Behaviour and ecology of tropical rock-possums

: the rock-haunting possum, Petropseudes dahli and the scaly-tailed possum, Wyuld squamicaudata

Abstract

This thesis describes a three-year behaviour and ecological study of two species of little known, rock-dwelling possums (the rock-haunting possum, Petropseudes dahli and the scaly-tailed possum, Wyulda squamicaudata) in the wet-dry tropics of northern Australia. Both P. dahli and W. squamicaudata occupy monotypic genera and are one of 14 species in the Pseudocheridae Family and the Phalangeridae Family respectively. Petropseudes dahli has experienced a slight range contraction and W. squamicaudata is thought to be extinct from half of its former geographical range. I focused my studies on a wild population of P. dahli in Kakadu National Park on the edge of the Arnhem Land Plateau, 300 km east of Darwin. I used nocturnal observations and radiotelemetry to study foraging behaviour, diet, movements, communication, antipredator and social behaviour of free-ranging possums. In order to compare the ecology and behaviour of P. dahli with another rock-dwelling possum, I found a population of W. squamicaudata and monitored their diet and movements and observed foraging behaviour during August 1997.

Specimen records of W. squamicaudata are sparse and patchily distributed, and the few captured possums have been associated with rocky outcrops. To investigate the ecological requirements of W. squamicaudata I used radiotelemetry to study movements and habitat usage of this species in the Mitchell Plateau, W. A. I made nocturnal observations of W. squamicaudata to determine dietary requirements and social behaviour, and combined this information with trapping to estimate population size.

Radiocollared possums (n = 5) chose a variety of rock formations for diurnal
dens. Possums foraged and denned alone and had overlapping home ranges (crude estimate used) averaging 1 ha in size. Wyulda squamicaudata fed on leaves of four species of trees (Xanthostemon eucalyptoides X. paradoxus, Eucalyptus spp., and Planchonia careya) as well as the flowers and seeds of a perennial herb (Trachymere didiscordis). Density estimates ranged from 2.3 to 4.6 possums per hectare. This study records the previously unknown occurrence of W. squamicaudata living sympatrically with P. dahli.

I chose the East Alligator region in Kakadu National Park for my study on P. dahli and then proceeded to trial methods of catching the possums. Extensive trapping failed to capture possums as did a tranquilliser gun. I successfully captured possums by hand, anaesthetised them, withdrew blood for biochemical and haematological analysis and fitted adults (n = 4) with radiocollars.

The primary dietary component of Australian ringtail possums is leaves with most species having long intestines that allow them to process low energy, high fibre foods. In contrast, P. dahli has a simple gastrointestinal tract with a short intestine, which suggests that this species may show a low degree of folivory. To investigate this question, I used radiotelemetry (2132 fixes of 13 possums over 3-36 months) and nocturnal observations (280 observations) of feeding behaviour in free ranging possums. Family members denned together in rocks and moved down from rocks to feed in trees growing near the rocks. Possums foraged in cohesive family groups (adult pair and up to two young) and spent eighty five percent of their time foraging in trees within 20 m from rock outcrops. Instead of one plant species dominating the diet of possums, groups ate up to 7 different species. The bulk of the diet included leaves from 22 plant species with some fruits and flowers were also consumed, as was a termite nest. Possums ate leaves of Acacia difficilis, Eucalyptus miniata and leaves and fruit from Termina/ia carpentaria, significantly more often than would be expected
according to their availability. Conversely, possums ate Syzygium suborbiculare and Eucalyptus tetradonta significantly less often than expected based on the availability of these plant species. Possums fed on both mature and young leaves, and only sub-adult possums spent significantly more time feeding in the tops of the canopies than in the middle or lower strata. These results suggest that P. dah/i is a generalist folivore.

To live successfully as a closeknit group, a high level of communication between individuals is expected. To investigate the degree of communication in P. dahli, I made detailed observations of 1 o wild possum groups and opportunistic observations of another 6 groups over three years. Adults of both sexes used olfactory communication via caudal and sternal glands. Both sexes scent-marked rocks, trees (branches and trunks) and termite mounds. In addition, I observed a total of 37 individual olfaction acts directed towards the nose, buccal, rump and chest regions and none towards the pouch or cloaca regions. Possum vocalisations were complex and were made by all group members, however these were not heard often. Olfactory communication occuring extensively and vocalisations used at low frequency suggests olfaction to be more important than vocalisation in communication of P. dahli.

Date of Award	2002
Original language	English
Supervisor	Greg Hill (Supervisor)