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Human activities are causing major changes in the Earth's biota (1). Extinction, the ultimate change, is occurring today across a broad range of terrestrial and aquatic habitats (2). Although much of this "biodiversity crisis" is due to human impact during recent centuries or decades, few plant and animal communities were unaffected in pre-industrial times (3). Nowhere is this seen more dramatically than on islands in the Pacific Ocean.
Nearly all islands in Melanesia, Micronesia, and Polynesia (Fig. 1) were inhabited by prehistoric peoples. (Figure 1 omitted) Melanesia was occupied as far east as the Solomon Islands by 30,000 years before the present (B.P.) or earlier (4). Much later, about 3500 years B.P., humans arrived in West Polynesia and Micronesia, reaching virtually all of Oceania by 1000 years B.P. (5). Native birds vanished as colonists cleared forests, cultivated crops, and raised domesticated animals (6). Having evolved in the absence of mammalian predators, the birds undoubtedly were tame and easy for people to hunt (7).
The loss of birds on oceanic islands may entail extinction (global loss of a species), extirpation (loss of a species from an island or region, with one or more populations surviving elsewhere), or reduced population. Extinction and extirpation are long-term losses (8), not short-term departures of populations soon to be reestablished from elsewhere (9). All families of Pacific island birds have been affected. Land birds have suffered high levels of both extinction and extirpation, especially among species of rails, pigeons, doves, parrots, and passerines. Although seabird colonies (especially of shearwaters and petrels) have vanished from numerous islands, species of seabirds have undergone little extinction.
Island birds have been lost mainly to predation by humans and nonnative mammals (rats, dogs, and pigs) and because of the removal or alteration of indigenous forests through cutting, burning, and introduction of nonnative plants. The soil erosion caused by deforestation has eliminated nest sites for burrowing seabirds. Although the rate of extinction varied with ruggedness of terrain and size or permanence of the prehistoric human population, we have no evidence that the processes responsible for prehistoric extinctions (10) differed fundamentally from those that continue to deplete surviving species today (11). The differences are mainly technological (snares versus guns and stone adzes and fire versus chain saws and...