Leadbeater's Possum
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[Photo] Leadbeater's Possum featured on an Australian 5 cent stamp as an endangered species

Leadbeater's Possum (Gymnobelideus leadbeateri) is an endangered possum restricted to small pockets of remaining old growth mountain ash forests in the central highlands of Victoria, Australia north-east of Melbourne. Leadbeater's Possums can be moderately common within the very small areas they inhabit: their requirement for year-round food supplies and tree-holes to take refuge in during the day restricts them to mixed-age wet sclerophyll forest with a dense mid-story of Acacia. It is the only species in the Gymnobelideus genus. It was named after John Leadbeater the then taxidermist at the Museum of Victoria.

History
The possum was not discovered until 1867, originally known only through five specimens; the last one collected in 1909. From that time on, the fear that it might be extinct gradually grew into near-certainty after the swamps and wetlands around Bass River in south-west Gippsland were drained for farming in the early 1900s.

In 1961, a colony was discovered near Marysville, in the Upper Yarra Valley. Extensive searches since then have found the existing population in the highlands. However, the availability of suitable habitat is critical: forest must be neither too old nor too young.

A formerly fairly healthy population was ascribed to the terrible Black Friday fires that swept through Australia in 1939: The combination of 40-year-old regrowth (for food) and large dead trees left still standing after the fires (for shelter and nesting) allowed the Leadbeater's Possum population to expand to an estimated peak of about 7500 in the early 1980s (since declining to 2000). However, the old trees are gradually decaying and the regrowth is maturing. Prior to European settlement, a similar situation would have forced migration to other areas???something which is not a realistic option now because of extensive land clearing over the last hundred years or so.

From its peak in the 1980s, the Leadbeater's Possum population is expected to further decline rapidly, by as much as 90%. The population has dropped sharply since 1996, when it was listed as Critically Endangered. Failing human intervention, and assuming that a population of about 1000 can survive that long, natural tree hollows will begin to develop in the Black Friday regrowth as the trees reach about 150 years of age in the second half of the 21st century, and numbers begin to climb again.

Habits
Leadbeater's Possums are rarely seen: they are nocturnal, small (about 16 cm long and about 130 grams, or the size of a small rat), fast-moving, and occupy the upper story of some of the tallest forests in the world. They live in small family colonies of up to 8 individuals, usually a breeding pair, their offspring, and sometimes an unrelated extra male or two. All members sleep together in a nest made out of shredded bark in a tree hollow, anywhere from 6 to 30 metres above ground level and roughly in the centre of a territory of 10,000 to 20,000 square metres, which they defend actively. The senior female is the main defender: she is more active in expelling outsiders, and attacks her daughters when they reach sexual maturity at about 10 months of age, forcing them to disperse earlier than male children. In consequence, mortality among young female Leadbeater's Possums is high???average female lifespan is little more than 18 months, as opposed to about 7 years in captivity.

Solitary Leadbeater's Possums have difficulty surviving: when young males disperse at about 15 months of age, they tend to either join another colony as a supernumerary member, or gather together into bachelor groups while they await an opportunity to find a mate.

At dusk, Leadbeater's Possums emerge from the nest and spread out to forage in the canopy, often making spectacular leaps from tree to tree (they require continuous understory to travel). Their diet is omnivorous: they take a range of saps and exudates, lerps, and a high proportion of arthropods which they find under the loose bark of eucalypts: spiders, crickets, beetles, and the like. Plant exudates make up 80% of their energy intake, but the protein provided by the arthropods is essential for successful breeding.

Births are usually timed for the beginning of winter (May and June) or late spring (October and November). Most litters are of one or two young, which stay in the pouch for 80 or 90 days, and first emerge from the nest about three weeks after that. Young, newly indedpendent Leadbeater's Possums are very vulnerable to owls.

Status
In 1971, the State of Victoria made Leadbeater's Possum its faunal emblem.

Endangered and with a range limited only to the Upper Yarra Valley, logging continues to pose a critical threat to Leadbeater's possum. The logging in 1993 of "much of the possum's habitat, know as zone one" a five hectare reserve east of Powelltown, followed a "mapping error." Author, Peter Preuss, stated that the possum's population faltered in 1997 with current habitat (limited to a 50-square-kilometre area) under threat from logging. He emphasised the need to relaunch a breeding program.

Dr. David Lindenmeyer (Australian National University) has argued that the need for nest boxes indicates that logging practices are not ecologically sustainable, for conserving hollow-dependent species like Leadbeater's possum. Studies have shown that clear-felling operations, such as the logging run in state forest between the Yarra Valley National Park and Mount Bullfight Conservation Reserve in February 2006, lead to the deaths of most possums in the area - "Adult animals have a strong affinity with their home range and are reluctant to move".

Despite a joint Federal and State government plan to save it, since the 1980s, the Leadbeater's possum population has halved to around 2000. Many more were killed early in 2007 when VicForests bulldozed large firebreaks through Leadbeater's monitoring stations following the Christmas fires - firebreaks and clear-felling also prevent breeding with nearby colonies.

Following the death of the last Leadbeater's Possum at Healesville Sanctuary Victoria in May 2006, there are now no Leadbeater's Possums in captivity anywhere in the world and so no breeding program to assist this animal's survival. The formation of the group, Friends of Leadbeater's Possum is a positive step towards raising the profile of this unique animal and an opportunity to continue to lobby the State Government to properly protect its declining habitat.

http://en.wikipedia.org/wiki/Leadbeater's_Possum

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