Rattus sordidus

721.

Canefield Rat

Rattus sordidus

French: Rat des cannes / German: Australische Zuckerrohrratte / Spanish: Rata de canaveral

Other common names: Dusky Field-rat, Field Rat, Sombre Downs Rat, Sordid Rat

Taxonomy. Mus sordidus Gould, 1858,

“Open plains of Darling Downs,”

Queens-land, Australia.

Rattus sordidus is in the R. sordidus species

group, which clusters with the other Australian species groups. All Australian species aresister to a clade containing the New Guinea endemic species, although not all species have been sampled and more research is needed to fully resolve the relationships within this clade of Rattus. Rattus sordidus previously included R. colletti and R. villossisimus as subspecies, but both are recognized as separate sister species, with R. sordidus being sister to them both. There is apparently an undescribed species from northern Queensland that is a pest in wheatfields, and subspecies of R. sordidus could be recognized with future research. Monotypic.

Distribution. C, S & SE New Guinea and Australia, including NE & E Queensland and South West I (Sir Andrew Pellew Group) off the coast of NE Northern Territory (this population might be extinct).

Descriptive notes. Head-body 110-210 mm, tail 100-160 mm, ear 16-22 mm, hindfoot 27-37 mm; weight 50-260 g (males) and 50-150 g (females). Males are larger than females. The Canefield Rat is medium-sized, with prominently ridged rostrum. Pelage is coarse and spiky. Dorsum is grizzled dark golden brown to black, with buff tips; venter is pale gray and sharply demarcated from dorsum. Feet are pinkish white dorsally, with pale brown soles. Ears are dark brownish gray, short, and rounded; vibrissae are relatively short. Tail is ¢.80% of head-body length and dark gray to black, with obvious rings of scale overlap. Skull has inflated auditory bulla. The helminths Ancistronema coronatum, Nippostrongylus typicus, and Odilia emanuelae have been recorded from Canfield Rats. There are six pairs of mammae: three axillary and three inguinal. Diploid number is 2n = 32, FN = 60.

Habitat. Topical grassland, open forest, grassy patches within clearings in dense forest, and sugarcane fields in Australia and grasslands, specifically in Eucalyptus forests with associated savanna, in New Guinea.

Food and Feeding. Canefield Rats eat stems and seeds of grasses and some broadleafed herbs and insects. They also eat commercial sugarcane. They breaks open the hard outer rine and exposes sap to bacteria, reducing sugar content. Gnawing can leave 20 mm by 50 mm wide gashes or go straight through base ofthe stalk.

Breeding. Canefield Rats reproduce year-round, but females are rarely pregnant in late winter and early spring. Females can become pregnant at 9-10 weeks of age. Gestation is c.3 weeks; litters average six young. Number of females that breed is strongly influenced by rainfall, although it isuncertain if this is because of increased food or the rain itself.

Activity patterns. The Canefield Rat is nocturnal and terrestrial, digging burrows where soil is moist enough.

Movements, Home range and Social organization. Large and discrete colonies of Canefield Rats are usually formed away from canefields, which are invaded after a full canopy of leaves has formed. This behavior is most likely to avoid predation from birds of prey.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The Canefield Rat has a wide distribution and large overall population, is found in many protected areas, and has no major threats. It is considered a major pest to sugarcane.

Bibliography. Aplin, Chesser & ten Have (2003), Baverstock, Gelder & Jahnke (1983), Flannery (1995b), Menkhorst & Knight (2010), Musser & Carleton (2005), Rowe et al. (2011), Smales (1992), Van Dyck& Strahan (2008).