The mountain pygmy possum (Burramys parvus), also called the burramys, is a small, mouse-sized marsupial found in Australia. It weighs about 45 grams (1.6 ounces) and lives in dense alpine rock screes and boulder fields, mainly in southern Victoria and near Mount Kosciuszko in Kosciuszko National Park, New South Wales. These areas are at heights between 1,300 to 2,230 meters (4,270 to 7,320 feet). The possum’s tail, which is 14 cm (5.5 inches) long, is longer than its head and body combined, which measure 11 cm (4.3 inches). Its tail is hairless, while its body is covered in thick, soft grey fur, except for its belly, which is cream-colored. The female has a pouch on its underside with four teats. This animal eats insects, such as the bogong moth, fleshy fruits, nuts, nectar, and seeds. It is the only living species in the genus Burramys and the only Australian mammal that lives exclusively in alpine habitats.
Discovery
The mountain pygmy possum was first found in fossils from 1895. These fossils included part of the jaw and skull bones discovered in the Wombeyan Caves in central New South Wales. At that time, scientists thought the species had gone extinct. A live individual was later found in 1966 at a ski resort on Mount Hotham in Victoria. Since then, the mountain pygmy possum has been identified in three separate groups living in mountain areas of southern Australia. These groups are genetically different from each other.
Description
The mountain pygmy possum is a small animal related to rodents. It weighs about 45 grams (1.6 ounces) and has a body length of approximately 110 millimeters (4.3 inches). Males are slightly larger than females. These animals have large, forward-facing eyes and short, pointed snouts. Their teeth include three upper front teeth and two upper premolars. Their hind feet have a special feature called an opposable hallux. They also have a pouch that opens toward the front and contains four teats. Their bodies are covered in fine, thick fur. The fur is greyish-brown on the back, with a darker stripe down the middle of the back, and pale cream on the belly. They often have a dark grey ring around their eyes. During breeding season, males develop a tawny-orange color on their stomach and sides. The mountain pygmy possum has a long, prehensile tail that averages about 140 millimeters (5.5 inches) in length and has sparse hair.
Habitat and geographic range
The mountain pygmy possum is found only in the alpine areas of southern Australia. This species lives in three separate 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 areas where these animals live differ between males and females. Female mountain pygmy possums usually live at higher elevations, around 1,400–2,228 meters (4,593–7,310 feet), near block streams and deep boulder formations. The size of a female’s home range depends on the number of bogong moths, which are their main food source. At higher elevations, where there are more moths, females have smaller home ranges. At lower elevations, where there are fewer moths, females have larger home ranges. Male mountain pygmy possums live at lower elevations, generally between 1,200–1,300 meters (3,900–4,300 feet), in these mountain areas. Male home ranges are largest during the breeding season, which happens between November and December, when they move to where females are nesting. After the breeding season, their home ranges become smaller.
Foraging habits and behaviour
Mountain pygmy possums prefer to eat bogong moths, which make up about one-third of their diet. These moths (Agrotis infusa) move to high alpine mountain areas during spring and summer. During these seasons, the possums mainly rely on bogong moths for food. In autumn, the moths leave the mountains, and the possums must add other foods to their diet, such as fruits and seeds. Burramys parvis species also eat the mountain plum pine, which comes from the conifer Podocarpus lawrencei, as well as seeds from snow beard-heaths (Leucopogon spp.) and blackberries (Rubus spp.). When finding food, the mountain pygmy possum first smells the item, then uses its incisors to pick it up. The possum moves the food to its forelimbs to handle it and tear off pieces of flesh.
Reproduction
Mountain pygmy possums have a yearly reproductive cycle. Even though female possums can have multiple breeding cycles, the need for enough fat during hibernation limits them to one litter each year. To build enough fat, female mountain pygmy possums reproduce in spring, when bogong moths are plentiful. The breeding season usually happens in October and November, which are the spring months in Australia. During this time, males travel to the higher elevation nesting areas of females to mate. After mating, the female has a pregnancy lasting 14–16 days. The young, which are born helpless, enter the forward-facing pouch of the female. A female has four teats, and a litter usually includes three to four offspring. The young stay in the pouch for about three weeks, then remain at the nest for another three to four weeks. They are weaned at around nine to ten weeks. The mating system of Burramys parvus is called resource defense polygyny. A group of female possums that stay in the same area share nesting spaces in deep boulder crevices. These nesting areas are places where many bogong moths pass through. Soon after the breeding season, females push the male possums away from the nest. Male mountain pygmy possums do not help care for the young. Young male possums are also driven from the nest shortly after weaning. As seen in all Burramyid species, mountain pygmy possums reach sexual maturity by the age of one year.
Behaviour
Mountain pygmy possums are active at night and sleep during the day. Unlike other animals in the Burramyidae family, which live in trees, mountain pygmy possums live on the ground. These small mammals prefer to live in areas with large rocks in the high mountain regions of southern Australia. Female mountain pygmy possums often stay in groups of up to 10 related individuals. They tend to stay in the same area and return to the same nesting spots regularly.
