title: Behaviour and ecology of tropical rock-possums
title: the rock-haunting possum, Petropseudes dahli and the scaly-tailed possum, Wyuld squamicaudata
titleType: Subtitle
Creators: name: Runcie, Myfanwy
Publisher: name: Charles Darwin University
Year: 2002

description: 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. 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. dahliwith 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 II 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. Wyu/da 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 Ill 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 Terminaiia 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 dahli 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 10 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. 111 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. IV Groups of P. dahli interspersed their activities prior to and during foraging with vigilant behaviour. I used scan sampling to investigate the level of coordination of vigilance within free ranging possum groups. Rockhaunting possums displayed both cooperative sentinel behaviour and synchronous group vigilance. To examine the effects of predators on vigilant behaviour, I compared the duration of vigilant behaviour between possum groups with high and low rates of dingo visitation and between groups with and without young. Both sexes displayed similar rates as sentinels (T = 0.76, df = 7, P = 0.47) however, during synchronous scanning males spent 81% more time solo alert than did females. Possums displayed similar rates of vigilance regardless of the presence of young (or of regions showing evidence of recent dingo presence. Petrospeudes dahli live in family groups consisting of an adult female and male with up to two offspring from different seasons. Males remain with the female all year round suggesting a monogamous mating system. To investigate the question of where P. dahli fits on the monogamy-polygyny continuum, I used radio-tracking to determine home rangeshape and size and observations to measure the degree of symmetry between the sexes in maintaining the pair bond and initiating group activity changes. I also measured the extent of maternal and paternal indirect and direct care. Six possum groups maintained non-overlapping home ranges with long-term consorts and young sharing dens. Males contributed more than females in maintaining the pair bond (F 1t3 = 85.04, P &lt; 0.05) but both sexes contributed equally with parental care either direct care (Fi,3 = 0.17, NS) or indirect care (ANOVA: Fii3 = 0.002, NS). For the first time, the parental behaviours of IV Groups of P. dahli interspersed their activities prior to and during foraging with vigilant behaviour. I used scan sampling to investigate the level of coordination of vigilance within free ranging possum groups. Rockhaunting possums displayed both cooperative sentinel behaviour and synchronous group vigilance. To examine the effects of predators on vigilant behaviour, I compared the duration of vigilant behaviour between possum groups with high and low rates of dingo visitation and between groups with and without young. Both sexes displayed similar rates as sentinels (T= 0._76, df = 7, P = 0.47) however, during synchronous scanning males spent 81% more time solo alert than did females. Possums displayed similar rates of vigilance regardless of the presence of young (or of regions showing evidence of recent dingo presence. Petrospeudes .dahli live in family groups conslsting of an adult female and male with up to two offspring from different seasons. Males remain with the female all year round suggesting a monogamous mating system. To - investigate the question of where P. dahli fits on the monogamy-polygyny continuum, I used radio-tracking to determine home rangeshape and size and observations to measure the degree of symmetry between the sexes in maintaining the pair bond and initiating group activity changes. I also measured the extent of maternal and paternal indirect and direct care. Six possum groups maintained non-overlapping home ranges with long-term consorts and young sharing dens. Males contributed more than females in maintaining the pair bond (F 1,3 = 85.04, P &lt; 0.05) but both sexes contributed equally with parental care either direct care (F1,3 = 0.17, NS) or indirect care (ANOVA: F1,3 = 0.002, NS). For the first time, the parental behaviours of V bridge formation, embracing, marshalling of young, sentinel behaviour and tail beating have been reported in a marsupial. Males participated to a high degree in maintaining relationships with one mate and their offspring. These results suggest that this P. dahli population has obligate social monogamy. My studies on a wild population of P. dahli show that this highly social species has an extensive communication system and well coordinated antipredator behaviours. In contrast, W. squamicaudata appears to be solitary with a much less developed social system. In some areas they are sympatric and probably compete