Rattus exulans

669.

Pacific Rat

Rattus exulans

French: Rat de Polynésie / German: Pazifik-Ratte / Spanish: Rata del Pacifico

Other common names: Polynesian Rat

Taxonomy. Mus exulans Peale, 1848,

Tahiti Island (France), Society Islands.

Rattus exulans is in the exulans species group, which is sister to the rattus species group. Rattus exulans was found to be closely related to R. everetti in a recent genetic study, but others have found R. everetti to be related to Limnomys and Tarsomys. There is not considerable geographical variation in R. exulans, but small island populations and northern populations tend to be larger. Rattus exulans probably spread with early seafaring people as they traveled to islands and settled, and it might have been intentionally introduced as a food source in many islands. Subfossils have been found throughout its native and less recent introduced distribution. Monotypic.

Distribution. Probable original distribution includes SE Bangladesh, Myanmar, Laos, Vietnam, Taiwan, Thailand, Cambodia, Malay Peninsula, Sumatra (including offshore Is of Simeulue, Nias, Mentawai Archipelago, and Enggano), Borneo, Java, Bali, and many nearby Is. Introduced into the Philippines, Sulawesi, Moluccas, Lombok, Sumbawa, Flores, Timor, and various other Is in more ancient times (in the last 2000-3000 years) and also to many Melanesian and Pacific Is, including Ryukyu, Hawaii, Christmas, Cocos (= Keeling), Palau, Northern Mariana, Guam, Micronesia, Marshall, Nauru, Kiribati, New Guinea, Bismarck, Solomon, Tuvalu, Tokelau, Futuna, Vanuatu, New Caledonia, Fiji, Samoa, Tonga, Niue, Cook, French Polynesia, Norfolk, New Zealand, and Adele.

Descriptive notes. Head—body 75-165 mm, tail 102-197 mm, ear 15-18 mm, hindfoot 21-30 mm; weight 23-60 g. The Pacific Rat is small, with coarse, harsh, and spiny pelage. Dorsum is reddish brown (more common on island populations) to grayish brown (more common in mainland populations) and generally lighter on sides. Venter is creamy white orgrayish white, with creamy or white-tipped hairs with gray bases; ventral pelage is sharply demarcated from dorsal pelage. Feet are elongated, with brown stripes down outer sides, being white otherwise; inner metatarsal pad is elongated. Ears are long and dark; vibrissae are very long, extending past ears when folded back. Tail is ¢.110% of head—body length, unicolored brown or grayish brown, and sparsely furred. Skull is small. Various species of endoparasites (e.g. Shistosoma, Mastophorus, and Hymenolepisdiminuta) and ectoparasites (e.g. Echinolaelaps and Polyplax) have been recorded from the Pacific Rat. There are four pairs of mammae: one pectoral, one postaxial, and two inguinal. Chromosomal complement is 2n = 42, FN = 62.

Habitat. Close to villages and in disturbed habitat, regrowth vegetation, agricultural fields, and tall grasslands of Imperata and cane grasses (both Poaceae). The Pacific Rat is rarely found in primary habitat, but in places where there are few surviving native rodent species, such as the mountains of Timor, it can commonly be found in primary habitats. It can usually coexistwith or be outcompeted by the Roof Rat (R. rattus) or the Oriental House Rat (R. tanezumi) in villages.

Food and Feeding. The Pacific Rat is generally omnivorous. In New Zealand, seeds, shoots, bark, flowers, root bases, insects at all life stages, and many animal remains were eaten by Pacific Rats. In the Marshall Islands, diets were dominated by various vegetation, although lack of animal foods available on the islands might explain this. In another region, insects were readily available but noteaten unless preferred vegetative food was not available. The Pacific Rat is considered a pest of commercial crops (rice, corn, sugarcane, coconut, cacao, pineapple, and various root crops). Because it also eats many different animals (including eggs and chicks of birds and other mammals), it can be a threat to island species.

Breeding. Reproduction of the Pacific Rate occurs year-round in Malaysia and New Guinea but more often during cooler months in New Guinea. Breeding in Hawaii is restricted to wetter months. For non-lactating females, gestation is ¢.23 days, but for lactating females,it is ¢.3—7 days longer. Litters have 1-7 young in New Guinea and Hawail but up to ten in Malaysia. Young are weaned at 2-3 weeks old. Females generally become sexually active at weights of 32-44 g; males become sexually mature at 41-57 g in Hawaii. In Malaysia, females are often pregnant when they weight more than 30 g.

Activity patterns. The Pacific Rat is generally nocturnal and highly arboreal, often seen climbing around trees, tall grasses, and houses, but it does also travel on the ground. Nests are usually made of leaves of grass, most often in dense grass and ¢.20 cm or more above the ground. Inside buildings, nests are usually found in roof thatch and less often in piles of straw or other material on the ground.

Movements, Home range and Social organization. Densities are 1-3 ind/ha in coconut plantations in Guam, 7-12 ind/ha in grasslands on Ponape, 11-24 ind/ha in coconut plantations in Ponape, and 7-30 ind/ha in Tokelau.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The Pacific Rat has a wide distribution and large overall population, is found in many protected areas, and is considered a major agricultural pest and invasive species, being widely introduced throughout the Pacific islands from Hawaii to Melanesia and New Zealand. It is a major threat to many endemic species of birds, mammals, and reptiles found on the Pacific islands, including New Zealand. Poisoning and trapping are used to control or eradicate Pacific Rats; they have now been extirpated on North Island, New Zealand, through such efforts.

Bibliography. Anderson (1996), Aplin, Brown et al. (2003), Aplin, Chesser & ten Have (2003), Aplin, Suzuki et al. (2011), Balakirev & Rozhnov (2012), Bunn & Craig (1989), Campbell et al. (1984), Claveria et al. (2004), Duncan & Van Peenen (1971), Fall et al. (1971), Flannery (1995b), Ford-Robertson & Bull (1966), Francis (2008), He Yixun et al. (2001), Heaney et al. (2002), Matisoo-Smith (1994), Motokawa et al. (2001), Musser & Carleton (2005), Pages et al. (2013), Phillipps & Phillipps (2016), Robins, Hingston et al. (2007), Robins, MclLenachan et al. (2008), Rowe et al. (2011), Ruedaset al. (2016), Smith &Yan Xie (2008), Tamarin & Malecha (1972), Taylor et al. (1982), Towns et al. (2006).