671.

Ricefield Rat

Rattus argentiventer

French: Rat des rizieres / German: Reisfeldratte / Spanish: Rata de arrozal

Taxonomy. Epimys rattus argentiventer H. C. Robinson & Kloss, 1916,

Pasir Ganting, west coast of Sumatra, Indonesia.

R. argentiventer is in the R. rattus species group, although additional sampling of lessstudied species is needed to fully resolve its placement and that of other species in the genus. Monotypic.

Distribution. C Laos, Vietnam, C & S Cambodia, SC Thailand, Malay Peninsula, Singapore, Sumatra, Borneo, Java, Bali, and many smaller offshore Is. Introduced into the Philippines (Luzon, Mindoro, Negros, Cebu, and Mindanao Is), Sulawesi, Lesser Sundas (Lombok, Sumbawa, Sangeang, Komodo, Rintja, Flores, Adonara, Lembata, Alor, Sumba, Timor, and Tanimbar Is), New Guinea, and possibly Seram I.

Descriptive notes. Head-body 136-230 mm, tail 149-210 mm, ear 16-24-5 mm, hindfoot 30-41 mm; weight 52-239 g. The Ricefield Rat is medium-sized and similar to the Losea Rat ( R. losea), although it ismuch larger and has an extra pair of mammae. Pelage is sleek and moderately spiny. Dorsum is orangish brown, speckled black throughout, and most individuals have distinctive orangish brown patch in front of each ear that can fade in older individuals. Venter is silvery white to dull gray; dark streak runs lengthwise ventrally. Feet are long and narrow, with broad band of dark hairs dorsally and white on sides and digits. Ears are relatively long and rounded, being lightly furred and similar in color to dorsum;vibrissae are relatively long. Tail is 80-120% of head-body length (usually ¢.100%) and is generally unicolored brown. Skull has larger bulla than in the Roof Rat (R. raftus). There are six pairs of mammae: three axillary and three inguinal pairs. Chromosomal complementis 2n = 42, FN = 61.

Habitat. Various open grassland areas and swampy grasslands. Today, the Ricefield Rat is found primarily in agricultural fields (rice specifically), grasslands, and plantations, being relatively commensal with humans. The species is rarely found in houses. It is usually associated with lowland habitats, but it does occur at higher elevations in some regions.

Food and Feeding. Ricefield Rats eat green vegetation (grasses and paddy weeds), grass seeds including cereal grains, and invertebrates (crabs, mollusks, and insects). Ricefield Rats are significant pests in ricefields and of other crops.

Breeding. Breeding cycle of the Ricefield Ratis closely linked to growth of whatever crop it is found near, mostly rice. Females can have three litters during the rice’s development: first as the rice reaches booting stage, second during ripening, and third right before harvest; peak mating usually occurs just before maximum tilling. Litter size is very large and varies among regions; e.g. 5-7 young/litter in Malaysia and 11-12 inJava. In captivity, embryo counts were 7-8, although up to 18 have been reported. Unusualfor the genus and rodents in general, burrows of Ricefield Rats contain young from previouslitters, not just the newest litter. Young eventually leave burrows after they reach adult size, which might explain how such rapid and high densities can be achieved locally. Pregnancy rates almost up to 100% have been recorded in western Java. Gestation lasts 20-26 days, and intervals between births are usually 20-25 days. Females begin ovulating when they weight 31-40 g or at ¢.28 days of age, although they usually do not become pregnant until they reach 60-120 g. Males usually become scrotal at ¢.59 days of age or weights of ¢.90 g.

Activity patterns. The Ricefield Rat is generally nocturnal, foraging and moving throughout the night. It is mostly terrestrial, although it occasionally climbs. Nests are made in burrows dug by both sexes; pregnant females make the most extensive burrows that they expand as they have more litters.

Movements, Home range and Social organization. Male Ricefield Rats usually live in solitary burrows; no large communal burrows have been reported. Reproduction and increases in density mainly occur when rice is being grown. Densities of 500-600 ind/ ha have been recorded in fields in Indonesia. A significant drop in density occurs after harvesting. When traveling between burrows and feeding areas, regulartrails are used. After harvest, many Ricefield Rats shelter in piles of straw left in the field, and others move to nearby fields.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The Ricefield Rat has a wide distribution, is found in many protected areas, and is considered an agricultural pest throughoutits native and introduced distributions;it is also a vector of various diseases. Rice crops are most affected by Ricefield Rats, and the poison warfarin is commonly used to kill Ricefield Rats to prevent crop loss.

Bibliography. Aplin, Brown et al. (2003), Aplin, Chesser & ten Have (2003), Aplin, Suzuki et al. (2011), Balakirev & Rozhnov (2012), Brown & Singleton (2001), Brown et al. (2005), Buckle et al. (1980), Duncan & Van Peenen (1971), Francis (2008), Lam (1979), Musser (1973a), Musser & Carleton (2005), Namue & Wongsawad (1997), Nguyen Thi My Phung et al. (2011), Phillipps & Phillipps (2016), Ruedas & Aplin (2016), Sinniah (1979), Tristiani & Murakami (1998, 2003), Tristiani, Murakami & Kuno (2000), Tristiani, Priyono & Murakami (1998).