It has been known for some time that the Western Pygmy Possum Cercartetus concinnus is resident at the Observatory (Eyre Report 2 1979-1981). Trapping results suggested that it may be relatively abundant, but little quantitative information has been gathered. A nest box had been placed in the large mallee Eucalyptus diversifolia next to the solar energy unit but had not been used. When a Pygmy Possum took up residence in June 1987 and built a nest it was decided to build more boxes immediately, and add to their number as opportunity allowed.
We wanted to know:
a) whether the Pygmy Possums would follow the example of the female in box 1 and use the boxes for breeding and/or sanctuary
b) if they would move from one type of mallee to another following the flowering and
c) if the abundance of Pygmy Possums varied in the site area
Nine nest boxes were completed and erected in July 1987, 10 more in August, 12 in September, and 19 in October. These boxes were made in a variety of ways, openings were not standard but only the boxes with small openings were used by the Pygmy Possums.
The trees selected were all mallee species: Eucalyptus diversifolia (16 boxes), E. angulosa (17 boxes), and E. rugosa (18 boxes). Peak flowering for these species was July to September, October to December and November to December respectively. Most boxes were placed about 1.5m - 1.8m from the ground. Boxes were inspected weekly from June to December 1987, fairly regularly in January 1988, not in February and once in March. The regular inspections did not appear to disturb even the females with young, particularly once a nest had been established.
Initially individuals were marked with felt pen at the base of the tail using up to four colours and lasting for up to two months. Later an ear clipper was used to provide permanent identification.
Pygmy Possums used 38 of the 51 boxes. Boxes not used on a regular basis were sometimes taken over by other creatures, such as huntsman spiders. On two occasions occupancy by individual huntsman spiders exceeded 3 months.
A very large cricket occupied box 28 for two months and Marbled Geckoes Phyllodactylus marmoratus were found briefly in two boxes.
Female Pygmy Possums occupied boxes for longer periods than males if they constructed nests, but generally non-breeding females were transitory. This was also true of females with tiny young who did not begin a nest. Males were much less prone to stay in a nest. The “top resident” female occupied the same box for 19 consecutive visits (18 June -
7 November 1987).
Resident females were the nest builders with long-term female residents always building substantial nests. Nests filled the boxes over time, with leaves renewed on an ongoing basis. Early nests were constructed of the host mallee, but later the leaves of Acacia anceps were more commonly used. These large shrubs were 20 - 30m from the nest tree.
During the period of the study 29 females had a total of 34 litters. Numbers in each litter varied, ranging from 6 to 2. It seems possible that the nest boxes provided secure areas as observations showed all of the young counted produced by one female survived up until the time they became independent. Litters were found during the following months: June (1), July (1), August (4), September (10), October (6), November (9) and December (3). The 15 litters that contain known numbers provided 28 males and 35 females, for a total of 63 at an average of 4.2 young per litter.
Out of a total of 169 individuals marked, 34 were later found in different boxes or places. The distances covered ranged from about 3m to a little over a kilometre. Regularly caught males and females tended to be found in a relatively confined area, on average from 10 to 250m, 100m being the norm. Nine individuals made longer treks: two movements of about 500m, three of about 700m and four of about 1000 m.
Pygmy Possums were found to readily enter and use human habitation. We caught them in the house and two bred in the garage. No success was had when searching for nests in hollows or in old Babblers’ nests.
We had one female (non-gravid) that went from 14.6g on 13 December 1987 to 27.5g on 9 January 1988. She was in boxes with other possums for four observations and the fifth time alone. Possibly cannibalism is an explanation for the acceleration in weight.
We found no evidence to support Smith’s contention that Pygmy Possums were often found in a torpid condition and could be handled without them being aware of it.
This survey demonstrated that Pygmy Possums will regularly and frequently use breeding boxes.
Despite the shortness of the survey, it seems likely that they move from one blossoming species to another. What happens when the mallees stop flowering is unknown, although we think they may use the mistletoe that flowers during February to March. We were unable to discover whether they move into the Melaleuca that blossoms during the same period and later.
It may well prove significant that in 1988, which saw almost no flowers on the mallees, there were very few Pygmy Possums sighted.
Probably, the most important outcome of this study has been its demonstration of the need for a more extensive and intensive study program over a number of years, ideally undertaken by an independent researcher. The material gathered during 1987, despite its many shortcomings, would be a valuable starting point.
Royal Australasian Ornithologists Union, (1982). Eyre Bird Observatory Report 1979-1981, West Australian Group, Perth.
Smith M.J. (1983). The Western Pygmy Possum. In R Strahan (Ed)
The Australian Museum Complete Book of Australian Mammals (Sydney, Angus and Robertson)
In 2004, Rod Smith made some new Western Pygmy Possum nest boxes as the old wooden ones were on their last legs. Pygmy Possums are still enjoying the environs of the Observatory and have accepted their new PVC pipe style accommodation very well.
They have occasionally taken over the box for putting the Rope Walk booklet in. A check is made every morning so guests know to be careful not to squash the sleeping possum when they return the booklet.
We have had possums sleeping in the top bunk of the V.I.P. room much to the amusement of guests. A Pygmy Possum has even surprised us in the Stevenson’s Screen (weather instument box).