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Australian Pale Field Rat

Rattus tunneyi

French: Rat de Tunney / German: Blasse Australische Feldratte / Spanish: Rata de campo de Australia

Other common names: Pale Field Rat, Tunney’s Rat

Taxonomy. Mus tunneyi Thomas, 1904,

“Mary River,” Northern Territory, Australia.

Rattus tunneyi is sister to a clade containing R. sordidus, R. villosissimus, and R. colletti in the Australian group of Rattus . Two subspecies recognized.

Subspecies and Distribution.

R.t.tunneyiThomas,1904—NAustralia,includingvariousoffshoreIs(Bathurst,Melville,GrooteEylandt,andSirEdward PellewGroup).

R. t. culmorum Thomas & Dollman, 1909 — E Australia.

Descriptive notes. Head—body 118-198 mm, tail 78-190 mm, ear 15-20 mm, hindfoot 25-35 mm; weight 50-210 g. The Australian PaleField Rat is medium-sized, with rounded and broad head. Pelage is long and sleek. Dorsum is grizzled toffee yellowish brown, with grayunderfur, being lightest on sides and cheeks and fades into ventral pelage. Venter is pale gray or creamy white. Feet are covered with short white hair dorsally. Ears are pale pinkish brown;vibrissae are relatively short. Tail is less than 100% of head-body length and unicolored pinkish brown. Skull is broad, with short rostrum. Various helminthes (Syphacia) have been recorded from the Australian PaleField Rat. There are six pairs of mammae. Diploid number is 2n = 42.

Habitat. Tall grassland, cane fields, pastures and some modified habitats, and woodland and monsoon forest with dense grass or sedge understories. The Australian Pale Field Rat burrows in loose sandy soils, which may be a limiting factor determining where it occurs.

Food and Feeding. Australian PaleField Rats are mostly herbivorous, feeding almost exclusively on grass stems, seeds and roots. They favor shoot bases of Alloteropsis and seeds of Sorghum (both Poaceae), Pandanus (Panadanaceae) roots, and some sedges. When food is less plentiful during dry season, it will eat grass seeds lodged in small sandstone outcrops. It is also known to chew through roots of hoop pines ( Araucaria cunninghamii, Araucariaceae) in its burrow systems, making it an agricultural pest. It reportedly eats insects and fungi on occasion, although they make up a fairly small portion ofits diet.

Breeding. Breeding of the Australian Pale Field Rat occurs most commonly in spring in north-eastern New South Wales and January—August in the Northern Territory, although it can breed year-round. Estrouscycles are 4-5 days, and gestation lasts ¢.21-22 days, with postpartum estrus. Litters have 2-11 young, usually four. Young are weaned at ¢.3 weeks old, and sexual maturity can occur as early as five weeks.

Activity patterns. The Australian Pale Field Rat is nocturnal, foraging and moving around at night and resting during the day in burrow systems. It is terrestrial and nests in shallow burrow systems in loose, sandy soils and in termite mounds. Burrows usually have 4-5 entrances, where feces accumulate. A single adult usually occupies a single burrow system, although multiple juveniles can also be found in them. Burrows in termite mounds have entrances at bases, humorously giving them the appearance of small castles. Termite burrows might reduce the risk of flooding in riparian habitats.

Movements, Home range and Social organization. The Australian PaleField Rat has a very scattered distribution with some areas of high density and some of low density. In Kakadu savanna, a high density was 7-4 ind/100 trap-nights. Similarly to other Australian species of Rattus, although not as extreme, populations fluctuate based on climatic variation and water and food availabilities.

Status and Conservation. Classified as Least Concern on The IUCN Red List. Subspecies tunneyi was classified as Vulnerable, and culmorum was classified as Least Concern. The Australian PaleField Rat had a much wider distribution through central and western Australia based on remains from owl pellets, although it is now patchily distributed through western, northern, and eastern Australia. Its pre-European distribution probably included all of Australia. The species seems to be threatened by competition with the Roof Rat ( R. rattus) and might also be affected by cattle grazing that can destroy burrows. It is also threatened by habitat destruction and degradation, with northern Australia being a major unmodified refuge because its distribution has become widely fragmented compared with its pre-European distribution. It is found in various protected areas. Australian Pale Field Rats are considered a native pest because they are known to chew on roots of hoop pines in plantations, which can kill immature plants.

Bibliography. Braithwaite & Griffiths (1996), Burbidge (2016a), Kehl (1980), Menkhorst & Knight (2010), Musser & Carleton (2005), Rowe et al. (2011), Smales (1997), Taylor & Horner (1973), Van Dyck & Strahan (2008), Woinarski, Burbidge & Harrison (2014), Woinarski, Milne & Wanganeen (2001).