for food and den resources. To investigate whether P. dahli is restricted to certain habitat types I recorded environmental and floristic variables along 50 transects spread from the Kimberley region in in the west to East Arnhem land in the north, to the Gulf of Carpentaria in the south and sites in between. At each site I recorded details of a range of environmental variables. I used logistic regression to see whether any of the habitat structural variables predicted the presence of P. dahli.' This analysis revealed that P. dahli is associated with burnt sites where rock outcrop lengths are &lt; 1 km. The sites where P. dahli is most likely to occur are rock isolates which may be particularly vulnerable to anthropogenic disturbances. Since European settlement, land use changes have occurred across much of northern Australia. For example, in the east and west Kimberley region where W. squamicaudata is thought to be extinct, pastoralism has greatly altered vegetation and fire regimes have changed. Similarly, many of the rock outcrops inhabited by P. dahli are currently influenced by these altered landuse practices. Pastoralism and altered fire regimes are V bridge formation, embracing, marshalling of young, sentinel behaviour and tail beating have been reported in a marsupial. Males participated to a high degree in maintaining relationships with one mate and their offspring. These results suggest that this P. dahli population has obligate social monogamy. My studies on a wild population of P. dahli show that this highly social I species has an extensive communication system and well coordinated antipredator behaviours. In contrast, W squamicaudata appears to be solitary with a much less developed social system. In some areas they are sympatric and probably compete for food and den resources. To investigate whether P. dahli is restricted to certain habitat types I recorded environmental and floristic variables along 50 transects spread from the Kimberley region in in the west to East Arnhem land in the north, to the Gulf of Carpentaria in the south and sites in between. At each site I recorded details of a range of environmental variables. I used logistic regression to see whether any of the habitat structural variables predicted the presence of P. dahli. - This analysis revealed that P. dahli is associated with burnt sites where rock outcrop lengths are&lt; 1 km. The sites where P. dahli is most likely to occur are rock isolates which may be particularly vulnerable to anthropogenic disturbances. Since European settlement, land use changes have occurred across much of northern Australia. For example, in the east and west Kimberley region where W. squamicaudata is thought to be extinct, pastoralism has greatly altered vegetation and fire regimes have changed. Similarly, many of the rock outcrops inhabited by P. dahli are currently influenced by these altered landuse practices. Pastoralism and altered fire regimes are VI suspected as causes for biodiversity decline across northern rocky regions. Both of these processes influence native vegetation and as rock-possums require a variety of plant species in their diet, maintaining floristic diversity is important for their conservation. Thus, management strategies should be aimed at' maintaining high floristic diversity on existing rock-possum habitat or at least maintaining those food tree species selected for by possums. Three ways to achieve this are by: (i) lighting low intensity fires biennially or annually; (ii) conserving monsoon forests to protect avian seed dispersers that contribute to the seed stock of many rock outcrops; and (iii) constructing fences more than 20 m from rock outcrops to eliminate grazing by stock and feral animals (goats, horses etc). Finally, we need long term monitoring of existing populations. Without such programs we will not know the rates or causes of range contraction, which threatens these marsupials of conservation significance. VI suspected as causes for biodiversity decline across northern rocky regions. Both of these processes influence native vegetation and as rock-possums require a variety of plant species in their diet, maintaining floristic diversity is important for their conservation. Thus, management strategies should be aimed at' maintaining high floristic diversity on existing rock-possum habitat or at least maintaining those food tree species selected for by possums. Three ways to achieve this are by: (i) lighting low intensity fires biennially or annually; (ii) conserving monsoon forests to protect avian seed dispersers that contribute to the seed stock of many rock outcrops; and (iii) constructing fences more than 20 m from rock outcrops to eliminate grazing by stock and feral animals (goats, horses etc). Finally, we need long term monitoring of existing populations. Without such programs we will not know the rates or causes of range contraction, which threatens these marsupials of conservation significance. Preface In Australia, extensive clearing of the native vegetation over the past 200