The mountain pygmy possum (Burramys parvus), also simply known as the burramys, is a small, mouse-sized (weighs 45 grams (1.6 oz)) nocturnal marsupial of Australia found in dense alpine rock screes and boulder fields, mainly southern Victoria and around Mount Kosciuszko in Kosciuszko National Park in New South Wales at elevations from 1,300 to 2,230 metres (4,270 to 7,320 ft). At almost 14 cm (5.5 in), its prehensile tail is longer than its 11 cm (4.3 in) combined head and body length. Its diet consists of insects (such as the bogong moth), fleshy fruits, nuts, nectar and seeds. Its body is covered in a thick coat of fine grey fur except for its stomach, which is cream coloured; its tail is hairless. On the underside of the female's body is a pouch containing four teats. This possum is the only extant species in the genus Burramys. It is also the only Australian mammal restricted to alpine habitat.
Discovery
The mountain pygmy possum was first discovered in the fossil record in 1895 when a portion of the jaw and skull bones were found in the Wombeyan Caves in central New South Wales. At the time, the species was believed to be extinct. It was not until 1966 that a living individual was found at a ski resort at Mount Hotham in Victoria. Since that time, the mountain pygmy possum has been located in three isolated, genetically distinct populations in the alpine regions of southern Australia.
Description The mountain pygmy possum is a small rodent-like marsupial. The mountain pygmy possum has an average weight of approximately 45 g (1.6 oz) and an average head and body length of 110 mm (4.3 in). The species is sexually dimorphic, with males being slightly larger than females. They have large, forward pointing eyes and short pointed snouts. Mountain pygmy possums exhibit diprotodont dentition, with three upper incisors and two upper premolars. On the syndactylous hind feet, they possess an opposable hallux. In addition, the mountain pygmy possum has a pouch which opens anteriorly and contains four teats. Pygmy possums are covered in a layer of fine, dense fur. Their pelage is greyish-brown on the dorsal side, with a darker stripe along the midline of the back, and a pale cream colour on the ventral side. They typically have a darker grey ring surrounding the eyes. During breeding season, males become more tawny-orange on the abdomen and flanks. The mountain pygmy possum has a long prehensile tail, averaging about 140 mm (5.5 in) in length, which is sparsely haired.
Habitat and geographic range The mountain pygmy possum is endemic to the alpine regions of southern Australia. The species is currently restricted to three isolated mountain regions: (1) Mount Blue Cow in Kosciuszko National Park in New South Wales, (2) Mount Bogong and Mount Higginbotham/Loch in the Bogong High Plains in Victoria, and (3) Mount Buller in Victoria. The typical home ranges within these mountain ranges differ for males and females. Females tend to reside at higher elevations of approximately 1,400–2,228 m (4,593–7,310 ft) near patches of block streams and other deep boulder formations. The home range of a female mountain pygmy possum is correlated with the density of bogong moths, the pygmy possum's preferred food source, which varies at different elevations. Females at higher elevations have smaller home ranges due to a relatively greater abundance of bogong moths, whereas females residing at lower elevations typically have much larger home ranges as the quantity of moths declines. Male mountain pygmy possums reside at low elevations, generally between 1,200–1,300 m (3,900–4,300 ft), of these mountain ranges. Male home ranges are largest during the breeding season, between November and December, when they migrate to female nesting sites, and decline thereafter.
Foraging habits and behaviour Mountain pygmy possums prefer to feed on bogong moths which make up about a third of their diet. This moth species (Agrotis infusa) migrates to the high alpine mountainous regions during the spring and summer months. During these months, mountain pygmy possums utilise bogong moths as their principal food source. In the autumn months, bogong moths depart from the mountain ranges and mountain pygmy possums must supplement their diets with fruits and seeds. Burramys parvis species will supplement their diet with the mountain plum pine from the fruit-bearing conifer Podocarpus lawrencei as well as seeds from the snow beard-heaths Leucopogon spp. and blackberry Rubus spp. Upon finding food, the mountain pygmy possum will first smell the food source before picking it up with its incisors. It will then transfer the item to its forelimbs so that it may manipulate the food and tear off pieces of flesh.
Reproduction Mountain pygmy possums have an annual reproductive cycle. Although females are polyestrous, the need for sufficient fat reserves during hibernation limits females to one litter per year. In order to ensure adequate fat reserves, female mountain pygmy possums will synchronise reproduction for the spring months, when bogong moths are abundant. The breeding season typically occurs during the Austral spring months of October and November. During this time, males migrate to the higher elevation nesting sites of females to mate. Mountain pygmy possums then have an internal gestation period of 14–16 days after which the altricial young will enter the forward-facing pouch of the female. A female mountain pygmy possum has four teats, and a litter is usually three to four offspring. The young remain in the pouch for approximately 3 weeks, after which they remain at the nest for another 3–4 weeks. The offspring are then weaned at around 9–10 weeks. The mating system that occurs in Burramys parvus is resource defence polygyny. A philopatric group of females typically share a nest space within deep boulder crevices. The nest sites are generally areas of high densities of migrating bogong moths. Shortly after mating season, females will drive the male pygmy possums from the nest. The male mountain pygmy possums do not participate in parental care. Additionally, juvenile males are driven from the nest shortly after weaning. As noted in all species of Burramyids, mountain pygmy possums become sexually mature by one year of age.
Behaviour
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