(Petauridae)
Class: Mammalia
Order: Diprotodontia
Family: Petauridae
Thumbnail description
Medium-sized, squirrel-like, active possums, all with marked dorsal facial stripes, four rounded cusps per molar
Size
1–2.5 ft (320–780 mm); 3.3–25.3 oz (95–720g)
Number of genera, species
3 genera; 12 species
Habitat
Open forest, woodland, closed forest, and rainforest
Conservation status
Endangered: 3 species; Vulnerable: 4 species; Data Deficient: 1 species
Distribution
New Guinea, Australia, including Tasmania
Evolution and systematics
Petaurids are the closest living relatives of pseudocheirids, based on cranial morphology, serology, and microcomplement fixation. Both families together are placed into a superfamily Pseudocheiroidea. There are some late Oligocene to middle Miocene and some early Pliocene records of species most likely belonging to Petaurus. Petauridae is subdivided into two subfamilies, Petaurinae and Dactylopsilinae, the latter being restricted to tropical northern Australia and New Guinea. The subfamily distinction is again based primarily on serology.
Physical characteristics
Aside from their distinct facial and dorsal stripes and the bunodent molars (four low, rounded cusps per molar crown), the two subfamilies are quite different in appearance. Petauridae are between 12.5 and 30.7 in (320 and 780 mm) long, weigh 3.3–25.3 oz (95–720 g), and are gray, brown, or cream-colored. They possess distinct frontal and sternal glands, particularly the males. All species of Petaurus are characterized by the gliding membrane, spanning from wrist to ankle, and a bushy tail, primarily used for steering in flight, but with a slightly prehensile tip. Dactylopsilinae are black and white with a very prominent longitudinal stripe pattern. Their fourth fingers are more or less elongated, and they have a very strong, almost skunk-like body odor.
Distribution
Dactylopsilinae are found in New Guinea, and one species occurs in the rainforest areas of northeastern Australia. The absolute lack of any fossil records suggests a recent immigration from New Guinea to Australia. Petaurinae are more widely distributed from New Guinea, through northern and eastern Australia to Tasmania.
Habitat
All species are arboreal, living in anything from open woodland to closed rainforests. They are nocturnal, spending the days in nests, normally in tree hollows. They are active climbers, running up and down thick tree trunks (also descending head first) as well as along horizontal or inclined branches and boughs. P. breviceps, as found in both field and laboratory studies, regularly experience daily torpor in winter, usually after several days of food withdrawal or restriction. Body temperatures drop to about 50°F (10°C) in these periods.
Behavior
Social organization markedly differs between the subfamilies. Dactylopsilinae are solitary (though no detailed field study has yet been conducted). There are some observations of vicious fighting between males over an estrous female, and the strong odor, as well as the loud, raucous calling during copulation, suggests a possible territoriality. Petaurinae all live in family groups of different sizes, with several adults of both sexes often sharing one nest. The larger species, particularly Petaurus australis, are described as monogamous or polygynous, and the smaller ones as polygynous. Hierarchies were found in P. breviceps, both for males and females. Subordinate females are harassed by the dominant one, and often lose their young during the first weeks after birth. Males often form codominance relationships with a brother or son, both being reproductively active. Dominant males perform paternal care such as baby-sitting, huddling, and grooming the young while the female is out of the nest. Home-range sizes vary between 1.2 acres (0.5 ha) (some P. breviceps) and 210 acres (85 ha) (P. australis). In P. australis there seems to be exclusive use and active defense, thus justifying the term territory. All species of Petaurus regularly use vocalization; P. australis utters loud, long-ranging calls that most likely serve as territorial advertising. All species use a variety of odors that seem to serve as nest and group odors, which emit from pedal, gular, frontal, sternal, and other glands. Feeding sites of Petaurus groups are defended against intruders. In P. breviceps, there is evidence for male philopatry and female (forced) dispersal. Not much is known about social dynamics in other species. Leadbeater's possum also lives in family groups, and seems to be territorial, which might be related to its feeding behavior.
Feeding ecology and diet
Dactylopsila is insectivorous, using its strong incisors as chisels to pry insects such as beetle larvae from their hollows in trees, or extracting them with their long fourth finger. The latter is also used in a tapping movement to detect hollows of larvae under the bark or in dead wood. Petaurinae are omnivorous, but with a heavy emphasis on sap feeding, nectar, and blossoms. All species of Petaurus are able to bite wounds into tree trunks to start sap flow, whereas Gymnobelideus is reportedly unable to actively prepare feeding sites. This is discussed as a reason for Gymnobelideus defending a territory and for Petaurus only defending feeding trees. Apart from sap feeding, nectar and pollen are important parts of Petaurus diet, while several species are known to be pollinators.
Reproductive biology
Apart from some anecdotal observations on copulation, which takes place on branches and is reported to be accompanied by loud screeches and calls similar to domestic cats, there is nothing known about Dactylopsila. Two young are born, and there are two teats in the pouch. In New Guinea, pouch young were found in January and October, while in Australia, reproduction takes place from February to August. Young are carried on the females' back once they leave the pouch. Petaurus young are also carried on the females' back after leaving the nest. The largest species (P. australis) is usually monogamous and carries only one young once per year, while the other species have one to two young once or twice per year, with births taking place April to September (as far as records from field data are available). In P. australis and P. breviceps, parental care is also provided by the resident male(s). Gestation in P. breviceps is 16 days, and the young remain in the pouch for 60 days. They first leave the nest at an age of 110 days, and are weaned at 110–120 days. Smaller species are typically polygynous.
Conservation status
Several species are currently regarded as not threatened as a result of their widespread distribution. Three species are listed as Endangered: Dactylopsila tatei lives on Fergusson Island and possibly on Goodenough Island, a small island west of New Guinea; P. gracilis lives only in a small area in north Queensland, and relies on sap of grass trees (Xanthorrhoea) part of the year; and Leadbeater's possum, which lives in a very small and diminishing area in Victoria. Almost all the known populations of G. leadbeateri live in a eucalypt area destined for rotary clear-felling every 50–80 years. Some other species are considered Vulnerable due to habitat loss. A captive breeding program and recovery plan has been established for Gymnobelideus. For P. australis and P. norfolcensis, recovery plans are being implemented to identify habitat threats, protect key habitats, etc.
Significance to humans
Petaurus breviceps are currently becoming more and more popular as pet species, with a varying degree of adequacy in husbandry techniques. There is some welfare concern about this, and imports from New Guinea might be illegal and of future conservation concern.
Species accounts
Sugar gliderYellow-bellied glider
Leadbeater's possum
Striped possum
Resources
Books:Flannery, Tim F. Possums of the World. Chatswood, Australia: Geo Production, 1994.
Goldingay, Ross L., and Rodney P. Kavanagh. "The Yellow-bellied Glider: A Review of Its Ecology and Management Considerations." In Conservation of Australian Forest Fauna, edited by D. Lunney. Mossman, Australia: Royal Zoological Society of NSW, 1991.
Goldingay, Ross L., and John H. Scheibe, eds. Biology of Gliding Mammals. Fürth, Germany: Filander Verlag, 2000.
Kennedy, Michael, ed. Australasian Marsupials and Monotremes. An Action Plan for their Conservation. Gland, Switzerland: IUCN Publication Department, 1992.
Salamon, Birgitt. The Consequences of Social Dominance in the Sugar Glider (Petaurus breviceps). University of Erlangen, Nürnberg PhD dissertation, 1998.
Strahan, Ronald, ed. The Australian Museum Complete Book of Australian Mammals. Sydney: Australian Museum, 1995.
[Article by: Udo Gansloßer, PhD]
