Hawaii's endemic birds

Abstract

The endemic landbirds of Hawaii, particularly the Hawaiian honeycreepers, an endemic subfamily of the cardueline finches, are one of the world's most dramatic examples of adaptive radiation and speciation (see glossary) in island ecosystems (Freed et al. 1987; Scott et al. 1988). From what is believed to have been a single successful colonization of the Hawaiian Archipelago by an ancestral species from North America, the honeycreepers evolved into a diverse array of species and subspecies of birds with bills ranging from thick, seed-eating beaks of the palila ( Loxioides bailleui ), to small insectivorous bills as seen on the `amakihi ( Hemignathus virens ), woodpecker-like adaptations of the `akiapola`au ( H. munroi ), and large, decurved nectar-feeding bills of the `i`iwi ( Vestiaria coccinea ). In addition to the honeycreepers, the historically documented endemic Hawaiian avifauna included three seabirds, several waterfowl, two raptors, and perching birds that include a species of crow, and representatives of Old World flycatchers, honeyeaters, and thrushes. In all, at least 71 endemic species and subspecies of Hawaiian birds existed at the time of Captain Cook's arrival in the Hawaiian Islands in 1778. Now, however, 76% of the Hawaiian birds are either extinct or endangered, and several of the remaining unlisted species are showing significant population declines. The arrival of humans to the Hawaiian Islands--starting with the Polynesians more than 1,500 years ago and continuing following European contact--drastically changed many natural ecosystems, leading not only to the extinction of many plant and animal species, but also to a significant reduction in both range and abundance for many other taxa. Originally, the Hawaiian birds were found in all habitat zones on each island, but today few native forest birds are found below 610-m (2,000-ft) elevation, and many of the wetland areas that once provided abundant habitat for waterbirds have been destroyed. Of the historically documented 71 taxa of endemic Hawaiian birds, 23 are now extinct, and 30 of the remaining 48 species and subspecies are listed as endangered or threatened by the U.S. Fish and Wildlife Service (USFWS 1992), many with few or only single populations remaining (Fig. 1; Table 1; Table 2). Studies of recently discovered fossil bird bones have further identified nearly 40 additional species of Hawaiian birds never seen alive by the post-Cook naturalists; many of these became extinct after the Polynesians arrived (Olson and James 1982; H. James, Smithsonian Institution, personal communication).