The northern quoll (Dasyurus hallucatus) is the smallest of the four quoll species endemic to Australia, and has suffered significant recent declines due to the spread of a number of threatening processes including ingestion of the toxic cane toad, altered fire regimes, and habitat loss and modification. In many areas, the species has survived by persisting in rocky country but populations are fragmented and isolated. In the recent mining boom of Western Australia many areas where the northern quoll has persisted were targeted for mining, and there have been an increasing number of mining projects needing to manage and mitigate impacts to populations of this species. There are also a number of conservation initiatives in progress that aim to buffer the northern quoll from the continuing threat of exotic species and habitat modification. However, the northern quoll is a cryptic species that occurs in remote areas and research to date has been limited by logistic constraints and sampling difficulty. On Koolan Island, the northern quoll has persisted despite a long history of mining for iron ore (1934 – 1940; 1965 - 1993; 2006 - present). Therefore, this thesis aimed to study the ecology of Koolan Island northern quolls to better understand the population dynamics, diet and habitat use of an island population, and examine any interactions with modified areas.
Fieldwork undertaken between 2014 and 2017 on Koolan Island was combined with a mark-recapture dataset spanning 13 years (2006 - 2018). The dataset was analysed using both spatial and non-spatial capture recapture methods to examine the population dynamics of northern quolls on Koolan Island. Using both methods aided in circumventing the analytical constraints of the study design, which was typical of many long-term monitoring programs in that it was spatially inconsistent (trap location varied) between years. Females were rarely captured between years, with no male recaptures suggesting a near-complete male die-off before the next breeding season. Apart from a decline in 2010-2011 following a cyclone, the population remained relatively stable and was not in continuous decline between 2006-2018 (~12.65 individuals/ km2). Using estimates of seniority (the probability that an individual present in year t was also present in year t – 1), recruitment was found to drive population change (seniority = 0.18; 95% CI 0.12–0.27).
Dietary analysis was conducted using scats collected across the island from 2014 - 2017, with a total 448 scats from both anthropogenic and native habitat types. Closed capture models were used to examine differences in diet between anthropogenic and native habitat to contrast the wet and dry season, and Fisher’s Exact Tests were used to determine if prey were consumed relative to their availability. A total of 32 food items were detected in the northern quoll diet, with the most commonly consumed foods including invertebrates (beetles/cockroaches, crickets/grasshoppers, centipedes, crustaceans), skinks, and major fruiting plants found on the island (Ficus sp. and fruit of the stinking passionflower Passiflora foetida). Closed capture analysis indicated that diet composition was influenced by both season and habitat type. Invertebrates were the most commonly consumed food type by far, in particular beetles/cockroaches which were consumed more often than would be expected based on their availability in the environment (P < 0.001). Fruits were consumed in moderate amounts (found in 43.1% of scats), and vertebrates were consumed the least in both modified and unmodified habitats and across seasons.
Given population dynamics are driven by recruitment, juvenile survival is likely to be critical to the persistence of the northern quoll. The northern quoll is dependent on its mother for the first stage of life, and young are deposited in dens while the female forages at night. Therefore, this thesis also investigated the characteristics of dens selected by females during the young in den phase to better understand den attributes that may influence selection by this species. A total of 22 dens were located by tracking females captured in both anthropogenic and native habitats. The structural and habitat attributes of these dens were compared with similar available ‘dens’ in the surrounding area using logistic regression. Temperature and humidity of used dens (n = 22), available dens (n = 24) and ambient sites (n = 12) were also measured to determine the microclimatic properties of selected dens. Dens were found in trees (n = 4), rock crevices (n = 12), and underground (n = 6), with no dens found in anthropogenic areas. One den was located in an area with commenced but not complete rehabilitation (earthworks undertaken). Using generalised additive mixed models (GAMM), used dens appeared to provide a more stable temperature and humidity throughout the day than both available den sites and ambient conditions. Rocky dens had more stable microclimates than dens in trees or earth. Aerial cover (canopy and/or rocky cover) and number of entrances best predicted female den selection during the young in den period.
Overall, my findings indicate that northern quolls on Koolan Island currently exist in a stable population and take advantage of certain resources available in modified areas, appearing relatively resilient to the anthropogenic habitat modification that has occurred to date. Of particular interest is their use of the stinking passionflower, which is the subject of weed control programs on the island. The high level of invertebrate consumption across seasons and habitats, particularly beetles and cockroaches, indicates the importance of this food item to island populations. Low vertebrate consumption may be due to prey availability on the island, or reflect the smaller body size compared to mainland populations. While northern quolls appear to forage in both modified and unmodified environments, maternal den use seems heavily reliant on native habitat, indicating that suitable denning habitat in undisturbed areas must be preserved for a population to persist. Denning habitats that provide a stable microclimate, aerial cover and multiple entry/exit points are likely to be preferred by females during the young in den period and may support juvenile survival at a critical life stage. Collectively, the research detailed in this thesis contains pertinent information on population dynamics, diet, and den site selection to inform conservation efforts across northern Australia and worldwide that target cryptic, rare and endangered mammals
