Rattus exulans
Polynesian rat

Polynesian rats (Rattus exulans) have an extensive distribution from Southeast Asia and New Guinea through the Pacific. They spread to several thousands islands in the western and central Pacific Ocean through the colonizing efforts of the Polynesian people. The rats were carried along on the large sea-going canoes with pigs, dogs and jungle cocks. (Dwyer, 1978; Masaharu et al., 2001; Tobin, 1994; Walton et al., 1980)

Rattus exulans can live in a variety of habitats including grassland, scrub and forests, provided that it has adequate food supplies and shelter. It is not a good swimmer, but is able to climb trees for food. Other habitats include the those created by humans, such as houses, granaries, and cultivated lands. These rats usually lives below 1,000 m in elevation, where there is good ground cover and well-drained soil. (Masaharu et al., 2001; Russell, 2002; Tobin, 1994; Williams, 1973)

Rattus exulans has a slender body, pointed snout, large ears and relatively delicate feet. Its back is a ruddy-brown color, with a whitish belly. Mature Polynesian rats are 11.5 to 15.0 cm long from the tip of the nose to the base of the tail. Average weoght is between 40 and 80 g. The tail has fine, prominent, scaly rings, and is about the same length as the head and body combined. Female R. exulans have eight nipples. The skull size has been shown to vary with latitudem with those from cooler climates being larger than those living in warmer climates. A useful feature to distinguish this rat from other species is a dark outer edge on the upper side of the hind foot near the ankle while the rest of the foot is pale. (Russell, 2002; Tobin, 1994)

The lifespan of Polynesian rats is up to one year in the wild. In capitivity this species can live up to 15 months. (Russell, 2002; Tobin, 1994; Williams, 1973)

Polynesian rats are an opportunistic species. In the absence of other rodents they exploit a variety of habitats, ranging from rainforest to grasslands, are able to tolerate different climatic regimes, and are able to persist for long periods at low densities. (Dwyer, 1978)

During the sugar cane harvest, the rats living in the fields either die or migrate to surrounding areas. During the second half of the crop cycle they will rebuild their populations. (Tobin, 1994)

Home Range

Polynesian rats are relitively sedentary and nocturnal. Males travel further than females, but the home range for both sexes decreases as the sugarcane matures. (Tobin, 1994)

Information on communication in Polynesian rats is not available. However, as mammals, it is likely that they use some visual signals in communication. Tactile communication is undoubtedly present, especially between mates and between a mother and her offspring. Scent cues are probably used, also. (Tobin, 1994)

Polynesian rats eat a variety of foods, including broad leaf plants, grasses, seeds, fruits, and animal matter. They prefer fleshy fruits such as guava, passion fruit, thimbleberry, and their favorite sugar cane. Rats that live on the edges of sugar cane fields consume sugar cane as 70% of their diet. To acquire the other additional proteins it will eat earthworms, spiders, cicadas, insects, and eggs of ground nesting worms. (Dwyer, 1978; Russell, 2002; Tobin, 1994; Williams, 1973)

The infestation of Polynesian rats has destroyed the sugar cane fields, especially in Hawaii. To protect the fields in Hawaii, Indian mongooses (Herpestes auropunctatus) were introduced from the West Indies to help control the rats. Barn owls and dogs have also been used to get rid of Polynesian rats. (Russell, 2002; Tobin, 1994; Williams, 1973)

As a prey species, these animals undoubtedly affect predator populations. In their foraging, they affect plant communities, as well as populations of small invertebrates upon which they prey.

Polynesian rats are a major agricultural pest throughout Southeast Asia and the Pacific region. Crops damaged by this species include root crops, cacao, pineapple, coconut, sugarcane, corn, and rice. (Russell, 2002)

Polynesian rats have no positive economic importance to humans. (Tobin, 1994)

Rats are an exotic species in Hawaii and are not protected by law. The rats can be controlled by any method consistent with state and federal law regulations. Mongoose and monitor lizards were introduced to the Pacific islands to attempt to control R. exulans. (Russell, 2002; Tobin, 1994)