A.C. Robinson

The Southern Pigmy Possum is one of the smallest possums in Australia. These charming creatures are widely distributed in the mallee and mallee heath areas of southern Australia from the "Sunset Country" in north-west Victoria to the south west of Western Australia. At a time when many of our native marsupials appear to be either extinct, or substantially reduced in range, the Southern Pigmy Possum appears to be successfully holding its own wherever reasonably large areas of mallee scrub occur. 

Only a very few years ago, however, a statement that Pigmy Possums were common would have caused raised eyebrows among mammologists. 

There rare animals very infrequently come to the notice of science, usually when an interested farmer found a "funny mouse" in an old bag in a shed or when that finest of Australian mammal collectors, the household cat, deposited the body of a pigmy possum on the lounge room floor. 
One of the first records of this species from Innes National Park, for example, was donated to the Ranger by his pet cat. Since these times, however, people interested in finding out about the distribution of our native mammals have begun to use a new trapping technique known technically as ‘pitfall trapping’ using a drift fence. 
 

It has been known for years that postholes dug for fencing and left unfilled overnight occasionally caught small animals which fell in and were unable to climb out. Pitfalls have been used for many years to catch lizards and have been modified to make them more efficient traps. Today, a line of deep tins are buried with their lips flush with the ground surface and then a small fence about 20 centimetres high is run across the middle of the pitfall openings and between adjacent tins. This has the effect that a small animal moving along the ground, reaches the fence and turns along it until it gets to a pitfall and falls in, to await release the following morning, by an inquisitive scientist. 
 

Since mammal collectors have adopted this technique, the number of pigmy possums caught has increased enormously to a point where they are now considered relatively common mammals in suitable habitat. 
 

Just what is "suitable habitat" for pigmy possums? 

To the uninitiated the remaining tracts of mallee vegetation appear as a featureless mass of multi-stemmed trees, all too easy to get lost in if you wander away from the road. Closer examination, however, reveals that the plants under the trees (and in fact, the trees themselves) vary enormously. It appears that in any area of mallee, pigmy possums are likely to be found in the area with the greatest number of plant species. In short, the most diverse type of vegetation. 
 

This is easily understood when it is considered that pigmy possums eat insects and the nectar and pollen from flowers. Areas with a lot of different species of plants are more likely to have flowers available throughout the greater part of the year and the insects supported by such an area provide a protein rich bonus for the resident pigmy possums. 
Consideration of the diet of pigmy possums brings us to another fascinating and still little known aspect of their biology. This is their ability to go into torpor of hibernation. 
At certain times of the year, presumably in response to food shortages, low temperatures, or a combination of both, pigmy possums seek out a secure shelter and lower their body temperatures, roll up into a ball and enter torpor. It is in this state that people find these tiny creatures in old yakka stumps or in farm machinery left out in paddocks. 

Metabolic rate 

The animals are quite cold to the touch and on first sight appear to be dead. However, a minute or so of warmth from the pocket or hand awakens them from their torpid state to a point where they can move like quicksilver, and many a potential curiosity has disappeared back into the bark under these circumstances. 
 

Periods of torpor probably enable pigmy possums to lower their metabolic rates sufficiently to survive in periods of food shortage or cold weather when their insect food is either inactive or in a similarly dormant state such as caterpillars in cocoons deep in the ground. 
However, this is not the pigmy possum’s only defence against hard times. They are able to store quantities of fat in their body tissues and tails and utilise these fat stores slowly during torpor. This stored fat also provides a source of energy readily available for arousal from the torpid state. 
 

This process which only takes a few minutes may seem to us to require an insignificant amount of energy but for a tiny animal like the pigmy possum, the tightrope between energy input from food or fat stores and energy output through activity is fine indeed and can literally mean the difference between life and death. An animal forced into torpor without sufficient fat stores to allow adequate arousal will actually starve to death. 
 

The Southern Pigmy Possum, being a typical marsupial, produces young in a relatively undeveloped state compared with eutherian mammals such as ourselves. These young, however, have well developed claws on their front limbs and a good sense of smell. 
 

After birth they climb, unaided by their mother, into the pouch where they attach to one of the nipples. The end of the nipple swells inside the pouch young’s mouth so they are firmly attached and then follows a long period of development, firstly within the pouch and then in a nest built by the mother. 
 

The process of marsupial birth still holds a fascination but think of the implications in the pigmy possum, an animal where the adult only measures 16 centimetres from nose to tail tip. The female Southern Pigmy Possum produces six young at a time, each only a little over 1 millimetre at birth, and these tiny living creatures make the momentous journey from the birth canal to the pouch unaided. 
 

Most Australians will come no nearer to these tiny marsupials than the image of their close relation, the Feathertail Glider on the one cent coin. However, pigmy possums are one of the characteristic native mammals of the mallee and, for those lucky enough to see them, they almost provide sufficient reason in themselves for preserving a reasonable sample of our mallee areas.