Habitat features critical to the survival of the western barred bandicoot include areas of dense ground cover to avoid predators, with leaf litter for constructing nests, and a minimum of introduced predators.
Habitat features critical to the survival of the burrowing bettong include areas of open habitat with some ground cover and soil suitable for warren construction. It was thought that foxes need to be absent and feral cats controlled to low levels (Short and Turner 2000); however, the recent loss of the majority of the reintroduced population of burrowing bettongs at Heirisson Prong in the presence of feral cats (Short unpublished data), suggests that both foxes and cats need to be eradicated completely.
Habitat features critical to the survival of the banded hare-wallaby include areas of dense heath and shrub thickets to avoid predators. Sites that might have suitable habitat include: Faure Island, Peron Peninsula and Edel Land in Shark Bay, and conservation reserves in the south coastal region of WA. However, banded hare-wallabies are unlikely to persist at sites where introduced predators are present (Hardman, 2006).
Habitat critical for all three threatened Shark Bay marsupials includes:
existing habitat of wild populations: all habitat on Bernier and Dorre (western barred bandicoot, burrowing bettong and banded hare-wallaby), and all habitat on Boodie and Barrow Islands (burrowing bettong)
potential habitats that present opportunities for reintroduction of one or more of these species: sites that have been managed for the conservation of threatened species for a number of years: Heirisson Prong, Peron Peninsula, Dryandra Woodland, Faure Island, Lorna Glen, Yookamurra and Scotia WS and the ARR
All these conservation sites have programs to control introduced predators, represent locations within the past range of all or some of the western barred bandicoot, burrowing bettong and banded hare-wallaby, and either have reintroduced, or have plans to reintroduce one or more of these three species. At all these sites, and any others to be considered in the future, the control of introduced predators is a necessity, and management to ensure adequate vegetative cover is important.
3.5 Important populations
Important populations of western barred bandicoot, burrowing bettong and banded hare-wallaby include:
All wild populations (on Bernier, Dorre, Barrow and Boodie Islands)
All reintroduced populations. Populations of western barred bandicoots, burrowing bettongs and banded hare-wallabies on Faure Island Wildlife Sanctuary are of particular importance due to the eradication of introduced predators and the low likelihood of re-invasion due to its island status. Reintroduced populations on Heirisson Prong, the Arid Recovery Reserve and Faure Island all appear to be doing well and are therefore significantly important to the continued conservation efforts for burrowing bettongs.
The reintroduction of burrowing bettongs to Lorna Glen (January 2010-) is in its infancy but may prove important in time.
Captive populations, to provide animals for reintroduction programs (to supplement the use of animals from the wild populations) and for public education.
There have been a common series of threats to the former mainland populations of the western barred bandicoot, burrowing bettong and banded hare-wallaby and many other threatened native mammal species. These include predation by the introduced fox and feral cat, habitat alteration by rabbits, livestock and clearing, and changes in fire regimes. Many of these threats remain on the mainland. The major threats to the Shark Bay islands populations of the western barred bandicoot, burrowing bettong and banded hare-wallaby and their habitats, outlined in the Shark Bay Terrestrial Reserves Management Plan 2000-2009 (Hancock et al. 2000) and equally applicable to Barrow and Boodie Islands are:
the introduction of exotic predators (foxes and feral cats);
the introduction of mammalian herbivores (rabbits, sheep, cattle, horses, goats);
a major fire event;
inappropriate recreation activity, development or management practices, and
effects from climate change, particularly reduced rainfall and increased wildfires.
These threats are potentially of similar significance to the reintroduced populations, and disease and wildfire are significant potential threats to captive populations.
European foxes and cats are absent from Bernier, Dorre, Barrow, Boodie and Faure Islands. They are present across mainland Australia, apart from fenced areas within where foxes have been eradicated (foxes) or controlled (cats at some sites).
Foxes have long been recognised as a threat to native wildlife (e.g. Le Souef and Burrell 1926; Finlayson 1961) and are known to predate on native mammals such as the burrowing bettong (Short et al. 2002), and the western barred bandicoot (Finlayson 1961). Cats also consume a wide variety of native mammals, and have been found to consume bandicoots and bettongs when available (Dufty 1991; Christensen and Burrows 1994; Short and Turner 2000).
Burbidge and Manly (2002) found that the presence of both foxes and cats were correlated with the extinction of critical weight range mammals on Australian islands, but cats were associated with extinctions on the more arid islands only. Extinctions of mammals on arid islands with cats but no foxes include Dirk Hartog, Hermite, Trimouille, St Francis and Reevesby Islands (Burbidge and Manly 2002). Both the reintroduced and the wild threatened mammal populations on Bernier, Dorre, Faure, Barrow and Boodie Islands are extremely vulnerable to the introduction of feral cats.
