The ecology of the Northern Quoll, Dasyurus hallucatus

Abstract

The ecology of the Northern Quoll (Dasyurus hallucatus) was studied at Kapalga Research Station in Kakadu National Park, Northern Territory between August 1992 and May 1995. D. hallucatus is a nocturnal carnivorous marsupial (Dasyuridae) which is sexually dimorphic with the males weighing on average 760g (maximum 1120g) and the females 460g. Since European settlement in Australia, this species has declined from a broad band across northern Australia to several disjunct populations. Most of the decline has occurred in the extensive lowland savanna habitat, leaving remnant populations in dissected rocky plateaux such as Carnarvon Gorge (Qld) and the north-west Kimberley region (WA). This study was conducted in lowland savanna, where the continued survival of D. hallucatus populations appears to be the most tenuous. The aims were to investigate the life history and ecological requirements of the species to elucidate possible reasons for decline. D. hallucatus was opportunistic in den use, using mainly hollows in trees, rock crevices, and logs but also termite mounds and burrows in accordance with availability. Females used rock crevices more often than males, whereas males used logs more often. Each individual used many dens and shifted every night. Individuals of both sexes denned solitarily. Diet was also opportunistic. D. hallucatus was omnivorous, virtually always including insects in the diet but also consuming a wide range of vertebrates and fleshy fruits when they were most abundant. Plant consumption peaked in the late-wet to early dry season (March-April), vertebrate consumption peaked in the mid-dry season (July-August) and invertebrate consumption peaked during the late-dry to wet season (September-February). Both sexes showed a similar pattern of seasonal variation. However, females consumed less vertebrates than males during May-June in one year. Juvenile weaning and dispersal coincided with the wet season, when invertebrates were most prevalent. There was no difference detected between adult and juvenile diet. D. hallucatus appears to forage predominantly on the ground and suitable prey was present in all habitats in the study area (open forest, woodland, rocky hills and riparian). D. hallucatus exhibited a highly synchronous breeding cycle. Within the study population in a given year, there was little variation in the timing of reproductive events, with the onset of each event usually occurring within a week for all individuals. Mating occurred late May/early June each year. Males at this site demonstrated complete post-mating mortality, consequently adult males were totally absent from the Kapalga study site from September-October each year. Since weight was an unreliable indicator of age, it is possible that males in all previously studied D. hallucatus populations may also breed only once. Male mortality may have a similar aetiology to die-off in the semelparous Antechinus species. Males become anaemic, infested with ectoparasites and lose condition and weight. However, unlike Antechinus spp., there was no evidence that ulceration caused the anaemia in D. hallucatus. Additionally, D. hallucatus testes did not senesce, so males could be capable of breeding again if they survived to a second mating season. Perhaps this species is an example of the evolution of semelparity in progress. For a species of this body size, D. hallucatus has a remarkably short lifespan with all males and most females only surviving for a single breeding season. The maximum recorded age for wild males was 17 months and for females, 37 months. A single litter of 5-8 young attached to each female's teats in mid-late June. Litters of first year females were predominantly male, whereas litters of older females were female-biased. Crown-rump length increased linearly with respect to time from 0-60 days after birth. The young remained in the pouch for about 9 weeks and were deposited in nursery dens in mid-late August. During the nursery period, females used more termite mounds and less log dens than during the rest of the year. It is likely that the young were not fully capable of thermoregulation when first deposited in dens since the mothers built simple nests of dry leaves and grass during the first four weeks after deposition. Unlike other Dasyurus species _which use one nursery den, D. hallucatus mothers shifted the juveniles to different nursery dens every few nights, although shifting less often than during the rest of the year. Mothers did not forage when moving the young to a new den. Mothers stayed with their young in the den during the day. Each night, mothers would leave to forage and generally returned once or twice during the night for an average of 50 minutes each visit during the early nursery denning period decreasing to 30 minutes in the late nursery period. Adult and juvenile scats were observed deposited at den entrances mainly during October-November, just before the young became independent. This may be for hygiene, or as a signal to assist the young relocate the nursery den after their first foraging forays. Weaning was gradual, beginning in late October and ending mid-December. The young dispersed in December-February, at an age of 6-8 months. The mean distance between successive dens of resident females was at its maximum at this time, this may be to assert their occupancy of an area by monitoring and scent-marking. Female D. hallucatus appeared to be territorial with essentially nonoverlapping denning areas and a home range of about 35 hectares. Male home range may be similar in size to females prior to the mating season, but expanded during the mating season to over 100 hectares, overlapping with several female ranges and with numerous other male ranges. Males were found in all habitats whereas females preferred rocky hills. During the mating period, males adopted a roving strategy, regularly visiting several distant females in rapid succession, presumably to monitor the onset of oestrus. Females were visited by several males. This intense physical effort by males during the mating period is likely to be a major contributor to their physiological decline and subsequent die-off after the mating period. The marked sexual dimorphism of D. hallucatus may be the result of selection for larger, wider ranging males in a promiscuous mating system and for energetically more efficient smaller females, as females rear the young alone. There was no evidence that toxoplasmosis or any other disease was a major contributor to Northern Quoll decline in this region. The main proximate cause of mortality for both sexes was predation by dingoes, cats, snakes and an owl. Large numbers of males were also killed by motor vehicles during their extensive travels during the mating period. Most females died during the late dry season, after fires (which burn 55% of lowland savanna in Kakadu each year) have removed much of the ground cover. Rocky habitat appeared to be preferred by females and those occupying this habitat were more likely to survive to a second breeding season. No instances of predation of Northern Quolls were recorded on the rocky hills, this may be due to a greater number of refuge sites or lower predator presence. It is suggested that the decline of D. hallucatus in lowland savanna may follow land management practices (such as extensive fire, grazing and clearing) that increase the vulnerability of D. hallucatus to predators. Show more