Petrogale assimilis, Ramsay, 1877

Russell A. Mittermeier & Don E. Wilson, 2015, Macropodidae, Handbook of the Mammals of the World – Volume 5 Monotremes and Marsupials, Barcelona: Lynx Edicions, pp. 630-735 : 716-717

38.

Allied Rock Wallaby

Petrogale assimilis

French: Wallaby de Ramsay / German: Variables Felskanguru / Spanish: Ualabi rupestre de Ramsay

Other common names: Allied Rock-wallaby

Taxonomy. Petrogale assimilis Ramsay, 1877 ,

“Palm Island, on the North-east coast, near Cleveland Bay,” Queensland, Australia.

A member of the lateralis / penicillata group of species (which includes also P. rothschildi , P. lateralis , P. purpureicollis , P. penicillata , P. herberti , P. inornata , P. sharmani , P. mareeba , P. godmani , P. coenensis ). Formerly regarded as a subspecies of P. inornata and earlier of P. penicillata , but reinstated as a species in 1988. The Mareeba and Mount Claro populations were at one time placed within P assimilis , but in 1992 both were described as distinct, separate species (FP. mareeba ; P. sharmani ). Monotypic.

Distribution. NE Queensland from Townsville S to Burdekin and Bowen Rivers, NW to Croydon and SW to Hughenden and Mt Hope; also Palm and Magnetic Is. W limit uncertain.

Descriptive notes. Head-body 44-59 cm (males) and 44.5-55 cm (females), tail 41.9-59.8 cm (males) and 40.9-53.6 cm (females); weight 3.2-5.9 kg (males) and 3.1-5.4 kg (females). Coloration varies with rock substrate. Gray-brown dorsally, but can be dark brown or reddish brown, paler ventrally; arms, legs, and base oftail also pale. Some specimens tend to russet on rump. Pale cheek stripe, slight dark axillary patch, and indistinct dark dorsal head stripe occasionally present. Paws and feet darker than limbs. Tail darkens to almost black toward end, with a slight brush, occasionally with white tip. Moults in autumn to predominantly gray on back and flanks, then progressively browner through year. Diploid chromosome number is 20.

Habitat. Rocky slopes, cliffs, gorges, rocky outcrops, and boulder piles within tropical woodland and open forest.

Food and Feeding. Consumes and prefers predominantly forbs and browse from a variety of plant species growing on rocky outcrops and in surrounding woodland. Plants with stellate trichomes and grasses are also eaten, particularly newly sprouted shoots following rain, but are not preferred. Fruits, seeds, flowers, and insect larvae are also consumed. Does not require access to free water, although females apparently transfer saliva to their young-at-foot.

Breeding. Sexual maturity is reached from 17-5 months in females and 20 months in males. Females are continuous breeders, producing one young per pregnancy (although twins have been recorded). Females exhibit embryonic diapause and postpartum estrus, usually mating within 24 hours of giving birth. Length of estrous cycle has not been determined, but gestation period is 29-34 days. Young spend 6-7-5 months in the pouch and are weaned by 9-13 months, although they continue to associate with their mother for at least a further six months. During drought almost half of young do not survive to weaning. Although birth sex ratios are equal, more male pouch young survive under good environmental conditions and when the mothers are heavier. The mating system appears mixed, with evidence of serial monogamy, occasional extra-pair copulation, and promiscuity. During prolonged droughtjuvenile mortality is very high (almost 90%), and age structure of populations can become heavily skewed in favor of old adults.

Activity patterns. Nocturnal in summer, crepuscular or partially diurnal in other months. Shelters among rocks or within boulder piles during day. In cooler weather will emerge to bask in the sun on nearby exposed rocks, especially in early morning and late afternoon. Individuals typically leave the rocks within half an hour of sunset, forage mostly at night, then return to rocks in the hour before sunrise. Activity is often reduced during rain; in wet season individuals may also return to their shelters during the night to rest.

Movements, Home range and Social organization. Most foraging is conducted in woodland within 200 m of the rocks, but some individuals travel more than 700 m from their rocky shelters to feed. Home-range size (95% adaptive kernel) averaged 16 ha in dry season and 9 ha in wet season, and were similar in both sexes. Individuals show high fidelity to their home ranges over both years and seasons. Home ranges overlapped on average by almost 40% over a season, and overlap was higher between members of the opposite sex than those of same sex, but ranges were generally separated in real time. Long-lasting (up to four years) stable relationships form between mature males and one or sometimes two females. Pair-bonding between adults is characterized by regular mutual allogrooming, by sharing and joint defense of their exclusive daytime shelter and basking sites, and by foraging together (within 5 m) at night. Both males and females are generally intolerant of other individuals, apart from their partner. Aggregations of up to 18 individuals, however, have been reported at an abundant food source. Dispersal appears sex-biased, males dispersing and females philopatric.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The Allied Rock Wallaby is currently common throughout most ofits distribution, although somewhat rarer on the western edge of its range. It may be threatened by habitat degradation as a consequence of cattle grazing and altered fire regimes. It is also vulnerable to predation by domestic/feral cats (Felis catus). It is present in protected areas. Additional research on distribution, general ecology, and the impact of potential threats is required.

Bibliography. Barker (1990), Bell et al. (1989), Bleistein et al. (1994), Blumstein & Daniel (2003a), Close & Bell (1990), Davies (2013), Delaney (1997a, 1997b), Delaney & De’ath (1990), Delaney & Marsh (1995), Delean et al. (2009), Eldridge (1997), Eldridge & Close (1992, 2008a), Eldridge, Johnson et al. (2008), Horsup (1986, 1994, 1996), Horsup & Marsh (1992), Kennedy & Heinsohn (1974), Potter, Cooper et al. (2012), Shar man et al. (1989), Spencer (1991, 1996), Spencer & Marsh (1997), Spencer et al. (1998), Winter, Burnett & Martin (2008d).

Figures

On following pages: 29. Monjon (Petrogale burbidgel); 30. Proserpine Rock Wallaby (Petrogale persephone); 31. Yellow-footed Rock Wallaby (Petrogale xanthopus); 32. Rothschilds Rock Wallaby (Petrogale rothschild); 33. Black- footed Rock Wallaby (Petrogale lateralis).

Distribution. NE Queensland from Townsville S to Burdekin and Bowen Rivers, NW to Croydon and SW to Hughenden and Mt Hope; also Palm and Magnetic Is. W limit uncertain.