are often lined with leaves and strips of bark.[6][19] This is whyspotlighting has become a popular way of locating members of a population. When a strong light is directed at the eyes of a glider, the observer will see two bright red orbs reflecting back.[17]
Within forests, males and females will have home territories and set borders between other individuals. For males, home territory ranges from 1.4 to 4.1 hectares (3.5 to 10.1 acres) while that of females is only 1.3 to 3.0 hectares (3.2 to 7.4 acres). Although home ranges may overlap, the animals remain generally solitary outside of the breeding season, and only rarely interact. In large and small patches of forest, the home territories will respectively be larger and smaller.[20]
The gliding posture of the greater gliders is unique among marsupials. The forelimbs are folded so that the wrists are tucked under the chin, giving the patagium a triangular outline when outstretched. These animals regularly glide between high trees, and are able to use their tails to assist in steering. They avoid traveling along the ground whenever possible, and are slow and clumsy if forced to do so.[6]
Greater gliders do not make any loud sounds,[21] and are thought to communicate through scent marking. The animal'scloacal glands give it a generally musty smell.[22][23]
Greater gliders subsist almost entirely on the young leaves and flowerbuds of select eucalypt species, especiallyEucalyptus radiata,Eucalyptus viminalis, andEucalyptus acmenoides.[22] Young leaves are preferred because they have higher concentration ofprotein, and lower concentration oflignocellulose which provides no nutrition. Overall, eucalypt leaves are a poor source of nutrients.[24]
Due to its nocturnal lifestyle, a natural predator of the gliders is thePowerful Owl (Ninox strenua). It hunts by concentrating in pockets within their relatively large home range until populations of prey are depleted to a level that causes the owl to shift hunting grounds.[25] Other predators include feral cats, introduced to Australia with the arrival of Europeans.[26]
The breeding season for greater gliders is relatively brief, lasting from February to May, with births occurring between April and June. Females have a relatively well-developedpouch, opening towards the forward part of the animal, and containing twoteats.[6] Only a single young is born each year.[3]
At birth, the young weighs only around 0.27 grams (0.0095 oz), but it does not begin to leave the pouch for about four months, by which time it is already furred and well developed. After leaving the pouch, the mother may carry it about on her back until it is weaned at about seven months of age. The young are independent at nine months, and reach sexual maturity between 18 months and two years after birth.[6]
Greater gliders have been recorded living up to fifteen years.[27]
Although previously thought to be related to theother gliding possums, the greater glider genus,Petauroides, is now known to be most closely related to theringtail possums, and especially to thelemur-like ringtail possum, from which its ancestors diverged around 18 million years ago. In contrast, it diverged from the gliding possums much earlier, around 36 million years ago.[28] Fossils of greater gliders are known from the latePleistocene onwards, and show that the animal was once more widespread and inhabited other areas including parts ofSouth Australia.[6]
Greater gliders as a whole are listed as endangered nationally, in Queensland, New South Wales, the Australian Capital Territory and Victoria, under the EPBC Act, the Queensland Nature Conservation Act and Victorian Advisory List of Threatened Vertebrate Fauna.[29] Given the split into three species, and the uniquely threatened status of the southern species, this may need revision.[5]
