Decline of the Eastern Quoll in Tasmania

Bronwyn Fancourt has spent four years researching the causes of the decline of eastern quoll in Tasmania. The following is a brief summary of the extremely enlightening presentation she gave to the Bruny Island community recently.

The eastern quoll is one of Australia’s few remaining carnivorous marsupials. It belongs to the same family grouping as the Tasmanian devil, antechinus and dunnarts and is a protected species under the Nature Conservation Act 2002. Once present across south-eastern Australia, it is now considered extinct on the mainland. Many factors are thought to be linked with its extinction, including foxes, poisons, cane toads, habitat loss, disease and persecution.

Eastern quolls have also experienced recent dramatic declines (greater than 50% in the 10 years to 2009) across mainland Tasmania with no sign of recovery. The species was recently nominated for listing as endangered under the federalEnvironment Protection and Biodiversity Conservation Act 1999 (EPBC Act).

Quolls are indeed fascinating creatures. They are nocturnal and make nests in burrows under rocks or in fallen logs. They live for three to four years in the wild and breed only once per year, in winter. For the first four months or so they are suckled by their mother in the pouch and later in dens. Numbers increase visibly  in summer when the juveniles first emerge. However, the juveniles are particularly vulnerable to predation and, as summer progresses, their numbers gradually decrease.

The quoll’s diet consists mainly of insects, along with rodents, rabbits, lizards and small mammals; they also scavenge on dead animals. They eat many of the species that humans want to manage, such as agricultural pests (e.g. cockchafer beetles, corbie grubs), rodents and rabbits. Quolls like cold dry conditions with minimum winter temperatures around 0oC.

Bronwyn’s research investigated the impacts of climate, the decline in devil numbers, disease (toxoplasmosis) and feral cats on the numbers of quolls at several sites across the state. Her research provided much insight into the ecology and behaviour of the eastern quoll and the interactions between devils, quolls and feral cats. It is indeed a very complex story.  

She found that numbers of eastern quolls declined significantly across Tasmania (including on Bruny Island) during a period of unfavourable weather conditions (i.e. more episodic rainfall combined with warmer early winter temperatures) in the early 2000s. However unexpectedly, the abundance of quolls did not recover despite a return to more suitable weather conditions from 2004. So other factors had to be contributing to their failure to recover.

Bronwyn examined whether the decline in the Tasmanian devil across the state (due to the devil facial tumour disease) may have allowed cat numbers to increase and thus increased predation of quolls by feral cats.  Interestingly, she found no evidence to suggest that the reduction in devil numbers has resulted in an increase in feral cats. However, in areas of the state where devil numbers have been declining for the longest, feral cats were found to be more active during the night. This suggests that they have less need to avoid devils and greater potential to predate on nocturnal animals.

Toxoplasmosis is a disease spread by cats that can be fatal to many marsupials, such as bandicoots, pademelons, wallabies and wombats. Bronwyn’s research found no evidence that toxoplasmosis contributed to the population decline of eastern quolls, nor that it affects their long-term survival. The higher prevalence of toxoplasmosis in some quoll populations across that state indicates a greater exposure to feral cats and thus a higher likelihood that quolls will contract the disease. The quolls on North Bruny had a significantly lower prevalence of toxoplasmosis (9.4 – 29.4%) compared with mainland Tasmanian quolls (77.3 – 100%), indicating less exposure to cats.

She therefore suggested that predation, competition or exclusion by feral cats may be preventing quolls from recovering. Her research found that feral cats and quolls use the same areas and no evidence that the activity or abundance of quolls is affected by the presence or abundance of cats. However a difference in feral cat activity between seasons was observed – cats become more active at night over summer when many vulnerable juvenile quolls are present.

Bronwyn concluded that unfavourable weather conditions in the early 2000s contributed to the initial dramatic decline of the eastern quoll across Tasmania, and that their numbers have fallen below a critical threshold. Thus, faced with ongoing predation pressure, particularly of juvenile quolls by feral cats, their numbers on mainland Tasmania are too small to recover without assistance.

North Bruny, however is an interesting case study – it is one of the few sites across Tasmania where quoll numbers have increased in recent years.  With its favourable climate and mosaic of open grasslands, woodlands and agricultural pastures, it offers ideal quoll habitat. An increase in abundance is possibly due to improvements in pasture management that now provide better quality feeding and denning habitat.

On North Bruny feral cat numbers are also low compared with other parts of Tasmania (including South Bruny). The Neck (a sandy isthmus) likely acts as a barrier to the movement of cats and quolls between the north and south. In addition, regular trapping of feral cats by Parks and Wildlife Service at the Neck Game Reserve (over many years) and the shooting of feral cats on North Bruny may be preventing the movement of cats from the south to the north. 

Several residents with long family links on North Bruny report that the eastern quoll was introduced in the 1970s. While we may never know just how long they have been on the island, genetic studies of their DNA indicate their long-term presence (perhaps from when the channel formed). In addition, reference to numerous quolls on Bruny Island in a 1908 Mercury newspaper supports this, although perhaps historically, their numbers fluctuated, or were in much lower densities. Anecdotal accounts also indicate that quolls have historically lived closely with humans, denning in farm sheds and under buildings. With more dwellings and agricultural buildings and loss of habitat (such as fallen logs) it may be that this behaviour has become more common across Tasmania.

Bronwyn warned that as an island population, eastern quolls on Bruny Island are very vulnerable to unpredictable events, such as climatic changes (e.g. wetter and warmer conditions) or disease outbreaks. In addition, if the number of feral cats increased significantly on North Bruny their predation on juvenile quolls could reduce the quoll population, particularly if combined with other unfavourable events.

Bronwyn recommends that an insurance population (or captive breeding) of quolls be established to supplement other quoll populations across mainland Tasmania.

Kaylene Allan Cat Management Officer, Kingborough Council