Fauna rescue during a vegetation clearing program

The Common Brushtail Possum (Trichosurus vulpecula hypoleucus) is frequently encountered in the treed areas of the south-west of Western Australia. It will cohabitat with humans in towns and cities, often being a nuisance by occupying the roof space of houses near bushland and making deep guttural cough and sharp hissing sounds at night when people are trying to sleep.

In Western Australia its distribution extends east to Esperance and as far in land as Laverton, but is presence in arid areas is now very rare. It is a mobile, nocturnally active species that spends the day in a tree hollow, fallen log, rock cavities, and in urban areas, spaces between the ceilings and roof. It will readily travel on the ground (and thus can be killed as it crosses roads), but is agile enough to rapidly move along fence tops and its sharp claws enable it to easily move around in trees, often on slender branches.

Males are slightly larger than females growing to a mass of 4.4kg and females to 3.5kg (Kerle and How 2008). Brushtail Possums found in the south-west of Western Australia have a silvery-grey dorsal surface with a light-grey to white belly. Some of the Western Australian individuals have a white tipped tail.

During fauna salvage programs in areas where the vegetation is being cleared, there are three strategies for removing possums:

• trapping;
• lowering trees; or
• removing them from hollows.

Trapping is effective as they will readily enter a baited trap, however, it can be difficult to catch all the Brushtail Possums in an area prior to vegetation clearing without an extended trapping program. Gently lowering trees to the ground during the clearing program often enables possums to exit the tree and move to another area, however, the primary problem with this approach is that possums will move to adjacent trees and the process has to be repeated increasing the possibility that it will get injured. In some cases, the possums will remain in the tree hollow when the tree is on the ground requiring it to be extracted from a hollow, which can be a difficult task and often results in the person being bitten. The third alternative is to retrieve possums from the tree hollows before the trees are lowered to the ground.

Removing possums from hollows in large tuart or jarrah trees can problematic. An elevated work platform in the form of a cherry picker is required, and a chain saw in necessary to access parts of the tree containing hollows, and to open or expose tree hollows so that possums can be caught. In areas of natural bush on the Swan Coastal Plain, it can be very difficult driving and manoeuvring a cherry picker across sand and into the right position. Getting bogged is an obvious hazard and must be planned for. Large cherry pickers can weigh many tons and readily sink into soft coastal sands, they are not easy to manoeuvre around trees, shrubs, rocks and other obstructions, and once bogged can be difficult to extract. Brushtail Possums will readily move across the ground to access neighbouring trees, houses and sheds and will den in numerous locations over successive nights. So inspecting and removing possums from a tree during the day does not guarantee that another possum will not occupy the same tree hollows on a subsequent day. Once inspected and possums removed, trees need to be felled or all of the suitable denning hollows removed.

Recently, Terrestrial Ecosystems trapped an area of about 13ha on the Swan Coastal Plain over a period of five nights to catch a number of Brushtail Possums. The remaining possums were all caught and relocated immediately prior to vegetation clearing. Many of the large tuarts contained multiple hollows, and scratches on tree trunks indicated that some trees had been climbed frequently by possums. Some of the tuarts were nearly 40m high and had multiple large dead hollow branches near the top. In some circumstances it was not possible to see all hollow entrances from the ground.

The first task was to have the bee hives removed. A couple of the very large trees contained a bee hive in one section and Brushtail Possums using another section as a diurnal retreat. However, as a general rule, trees containing bee hives don’t normally support possums, but in the very large trees, possums can move around in the tree canopy avoiding the bees.

Tree hollows were searched for possums using two approaches: climbing the tree and inspecting hollows and removing possums where appropriate; and accessing tree hollows using a cherry picker. We used the guys at West Coast Arbor Service to climb trees and to use the various elevated platforms to trim branches, expose hollows and retrieve Brushtail Possums. Working in tall trees is not for the faint hearted and removing branches to access hollows requires skill with a chainsaw. Empathy for possums is also important, as it must be a frightening experience for a possum to be denned up in a tree hollow when people are using a chain saw to get access to that part of the tree. In some circumstances it was possible to expose the hollow so that the possum can be caught by hand and placed in a bag. On other occasions, a section of a branch or tree trunk had to be carefully removed with the possum still in the hollow and lowered gently to the ground. Manoeuvrability and ability to access a tree hollow is often easier of the ground than it is in the bucket of a cherry picker.

In this project, all trees in the project area that contained hollows that could provide suitable diurnal retreats for possums and other small fauna were inspected, and where possums were present, they were safely removed and relocated to another location.

Well done to all involved. It was a successful project undertaken safely, with lots of rescued fauna.

Reference

Kerle, J. A. and R. A. How. 2008. Common Brushtail Possum. Pages 274-276 in S. Van Dyck and R. Strahan, editors. The Mammals of Australia. Reed New Holland.