Rats, Cats, and Mongooses

The January 2007 issue of Pacific Science (subscription required to either Project Muse or BioOne.2) inaugurates a new series of articles on the Biology and Impacts of Pacific Island Invasive Species with A Worldwide Review of Effects of the Small Indian Mongoose, Herpestes javanicus (Carnivora: Herpestidae) by Warren S. T. Hays and Sheila Conant, who explode a few bits of conventional wisdom.

Abstract: The small Indian mongoose, Herpestes javanicus (E. Geoffroy Saint-Hilaire, 1818), was intentionally introduced to at least 45 islands (including 8 in the Pacific) and one continental mainland between 1872 and 1979. This small carnivore is now found on the mainland or islands of Asia, Africa, Europe, North America, South America, and Oceania. In this review we document the impact of this species on native birds, mammals, and herpetofauna in these areas of introduction.

There is a common story in Hawai‘i that small Indian mongooses failed to control rats in areas of introduction because the mongoose is diurnal and rats are primarily nocturnal (Stone et al. 1994). Most published accounts dispute this story, asserting that the small Indian mongoose served as an excellent cane-field ratter (Pemberton 1925, Barnum 1930, Doty 1945), though it was eventually made obsolete by the development of improved techniques of rat poisoning (Doty 1945).

On Trinidad, Urich (1931) found that rats were rare in cane fields, though they had been a major pest before the introduction of the mongoose in the 1870s. By 1882, a government botanist estimated that the mongoose in Jamaica was saving the colony 100,000 pounds sterling (current value: $8.3 million) per year (Espeut 1882). Spencer (1950, cited by Seaman [1952]), however, found that roof rat populations were as high as 50 per hectare in some parts of St. Croix, despite the presence of mongooses. Seaman (1952) wrote that some cane fields on St. Croix still suffered 25% crop loss due to rats and believed that rats were as much a problem as before the introduction of the mongoose.

Another common story is that mongooses drove rats to become arboreal nesters in areas of introduction (Nellis and Everard 1983). On Hawaiian islands with mongooses, Polynesian rats (Rattus exulans) and Norway rats are terrestrial nesters, whereas roof rats are arboreal nesters. This appears to be true on islands with and without mongooses in Hawai‘i and throughout the world (Baldwin et al. 1952). There is, however, evidence that mongooses alter the relative abundance of rats in favor of arboreal roof rats (Walker 1945). In Puerto Rico, Norway rats are common only in mongoose-free urban areas, whereas roof rats are found in mongoose habitat (Pimentel 1955). Hoagland et al. (1989) made a census of populations of mongooses and rats on St. Croix and Jamaica, and found more roof rats and fewer Norway rats in mongoose habitat.

Nellis (1989) stated that mongooses ‘‘often dominate over’’ cats (Felis catus [domesticus]), though the degree to which they limit the abundance of feral cats in areas of sympatry has not been studied. Feral cats and wild mongooses peacefully share food at artificial feeding sites on O‘ahu, feeding within centimeters of each other (W.S.T.H., pers. obs.). More pertinently, on 3 June 1999, while doing a radio-tracking study, one of us (W.S.T.H.) observed two large male mongooses pass together within 3 m of an adult feral cat, in a relatively undisturbed woodlot and apparently by coincidence, without any of the animals involved showing any sign of excitement or stress even while making eye contact. This anecdotal observation suggests that adults of these species can coexist in peaceful sympatry, at least under some conditions, though it is also possible that they may harry or prey upon each other’s young....

In 1883, sugar planters imported the small Indian mongoose from Jamaica to four Hawaiian islands (Hawai‘i, O‘ahu, Maui, and Kaua‘i) and to the Fijian island of Viti Levu (Gorman 1975, Nellis and Everard 1983). For unknown reasons, the crate of mongooses was kicked off the dock at Kaua‘i, and to date the mongoose has apparently not established there, although a dead mongoose was found in Kaua‘i in 1976 (Tomich 1986). Mongooses were later introduced to the Hawaiian island of Moloka‘i and to the Fijian island of Vanua Levu.