By Dr Alexander Watson, Regional Ecologist; Dr Gabrielle Beca, Wildlife Ecologist; Dr Tom Sayers, Wildlife Ecologist; Dr Skye Cameron, Regional Ecologist; Dr John Kanowski, Chief Science Officer; Jess Teideman, Science Writer; Joey Clarke, Senior Science Communicator
Australia’s four species of quolls are the largest marsupial carnivores on the mainland. As predators at or near the top of the food chain, they play an outsized role in the ecosystems of which they’re a part and their conservation is considered important for the overall health of ecosystems. Despite their sharp teeth and feisty temperament, they have not fared well since European colonisation. Direct persecution, the impacts of changed fire regimes and the introduction of cats, foxes and cane toads have resulted in all quoll species being threatened with extinction across all or parts of their range. Quolls are in the spotlight of conservation efforts across Australia: Northern, Western and Eastern Quolls are listed as Priority Mammals in the Federal Government’s Threatened Species Action Plan 2022–32. However, while some populations of quolls are confronting new threats, others are making an assisted comeback.
Northern Quolls, the smallest of the four Australian quoll species, are known by many different names across northern Australia (including Barkuma as the Yolgnu People of Arnhem Land know them and Wijingarra in the west Kimberley on Dambimangari Country), where they were once widespread. Their distinctive life history (common across small dasyurids), where males die off annually after breeding, has allowed them to thrive in ecosystems that change dramatically between wet and dry climates on a seasonal basis. This strategy, successful over evolutionary time, was challenged by the introduction of cattle, changed fire management and predation by feral cats following European colonisation. Then further catastrophe struck in the form of a toad. The spread of introduced cane toads across Queensland in the 1930s–90s and, more recently, across the Top End and into the Kimberley, has significantly reduced the distribution of Northern Quolls, with many local extinctions of populations, especially in the more arid and less rocky parts of their range (similar impacts have been experienced by other frog-eating predators, such as goannas and snakes, in the wake of the toad invasion). As a result, Northern Quolls are listed as Endangered.
While it is well known that cane toads have caused a devastating decline in Northern Quolls across most of their range, it is less widely recognised that small populations of Northern Quolls have hung on in areas infested with toads. This includes the western section of AWC’s Brooklyn Wildlife Sanctuary in Queensland. Although the mechanism is still unknown, scientists have observed that these remaining populations are able to coexist with toads, simply by not eating the poisonous invader. Research has also shown that declines in toad-infested areas tend to be in flatter parts of the terrain, with a greater chance that Northern Quolls persist in rocky areas. Differences in survivorship may be due to differences in fire regimes, grazing pressure and cat predation between the relatively protected escarpment country and the flatter, more open savanna woodlands, and perhaps also to differences in toad abundance.
Dens by design
In 2022, AWC began working on an innovative project at Brooklyn to expand the number of areas currently occupied by Northern Quolls. The project has been partly funded by the Australian Government’s Environment Restoration Fund and conducted in collaboration with Western Yalanji Traditional Owners and scientists from Terrain and Gulf Natural Resource Management. Twelve artificial dens were designed and built on the margin of habitats currently occupied by Northern Quolls on Brooklyn. We are waiting until the end of the next wet season (summer 2023–24), when young Northern Quolls are likely to disperse and encounter these artificial homes, to determine whether the artificial dens will assist quolls to extend their range into savanna woodlands on Brooklyn.
In the last 12 months, AWC has also worked closely with Western Yalanji Traditional Owners to undertake fire management on Brooklyn in the vicinity of the artificial dens. These fires are designed to create a mosaic of vegetation at different ages since fire to maintain a balance of fire-stimulated resources and vegetation cover, to help limit feral cat predation. AWC has also been taking genetic samples from Northern Quolls at Brooklyn to better understand what impact recent declines and fragmentation have had on the genetic diversity of remaining populations, which will be central to informing future translocations planned for the species.
