3.1 Western barred bandicoot Perameles bougainville
Taxonomy and description
The western barred bandicoot was first described from a specimen taken at Peron Peninsula in Shark Bay (Figure 1) by naturalists Quoy and Gaimard in 1817. Two subspecies are currently recognised: P. bougainville bougainville on Bernier and Dorre Islands, and the extinct mainland form P. bougainville myosura (Maxwell et al. 1996). No studies have been carried out on the genetic structuring of the species, and limited morphological data suggest the current classification is appropriate (Short et al. 1998).
The western barred bandicoot is a member of the Family Peramelidae, and is one of the long-nosed bandicoots of the genus Perameles. It is the smallest bandicoot species, with an average weight of 219 g (Short et al. 1998). They are lightly built animals with large erect ears. Their feet are elongated, with the second and third toes of the hind feet syndactylus (partially fused) and reduced in size, while the fourth toe is long and strongly clawed. Their fur is grizzled, brown-grey in colour, and they are distinguished by darker brown-black bars radiating downwards over the sides of the body from the back. The chin, throat, belly, tops of the feet, and the inner part of the limbs are white (Jones 1923-25; Ovington 1978).
Western barred bandicoots were widely distributed across the southern mainland of Australia at the time of European settlement but have been extinct on mainland Australia since the 1930s (Brooker 1977; Copley et al. 1989; Richards and Short 2003). They occurred in a broad arc from Onslow on the north-west coast of WA, through the WA Wheatbelt, Nullarbor Plain, and arid and semi-arid SA, Victoria and NSW to the Liverpool Plains. The extant subspecies has remained only on Dorre and Bernier Islands in Shark Bay, WA (Figure 3).
Figure 3: Distribution of wild populations of the western barred bandicoot (from van Dyck and Strahan (2008), and including historical and subfossil records)
The remnant wild populations on Dorre and Bernier Islands, estimated to be 757 and 959 respectively as of 2010, are small and subject to substantial fluctuations due to weather (Short and Turner 1993; Short et al. 1997a). In addition, the species was reintroduced to Heirisson Prong at Shark Bay in 1995 and to Faure Island in Shark Bay in October 2005 (Table 2) (Richards and Short 1997; Richards and Short 2003), and 16 individuals from Bernier Island to the Arid Recovery Reserve (ARR) at Roxby Downs in SA (Arid Recovery Project 2002; Arid Recovery 2004). Western barred bandicoots now occur throughout the ARR Main Enclosure and more recently in the Northern Expansion and First Expansion. At Heirisson Prong they are presumed locally extinct since 2008. Details of re-introduction attempts and captive populations are in Appendix 1.
Table 2: Western barred bandicoot populations and groups
Bernier Island (959)
Total of both islands approx. 1716 (2010)
Dorre Island (757)
Translocations in bold are considered successful as they are self-sustaining populations
The western barred bandicoot was an inhabitant of a wide variety of vegetation types in the southern arid and semi-arid zones. Gould (1863) described the range in WA as “inhabits the whole line of coast of the Swan River colony, but, so far as I can learn, is not found to the westward of the Darling Range of hills. It resides in the densest scrub, thickets of the seedling Casuarinae being its favourite resort.” They lived in open saltbush, bluebush and Acacia plains, broken by sandhills and limestone outcrops in western central Australia (Jones 1923-25). On the western slopes of NSW they were recorded from the stony ridges, which branch off from the ranges towards the Darling and Namoi Rivers. In SA they were found on the stony ranges and spurs, which ran down to the “bend of the Murray River”, and in the vast open plains near the head of St Vincent’s Gulf (Gould 1863).
The Shark Bay islands populations are widely distributed through the islands in all habitats, but most likely found in tall scrub (Short et al. 1998). At night they are commonly found in the sandhills and seen occasionally during the day amongst low, dense scrub (Ride and Tyndale-Biscoe 1962). Friend and Burbidge (1995) reported they were common in the scrub associated with stabilised dunes behind the beaches and also occurred on the open steppe associations. At the ARR they survive in very open country, suggesting their habitat requirements may be quite flexible in the absence of introduced predators. They appear to show a preference for nesting in the denser dunes but will forage at night in the more open chenopod swales (K. Moseby7, pers. comm.; Arid Recovery 2004).