Although Flannery (2003) has suggested that cats may not have been responsible for the extinction of any species in the Australian environment, a number of threatened mammal reintroductions have failed in the arid zone due primarily to predation by cats (e.g. Short et al. 1992; Gibson et al. 1994; Christensen and Burrows 1994; Southgate 1994; Morris et al. 2004; Hardman 2006). Reintroductions to the Gibson Desert in 1992 and to Yookamurra Wildlife Sanctuary in SA in 1995, 1996, 2001 and 2004 were thought to have failed because of predation by feral cats (Christensen and Burrows 1994), predation by cats and foxes (J. Bentley11 pers. comm.) and possibly poor habitat quality (Short and Turner 2000). Cats were the primary cause of the failed brushtailed bettong (or woylie; Bettongia penicillata ogilbyi) translocation to Nature Reserve (in Western NSW) (Priddel and Wheeler 2004). Predation by cats and foxes is considered the main reason for the decline to extinction on mainland and/or as a threat to western barred bandicoot, by Maxwell et al. (1996), Richards and Short (2003), and Richards (2004) and for burrowing bettong on mainland Australia (Short 1998; Short and Turner 2000).
Many studies have highlighted the detrimental impact of introduced herbivores (rabbits, sheep, cattle, horses, goats) on the Australian environment (e.g. Rolls 1969; Foran 1986; Payne et al. 1987; Friedel et al. 1990). Morton (1990) suggested that introduced herbivores, in particular the rabbit, played a significant role in the decline of mammals from the arid and semi-arid zone of Australia. He suggested that introduced herbivores had altered the vegetation so that refuge areas during periods of drought were no longer available. This habitat degradation, combined with the impact of introduced predators and changes in fire regimes in some areas, was thought to have increased the risk of local extinctions of native mammals.
Various authors (Finlayson 1958; Newsome 1971; Burbidge and McKenzie 1989) have attributed the extinction of the burrowing bettong from mainland Australia to competition by rabbits during periods of drought. However, Robley et al. (2002), Richards and Short (2003) and Richards (2004) have demonstrated that the impacts of rabbits on reintroduced populations of burrowing bettongs and western barred bandicoots at Heirisson Prong were minimal, and did not appear to affect the ability of these species to reproduce and establish a population at this site. Burrowing bettongs coexisted with rabbits in the same warren for some time in SA (Copley et al. 2003). There is no information available about interactions between banded hare-wallabies and rabbits. Despite these observations, where possible, rabbits should be controlled or eradicated to facilitate recreating original habitats, and avoid the potential for interspecific competition.
Other introduced herbivores, including livestock (camels, goats, cattle, pigs, sheep and donkeys) have been implicated in widespread habitat alteration (Rolls 1969); however, their distributions are no longer sympatric, with the exception of the limited low density population of feral goats on Peron Peninsula. While there is some doubt that banded hare-wallabies occurred on Dirk Hartog Island (Baynes 1990), Shortridge (1909, p. 818) noted that “in the south of Dirk Hartog Island there is a large sheep station and the wallabies are said to have entirely left that end of the island”. Their suggested extinction from the island around 1920 was thought to be due to predation by feral cats (Burbidge and George 1978), and an attempt to reintroduce (or introduce) the species in 1974 failed, probably due to a combination of predation by cats, a period of summer drought, and the impact of grazing by livestock (Short and Turner 1992).
A small infestation of buffel grass (Cenchrus ciliaris) is on Bernier Island. This is not considered a threat because of the small extent and limited ability for the current infestation to spread as it is currently being managed through herbicide application. Biosecurity measures are in place to prevent further introductions of other weeds.
The potential for the introduction of disease by humans within the threatened Shark Bay marsupial populations was listed as a threat by Hancock et al. (2000). In May 2000 symptoms of two diseases in the western barred bandicoot population on Bernier Island, and captive populations at Peron Peninsula, Kanyana, RTDBF, Monarto Zoo and the ARR (though no signs have been evident in the released population) were discovered. One of the conditions is a papilloma-like syndrome, which has no effective treatment, and has resulted in the death or euthanasia of over 20 animals from captive colonies at Kanyana and the PCBC. The papilloma-like syndrome was also found in a single individual within the captive population at Dryandra as recently as 2006. However, this disease is thought to have evolved naturally in the population and is species specific (Bennett et al. 2008; Woolford et al. 2007; Woolford et al. 2008). It has been managed at the captive breeding facilities by separating breeding stock. The Heirisson Prong population is presumed “disease-free”. Examinations of >20 animals on Bernier Island by DEC in 2002 and by Murdoch University in 2005 found no evidence of the syndrome. The disease is most often seen in older animals that have already reproduced and therefore it is not considered a major threat.
The second involves ocular disease associated with isolation of Chlamydia. Investigation of wild populations on Bernier Island resulted in the discovery of a low level of positive Chlamydia (of several different types) in both ocular and urogenital samples, but not necessarily associated with clinical disease. Sims results (2002) suggested that the papilloma-like syndrome might have been introduced as a result of human activity on the islands, although recent examination of museum specimens only has identified the presence of the disease in Bernier Island animals since at least 1982 (Woolford et al. 2008). In contrast Chlamydia is known to be transmissible between people and fauna such as western barred bandicoots that are animal hosts (Kutlin et al. 2007). The potential risk of transmission from humans to fauna and vice versa should be considered along with other diseases, under the “disease risk management strategy”, and human visitation to the islands regulated with this in mind.