The march of the cane toads
The Northern Quoll is a focal species for AWC’s conservation efforts in the Kimberley. Knowing how serious the impacts of toads have been on quoll populations elsewhere, AWC ecologists have been closely monitoring populations of the Northern Quoll before and after the arrival of cane toads as they spread west across the region. At Mornington–Marion Downs Wildlife Sanctuary, AWC ecologists collaborated with external researchers to test and deploy cane toad sausages, laced with a nausea-inducing compound, in an attempt to teach quolls not to eat toads. Unfortunately, that approach didn’t work (see Indigo et al. 2023), so we changed tack at Charnley River–Artesian Range Wildlife Sanctuary, focusing on managing existing threats (such as wildfire and feral animals) in the hope of assisting some quoll populations to survive the invasion of toads.
In the Artesian Range, surveys were conducted in the two wet seasons before toads invaded the area (2018–19, 2019–20) and again in 2020–21 following the arrival of toads. These data revealed a 73% decline in quoll abundance across eight sites after the toad’s arrival. Encouragingly, however, the most recent survey conducted during the 2022–23 wet season confirmed the persistence of Northern Quolls at most survey sites. Further analysis of the data will be conducted to quantify changes in the abundance of the population.
There are several reasons why quolls might be persisting here, in contrast to more drastic declines that have occurred at Mornington and elsewhere in the southern and eastern Kimberley:
Regardless of the reason, the hope now is that remaining quoll populations become more averse to eating toads, for example because ‘toad smart’ individuals are persisting and passing on their genes, or because ‘toad smart’ mothers are passing on toad-aversion behaviours to their young.
AWC ecologists will continue to monitor Northern Quoll populations in the Kimberley, and threats to the persistence of those populations, as part of our Ecohealth Monitoring Program. Data from the program will help inform development of a conservation management plan for the species in the region.
RETURN OF THE CHUDITCH
The Chuditch (Western Quoll) was once one of the most widespread predators in Australia, occupying 70% of the continent, in diverse landscapes ranging from forest to grassland to desert. As with so many of Australia’s small and medium-sized mammals, this species was wiped out from inland Australia after European colonisation and the resultant changes to ecosystems, particularly the introduction of feral predators and changes to fire regimes. The Chuditch is now extinct across 95% of its former range.
In 2023, AWC began the reintroduction of the Chuditch to Mt Gibson Wildlife Sanctuary in Western Australia.
In the first two tranches of the reintroduction, a total of 34 quolls were released at the sanctuary, sourced from two locations in south-west Western Australia. All animals were released outside the 7,800-hectare fenced safe haven, facilitated by an increase in ongoing efforts to control feral cats and foxes. This important reintroduction marked the first time a top-order marsupial carnivore has been restored to a part of its former range by AWC. It follows the successful release of Brushtail Possums outside the fenced area at Mt Gibson in 2021–22.
Monitoring of the quolls will continue for up to 12 months post-release using an advanced drone radio-telemetry system from Wildlife Drones. This new technology enables ecologists to track multiple individuals simultaneously and over large areas, as they settle into the new environment.
The Chuditch is the tenth species AWC has reintroduced to Mt Gibson, setting a new benchmark for reintroduction programs across the country. Plans to introduce quolls inside the fence will be considered once populations of the other reintroduced species have successfully established and grown in numbers, sufficient to tolerate the additional level of predation.
SPOTTING THE POSSIBILITIES
The Spotted-tailed Quoll is the largest of the Australian quoll species. Populations in south-east Australia and North Queensland are listed as Endangered, while the Tasmanian population is listed as Vulnerable.
Research has shown these quolls need large patches of forest with adequate denning resources: areas with relatively high densities of hollow-bearing trees, fallen timber and medium-sized mammalian prey. As a top-order predator and the largest carnivorous marsupial on mainland Australia, the Spotted-tailed Quoll plays an important ecosystem role.
AWC’s Gorton Forest Wildlife Sanctuary in NSW is home to a host of forest-dwelling species and primary vegetation communities of wet and dry sclerophyll forests, providing the perfect habitat for the quoll. Spotted-tailed Quolls are known to occur in the area and there has been a recent sighting of the species on the property. Inventory surveys planned to commence at Gorton Forest in 2023 will provide more information.
AWC will protect quoll habitat at Gorton Forest by maintaining and restoring native vegetation through fire and weed management. Feral predator management, aimed at foxes and cats, will reduce predation on quolls and competition with invasive species.
Across the country, these projects show that while quolls have suffered widespread declines, it’s not too late for some populations to recover, or for new populations to establish.
Read or download this full issue of Wildlife Matters here.