Biology and Ecology
Western barred bandicoots are solitary and nocturnal, sheltering during the day in concealed nests. Nests are made in a small hollow dug amongst litter under shrubs. Litter, grasses and other vegetation are used to line an inner chamber. They emerge at late dusk to forage for insects and other small animals, seeds, roots and herbs obtained by digging or hunting (Friend and Burbidge 1995; Visser 2000).
Western barred bandicoots have eight nipples, produce one to three young per litter (usually two), and can have up to four litters per year (Richards and Short 2003). The average litter size on Bernier and Dorre Islands is 1.8 (Short et al. 1998). Gestation is thought to be 12.5 days (as for other bandicoot species), and the period of pouch life is 60 - 70 days. Young are weaned 1 - 2 weeks after vacation of the pouch. Females reach sexual maturity at about 175 g, and males a little later at about 195 g (Short et al. 1998).
Breeding on the islands appears to be strongly seasonal, peaking over winter when the majority of rain falls. The onset of breeding appears to be triggered by the first substantial rain in autumn, following summer drought. Reintroduced animals at Heirisson Prong bred continuously if environmental conditions were good and individuals survived and bred for up to four years (Richards and Short 2003). Western barred bandicoots in the Return to Dryandra enclosure were capable of breeding throughout the year; however, the majority of females bred between May and December, peaking between June and September (33% of females had young or were lactating in summer, 21% in autumn, 67% in winter and 48% in spring (N. Thomas unpublished data). Most females bred twice a year with only a very few producing three litters per year (N. Thomas unpublished data).
Bandicoot numbers on trapping grids on Dorre Island increased substantially in three years from October 1988 to September 1991 after a period of drought prior to April 1989. The population doubled on average each 1.07 years with a rate of increase of 0.65 (Short et al. 1998). During a similar time period from August 1989 to August 1992, bandicoots on Bernier Island increased only slightly, showing little sign of recovery (Short et al. 1998). Bandicoots reintroduced to Heirisson Prong increased at a rate of 0.54 over a three-year period to 1999 in the presence of a low-density feral cat population (Richards and Short 2003) followed by a period of more rapid increase at a rate of 1.08 in a subsequent three-year period to 2006 where cats were only occasionally present (J. Short unpublished data).
Most movements by western barred bandicoots on Bernier and Dorre Islands are less than 400 m; however, males have been recorded moving up to 1020 m over one day, and females up to 490 m over a two-day period (Short et al. 1998). Home range sizes for male and female western barred bandicoots on Dorre Island are 2.5 and 1.4 ha (at high density), and 14.2 and 6.2 ha (at low density), respectively (Friend and Burbidge 1995). The home range of both males and females overlap (Short et al. 1998). The movements of reintroduced western barred bandicoots at Heirisson Prong after release did not pose significant problems for re-establishment (Richards and Short 2003).
At Heirisson Prong the longest surviving free-range bandicoot was at least four years and three months of age, though mean longevity was eight months for males and 10 months for females (Richards and Short 2003). In this case, movement away from the trap lines may have resulted in an underestimate of survival and longevity. At RTDBF western barred bandicoots survived for up to 4.5 years (N. Thomas unpublished data) and at Kanyana Native Fauna Rehabilitation Centre one has survived in captivity to eight years of age (J. Butcher8 pers. comm.).
Although there are no published results for the western barred bandicoot, they are thought to possess a high tolerance to sodium monofluoroacetate (‘1080’ poison) (King 1988). Other species of bandicoot tested (Perameles nasuta, P. gunnii and Isoodon obesulus) survived doses of between 5.4 to 7.7 mg/kg of 1080 (McIlroy 1983). Despite the assumed high tolerance to 1080, western barred bandicoots may be at risk from accidental poisoning during fox, cat, and rabbit control programs due to their small body size, particularly with the use of poisoned ‘One-shot’ oats.