| Leadbeater's Possum[1] | |
|---|---|
| Taxidermy specimen | |
| Conservation status | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Infraclass: | Marsupialia |
| Order: | Diprotodontia |
| Family: | Petauridae |
| Genus: | Gymnobelideus |
| Species: | G. leadbeateri |
| Binomial name | |
| Gymnobelideus leadbeateri McCoy, 1867 |
|
| Leadbeater's Possum range | |
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.[3]
In 1968, the State of Victoria made Leadbeater's Possum its faunal emblem.
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The possum was not discovered until 1867 and was 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 in Australia around Bass River in south-west Gippsland were drained for farming in the early 1900s.[4] Then, on 3 April 1961, a member of the species was rediscovered by naturalist Eric Wilkinson, and the first specimen in more than 50 years was captured later in the month. [5]
In 1965, a colony was discovered near Marysville. 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 were gradually decaying and the regrowth 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.[4] Failing human intervention, and assuming that a reduced population could have survived that long, natural tree hollows were expected to develop in the Black Friday regrowth as the trees reached about 150 years of age in the second half of the 21st century, and numbers to begin climbing again.
However, the status of Leadbeater's Possum is in even more doubt following the disastrous bushfires that swept its only known habitat on Black Saturday in February 2009. Large areas of bushland around Marysville, Narbethong and Healesville have been destroyed.[6]
Leadbeater's Possums are rarely seen: they are nocturnal, small (about 10 cm long and about 90 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 24 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 14 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 27 months, as opposed to about 10 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 independent Leadbeater's Possums are very vulnerable to owls.
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 [sic?] as zone one" a five hectare reserve east of Powelltown, followed a "mapping error."[7] 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.[8]
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.[9] Studies have shown that clear-felling operations, such as the logging run in state forest between the Yarra Ranges 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".[10]
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.[4]
With its known habitat[11] destroyed in the disastrous bushfires of February 2009 - large areas of forest around Marysville, Narbethong and Healesville - the species status is currently in doubt.[6] The mapped distribution of the Leadbeater's possum was within the area burnt by the fires.
With few individuals having survived the fires, salvage logging since the fires has posed a further risk to this extremely diminished population , with clear-felling also approved by VicForests in the few remaining unburnt areas, such as the Kalatha Creek area of Toolangi in 2010 , a move opposed by the Yarra Ranges Shire Council. [12] [13] [14]
Following the death of Kasia, the last captive Leadbeater's Possum, at Toronto Zoo in January 2010, there are now no Leadbeater's Possums in captivity anywhere in the world and so no breeding program to assist this animal's survival.[15] The last Australian specimen held at Healesville Sanctuary died in May 2006. The formation of the Friends of Leadbeater's Possum group is seen as a positive step towards raising the profile of this animal and an opportunity to continue to lobby the State Government to properly protect its declining habitat.