Ecological Factors on Manana Island, Hawaii

Abstract

A 25-ha islet occupied by seasonally nesting sea birds, feral rabbits, and house mice is considered. Rabbits presumably modified the unknown original vegetation in their 70 or more years on the island and reached an equilibrium with a plant cover composed largely of a few hard y introduced grasses. A total of 28 species of higher plants has been recorded from the island, only 6 of which are native to Hawaii. Rabbits occur in low to moderate numbers, sustained by a food source that is enriched by bird guano and subject to annual drought. Average body weight of the mouse is remarkably heavy at 19.5 g. Data on biological and food habits are presented for both mammals. Among 13 species of ectoparasites of birds and mammals are two unusual host adaptations : of the cat flea, Ctenocephalides felis felis, to Oryctolagns cuniculus, and of the Oriental rat flea, Xenopsylla cheopis, to Mus musculus. Rabbits appear not to be detrimental to the nesting of bird s, and their control or extermination is discouraged at present. The scientific importance of the island's unique ecosystem is stressed, and proposals for its intensive study are outlined.