Pygmy Possum Nest

Pygmy Possum Nest-Box Project

Don Hird

Tasmania has two species of pygmy possums, both of which are also found on mainland Australia and on some offshore islands. The Little Pygmy Possum Cercartetus lepidus is around 7g, while the Eastern Pygmy Possum Cercartetus nanus is around 24g (Complete Book of Australian Mammals). These possums are mice-sized, very secretive, and not very much is known of their natural history.

The biology of Pygmy Possums is not particularly well known, especially in Tasmania. This is largely due to the difficulty of trapping live animals for research purposes. Nonetheless, they are sometimes encountered by firewood cutters (probably animals disturbed from tree hollows) and through domestic cats bringing them home as prey. From these sources they are often brought into Animal Rescue shelters in Tasmania. Other observations come from chance encounters by such people as bushwalkers and birdwatchers, and from wildlife surveys. Generally, though, very few people see Pygmy Possums and they are notoriously difficult to find.

< Eastern Pygmy Possum
(photo: Geoff Fenton/ Qug McKendrick)

In the late 1990s researchers in New South Wales (NSW) trialled the use of nest-boxes as a possibly superior detection method to conventional live-traps for small mammals. It was discovered that specially designed boxes could be used effectively, and that in some places sufficient captures were made to allow population studies, the first of their kind in that State. Researchers involved with this study found that about 50% of boxes were occupied by Pygmy Possums and some other small native animals, effectively the boxes become surrogate tree hollows which are often a scarce/limiting resource. Pygmy Possum presence was also detected by the presence of fresh green leaves as nesting material in nest-boxes. Information collected included details of the growth, social groupings, diet (through pollen sampling) and movement between nest-boxes. Nest-boxes which were successful had a particular design which allowed small animals to enter the boxes while larger animals were excluded.

This project has now deployed over 200 nest-boxes modelled on those used in NSW. These are located in a range of areas in southern Tasmania. In collaboration with Forestry Tasmania, part of this project (96 nestboxes) is incorporated into the Warra Long Term Ecological Study area in the southern forests. By placing nest-boxes in areas of forest subjected to alternative harvesting regimes, the relative value of forest practices for pygmy-possums will be compared, and advice offered to the forestry industry accordingly. Other information will be collected on characteristics of sites at which each species of Pygmy Possum occurs (i.e. habitat preferences), distribution and abundance, and whether both species occur together at some sites.

Other nestbox deployment areas include Bruny Island (montane cool-temperate rainforest and coastal shrubby woodland), Mt Morrison (dry open eucalypt forest) and Eaglehawk Neck (coastal forest with shrubby understorey).

Data collected will be assessed in collaboration with a doctoral student (Jamie Harris) under the supervision of Dr Ross Goldingay (Southern Cross University) and staff of the Zoology Department of the University of Tasmania (Associate Professor Randy Rose) for publication of results in scientific journals.

< Eastern Pygmy Possum
The fattened base of the tail helps distinguish pygmy-possums from rodents.
(photo: Geoff Fenton/ Qug McKendrick)

The specifications for the nest-boxes used in NSW are as follows. External dimensions of the nest-boxes were 17 cm by 17 cm and 25 cm tall, constructed from rough sawn pine 18 mm thick. Each box had a hinged lid and a 15 mm gap across the front under the lid to allow animals to enter. Boxes are suspended from trees from the back of the boxes. The bottom of each box was perforated to allow for any necessary drainage. For simplicity a nest-box with a clip-in lid rather than a hinged lid (the most fragile part of the original design) has been used.

Design and Technology students at Clarence High School built many of the nest-boxes using mass-production methods in order to allow the project to proceed on a cost-effective basis. Sponsors have donated materials for the project and more will be sought from suitable donors.

Because of the significant logistics involved in deploying 200+ nest-boxes, members of the public with an interest in natural history and ownership or access to suitable sites are assisting in monitoring some boxes. This activity is supervised by a qualified ecologist with appropriate permits and experience in studies of native mammals. The study will investigate pygmy possums in their natural habitats; animals will not be removed or relocated although individuals may be marked for re-identification using established, humane methods. Nest-boxes will be deployed so as not to be easily evident to the general public.

