Foods of Feral Cats Felis catus on Jarvis and Howland Islands, Central Pacific Ocean

Abstract

Food habits of feral cats (Felis catus) were studied on two small uninhabited islands in the central Pacific Ocean. Cat stomach contents, collected on Howland Island in May 1979 and on Jarvis Island during May 1979 and June-July 1982, revealed that sooty terns (Sterna fuscata) were the primary prey species. Other seabirds, lizards, insects and, on Jarvis Island, house mice were also eaten. Feral cats may have virtually exterminated the wedge-tailed shearwater colony on Jarvis Island. HOUSE CATS, Felis catus (L.), ARE PRESENT IN THE FERAL STATE in a wide variety of habitats including islands from the equator to 540 latitude. It is thought that the house cat was first introduced on various mid-Pacific Ocean islands from the early 19th century to the present by European sailing ships' either intentionally or accidentally releasing cats. Feral populations are now established on most islands with a human population, from the relatively large Hawaiian Islands (Tomich 1969, Kramer 1971) to the minute islands of the Johnston Atoll and in the Tokelau Islands (Kirkpatrick 1966a, b). Unpeopled islands, such as Malden and Starbuck in the Line Islands, often have house cat populations as well (Perry 1980). Established feral cat populations have a profound effect on the native biota, according to various ecological studies. Cats prey on wildlife wherever they are established away from people and their garbage or handouts. Foods taken by them in various parts of the world are reviewed by Fitzgerald and Karl (1979) and by Berkeley (1982). Karl and Best (1982) list foods of feral cats on Stewart Island and review the literature concerning the relationship of feral cats and birds on New Zealand islands. Little has been published, however, on the food habits of feral cats on tropical islands. This paper examines food habits data from feral cats collected on Jarvis and Howland Islands in the central Pacific Ocean. STUDY AREA AND METHODS Jarvis and Howland Islands are managed by the U.S. Fish and Wildlife Service as seabird sanctuaries in the Hawaiian and Pacific Islands National Wildlife Refuge Complex. Jarvis Island (0?23'S, 160?0 1'W) is an uninhabited, low (maximum elevation, 7 m) coral atoll of 414 ha (Fig. 1). Dominant vegetation includes the bunch grass Lepturus repens and succulents Sesuvium sp. and Portulaca sp. (Bryan 1974). A total of 20 bird species have been recorded on the island, seven of which are known to breed there (Clapp 1967). Cats were introduced c. 1935 (King 1973) and were eradicated in 1983 (Rauzon, per. obs.). Howland Island (0?48'N, 176?38'W) is an uninhabited, low (maximum elevation, 6 m) coral atoll of 166 ha in the Phoenix Islands (Fig. 1). Vegetation includes L. repens and other grasses. The succulents Sesuvium sp. and Portulaca sp. are present, as well as small clumps of the woody Cordia subcordata (Bryan 1974). Of the 26 bird species known to occur, six are known to breed on the island (Clapp 1967). The present population of house cats was introduced in 1966 (King 1973). Cats were collected by shooting with .22-caliber rifles and 12-gauge shotguns and by capturing with CONIBEAR? and TOMAHAWK? traps. Stomach contents were analyzed, using procedures discussed in Korschgen (1980), by washing with water, separating washed contents into discrete components, and determining the volume of each component by water displacement and/or visually determining the percentage of each identified component. Identification of ingested items was made or verified by specialists at the U.S. National Museum or at Bernice P. Bishop Museum.