The extent of the threat of disease is thought to be minimal and manageable; however, diseases in native wildlife can contribute to poor population health, and reduced fertility. Extinctions caused by disease are often difficult to diagnose, as diseases do not usually leave conspicuous numbers of dead and dying animals (Caughley and Gunn 1996). There is currently no evidence that the papilloma-like syndrome is transmissible between native species.
Toxoplasmosis is an infectious disease caused by the one-celled protozoan parasite Toxoplasma gondii. Cats are the only known definitive hosts of this parasite (Johnson et al. (1988), which is common in marsupials as both a subclinical infection and an overt disease (Munday 1978). For example, toxoplasmosis is prevalent in wild populations of eastern barred bandicoots (Obendorf and Munday 1990), and macropods in SA (Johnson et al. 1988). The disease has caused the death of western barred bandicoots in captivity at Kanyana Wildlife Rehabilitation Centre (J. Butcher12, pers. comm.). Dickman (1996) suggested that declining populations of native wildlife should be screened to determine whether toxoplasmosis currently has serious deleterious effects. Research has suggested that toxoplasmosis is not prevalent in the native mammal fauna of Shark Bay (P. Adams13, pers. comm.).
Hardman (2006) found three endoparasite species (Strongyloides sp., Entamoeba sp. and Eimeria sp.) in banded hare-wallabies reintroduced to Peron Peninsula in winter and spring, though animals appeared free of the parasites during summer and autumn. No ectoparasites were found.
Bernier Island has no documented history of burning; however, substantial portions of Dorre Island were burnt in 1860, 1909 and 1973 (Ride et al. 1962; Hopkins and Harvey 1989; Hancock et al. 2000). Fires have therefore been infrequent in the last hundred years. The persistence of banded hare-wallabies on Bernier and Dorre Islands, with their very different fire histories, the infrequent nature of fire in the region, and the lack of introduced predators, suggests that a fire mosaic is not important on islands (Short and Turner 1992; I. Abbott14 pers. comm.). Fire issues may be important at sites such as Dryandra Woodland, Lorna Glen and Scotia WS; however, DEC and AWC have implemented fire management regimes in these areas.
Fire may substantially reduce population size in the short term, but in the long term, populations are likely to maintain their ability to recover, in a fashion similar to recovery from drought (Short et al. 1997a).
Fire may play a significant role in reducing cover and exposing animals to predation, particularly banded hare-wallabies that rely on dense cover for shelter and are consumed by wedge-tailed eagles (Richards and Short 1998), and western barred bandicoots that rely on litter for the construction of nests.
Burbidge et al. (1988) suggested a possible link with the disappearance of critical weight range mammals from the central deserts and the timing of Aborigines departing from the region, resulting in a change in fire regimes.
The threat of inappropriate recreational activities, development, or management practices on either the wild or reintroduced populations of the western barred bandicoot, burrowing bettong and banded hare-wallaby is minimised under current management guidelines (see section 4.1 Prior and existing conservation measures). Recreational and tourism activities tend to be permitted and managed in the Shark Bay region in a “manner compatible with conservation and other goals,” to minimise environmental impact (Hancock et al. 2000, p. 39) but this doesn’t stop fishermen and day trippers from lighting fires which potentially could get out of control. Recreational activities such as fishing, camping and picnicking are permitted on Heirisson Prong (Short 1999b), where burrowing bettongs have been reintroduced.
Hancock et al. (2000) regarded any permanent structures such as island-based tourism facilities (e.g. jetties, airstrips, accommodation) as incompatible with the high conservation values of Bernier and Dorre Islands. Barrow Island has a history of industrial development, with the establishment of an oilfield in 1964 by West Australian Petroleum Limited. Development is continuing with the expansion by Chevron and Joint Venturers (Gorgon Development). While subject to a rigorous Environmental Management System and Quarantine Risk and Management Strategy (Chevron Australia 2005), this minimises, but does not preclude, detrimental effects upon native mammals and their habitat, particularly introduction of exotic species such as the black rat Rattus rattus and house mouse Mus musculus.
Developments at reintroduction sites such as François Peron National Park may be compatible with community participation, ecotourism and public education where appropriate actions are taken to minimise environmental impacts. A successful example is ‘Barna Mia’, the native animal viewing enclosure that has been constructed at Dryandra Woodland by DEC, where the general public are able to see burrowing bettongs, bilbies, woylies and quenda (Isoodon obesulus fusciventer).
Climate change will result in a range of effects that will bring further uncertainty to management of these species. Specific threats to these species resulting from climate change effects may be declining annual rainfall and increased frequency of extreme weather events (high temperatures and storms) and associated increase risk of fire. Severe drought is known to affect all species covered in this recovery plan. Recent data from 2006-2010 showed reduced numbers of each of the species on Bernier and Dorre Islands, particularly the western barred bandicoot, following periods of low rainfall (Figure 5).
Figure 5: Global population estimates for Bernier and Dorre Island a) western barred bandicoot b) burrowing bettong and c) banded hare wallaby, with average rainfall trends included.