Pygmy Possum Nest-box Project

Progress Report, October 2007

This Progress Report describes the current implementations of nest-boxes, and some plans for further deployments.
Four main study areas have been established, representing a range of habitat types in south-eastern Tasmania, as follows.

Wet forest is represented at two sites.
The Warra Long Term Ecological Research area is in the southern forests a short distance across the Huon River from the Tahune Airwalk tourism facility. This area has been extensively studied and is known as habitat for the two species of pygmy possums found in Tasmania. Dominant trees are very large Eucalyptus obliqua with an understorey comprised of rainforest trees and shrubs and copious cutting grass. This particular study area has a nest-box deployment pattern designed to test the efficacy of “retained aggregates” of trees in clearfell coupes, with replicated numbers of nest-boxes in both retained aggregates and pseudoaggregates in nearby control coupes of intact forest. Ninety six nest-boxes are in place at Warra.
The second wet forest area is in the vicinity of Mount Mangana, Bruny Island, a habitat dominated by Nothofagus cunninghamii and other rainforest species with occasional Eucalypts. This area is checked by Tonia Cochrane of Inala Nature Tours and has been established partly based on a chance sighting of a little pygmy possum foraging in daylight on a Richea dracophyllum blossom. Ten nest-boxes are in place with a similar number of further deployments planned. Also planned for wet-forest are ten nest-boxes in wet forest with abundant Leatherwood (Eucryphia lucida), and thus a seasonally rich supply of nectar and pollen, in the Tahune Airwalk vicinity.

Coastal and intermediate habitats are represented in two main areas at present. Further to the wet-forest areas on Bruny are 15 nest-boxes currently deployed in dryer coastal forests and tall heathlands. Blue-gum habitat with its seasonally rich supply of nectar and pollen is of interest and may be investigated further. On Tasman Peninsula twenty five nest-boxes are deployed.

Dryer forest habitats are being investigated in the Mount Morrison forestry district NE of Hobart where twenty eight nest-boxes are now in place.

Deployment commenced in January 2007 and thus far approximately 180 nest-boxes are in place, as described above. Checking commenced in April 2007 but no vertebrates have yet been found in nest-boxes. Some practical issues involving better waterproofing of nest-boxes and more suitable methods of fixing the lids are being addressed. Other developments arising from this project involve various records of pygmy possums being reported, some of which may lead to further investigation using nest-boxes, or possibly other devices such as automated cameras.

Don Hird gratefully acknowledges provision of timber for nest-boxes from Auspine P/L and a financial contribution from Norske Skog Ltd. Further offers of assistance towards expenses for this project are welcome and will be suitably acknowledged.

Pygmy Possum Nest-box Project

Progress Report, November 2009

Further to the prior Progress Report, more recent developments are described here.

Deployment of nest-boxes on Bruny in dryer coastal forests and tall heathlands has been extended to a total of 50 boxes. Other deployments are as previously noted although some of the Eaglehawk Neck boxes were reportedly damaged by fire.

Monitoring has been of the order of a maximum of three months between visits as other commitments and limitations on the researcher have allowed.

The first pygmy possum seen as part of this project was in a retained forest aggregate at Warra. The animal had evidently made a spherical nest of woven Eucalyptus obliqua bark in the box in which it was found. It escaped without being marked. Another nearby box in the same aggregate has since been observed to contain a similar nest.

On Bruny Island only coastal woodland has revealed evidence of pygmy possums. The first sign of occupancy was observed less than three months after initial deployment of boxes, in early 2008. At first animals were observed in bare boxes, but subsequently spherical nests of woven plant materials and many animals have been observed. Again, handling and marking of animals has proved difficult so that only photographic and observational information has been obtained. It appears that both Tasmanian pygmy possum species are present at this site and that distinctive nests are constructed by each. Nests tentatively ascribed to little pygmy possums are substantially made from green moss while those suspected to be made by eastern pygmy possums utilize shredded bark as their principle material. Overall utilization of boxes at this site is indicated by about 40% having at least some incorporated nesting material and up to 20% containing one or more animal on any one inspection.

No adverse effects on any animals have been observed in the course of this project so far.

Don Hird

For more information, or to participate, contact Don Hird at donald.hird@education.tas.gov.au

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