Male mountain pygmy possums usually live alone. After reaching maturity, males leave their nesting areas and move to lower parts of the mountains. Because of this, males often face greater risks of dying than females, as the rocky areas where females live provide some protection from predators. Burramys parvus is the only small mammal in Australia that hibernates for long periods each year. Other members of the Burramyidae family may hibernate only when needed.
Adult mountain pygmy possums hibernate for up to seven months, while young possums hibernate for about five months. Both males and females depend heavily on bogong moths for energy and to gain weight before hibernation. These possums also store seeds and berries, which they eat when they wake up during hibernation. During hibernation, Burramys parvus wakes up every two to three days to eat stored food. These awakenings usually happen when the outside temperature is between 4–7 °C (39–45 °F). During hibernation, the mountain pygmy possum can lower its body temperature to 2 °C (36 °F). To stay warm, the animals curl their bodies and tuck their heads into their chests or stomachs. Female possums sometimes share nests made of moss and grass. Both males and females hibernate under a layer of snow for insulation.
During the spring and summer breeding season, older and heavier mountain pygmy possums usually live in the best habitats. While males are generally peaceful with each other most of the year, they may fight during the breeding season. Both males and females show aggression by biting each other’s tails. Females are especially aggressive when protecting their nesting areas, especially if their young are nearby. After the breeding season, females also act aggressively toward adult males and juvenile males after they stop nursing.
Conservation status
Since 2008, the mountain pygmy possum has been listed as critically endangered by the IUCN Red List. In 2000, population estimates showed fewer than 2000 individuals across three separate populations. Recent studies show these numbers have dropped sharply over the last decade. A 2006 study at Mount Buller found only 30 adult possums. In 2007, 60 individuals were recorded at Mount Blue Cow and Kosciuszko National Park. By 2021, scientists still estimated fewer than 2000 individuals remained.
The biggest threats to the mountain pygmy possum include habitat loss, climate change, predation by feral cats and red foxes, and the decline of the bogong moth, which is their main food source.
The construction of ski resorts in alpine areas has greatly reduced possum numbers. At Mount Higginbotham, a road built for the Mount Hotham ski resort blocked male possums from reaching female nesting sites during breeding season. This barrier increased winter deaths among the population. To help, a tunnel was built to allow males to move safely.
Climate change is a major threat. Burramys parvus is the only Australian mammal that lives only in alpine regions. It depends on the seasonal availability of bogong moths and other food. Studies in Kosciuszko National Park found that snow cover lasted 10 days less and melted 15 days earlier than before. Researchers, including Linda Broome, found that snow provides extra insulation during cold months, helping possums stay in a deep sleep (hibernation) longer. Broome suggested moving possums to lower-elevation rainforests, as previous studies showed they do not need to hibernate when temperatures are above 12°C (54°F).
Predation by red foxes and feral cats also harms the species. Threat abatement plans are in place to reduce these dangers and protect affected species.
The survival of the bogong moth, the possum’s main food, is also critical. These moths arrive in spring, signaling the end of hibernation for possums. They provide the energy needed for the seven-month hibernation period.
Captive breeding programs have been started to help the species. Linda Broome and her team, along with Zoos Victoria, began a program in 2007 at Healesville Sanctuary. By 2013, 45 possums were cared for in the program. The goal is to reduce the species’ threat level on the IUCN Red List.
A new captive breeding project, Secret Creek Sanctuary in Lithgow, New South Wales, started in 2021. Prague Zoo donated A$190,000 after the 2019–20 bushfires, and the Australian Wildlife Society also provided funding. About 15 possums will be captured from Mount Kosciusko, acclimated in enclosures, and released into the sanctuary.
In 2016, the first national recovery plan was created under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999. The plan aimed to address habitat loss, predators, and climate change, especially for the small population at Mount Buller. It outlined the species’ distribution, habitat, threats, and steps to ensure its survival.
In 2018–2019, a large drop in bogong moth numbers was observed due to droughts caused by climate change. Without enough moths, possums lost litters in 2018 because of poor nutrition. A similar situation in 2017 led to predictions of declining adult numbers.
During the 2017–2018 and 2018–2019 seasons, millions of bogong moths typically filled Alpine caves, but some caves had none. Eric Warrant of Lund University linked the drop to droughts in the moths’ breeding areas and climate change, which reduced vegetation for moth caterpillars.
Other scientists noted that the decline in moths affects many animals that rely on them for food, including the mountain pygmy possum and other insect-eating mammals and birds. Euan Ritchie, a wildlife ecologist from Deakin University, stated that the Australian Alps are among the most vulnerable to climate change because the mountains are small, leaving cold-adapted species with no place to move as temperatures rise.