Introduction

The Bonin Petrel breeds farther north than any other Pterodroma, or gadfly petrel, in the Pacific Ocean. A small, burrow-nesting seabird that breeds colonially, this petrel nests in winter, whereas the only other gadfly petrel nesting in the Hawaiian Islands, the Dark-rumped Petrel (P. phaeopygia), nests in summer. The Hawaiian population of the Bonin Petrel currently breeds in the Northwestern Hawaiian Islands on French Frigate Shoals, Laysan Island, Lisianski Island, Pearl and Hermes Reef, Midway Atoll, and Kure Atoll. Before humans arrived on the Hawaiian Islands, Bonin Petrels inhabited the main islands as well, but this species has since been extirpated there. Surprisingly, no Hawaiian names are known for this seabird. A separate population breeds on the Volcano (Kazan Retto) and Bonin (Ogasawara-gunto) Islands of Japan, but little is known about those birds. Outside of the breeding season, Bonin Petrels in Hawaii disperse west and north toward Japan.

This is one of the few Pterodroma petrels that feed mainly on fish, although squid are also an important food. Bonin Petrels feed mainly at night and are nocturnally active on their breeding grounds; their eyes possess high levels of rhodopsin, a visual pigment thatenhances nocturnal vision.

In the Hawaiian Archipelago, the total breeding population has recently (1980s and 1990s) been estimated to range from 230,396–358,316 breeding pairs (Fefer et al. 1984, Seto 1995). The largest breeding colony in the archipelago, 150,000–250,000 nesting pairs, is now found on Lisianski Island (Fefer et al. 1984, Harrison et al. 1984).

Before rats were introduced to Midway Atoll in 1943, the Midway population was estimated at 500,000 birds, but rat predation has since decimated this population, which is now estimated at about 32,000 breeding pairs (Seto 1995).

The burrow-nesting, pelagic, and nocturnal behaviors of this petrel make it one of the less studied seabirds in the Hawaiian Islands. Key studies, conducted on Midway Atoll and Laysan Island, have focused on food habits, metabolism, temperature regulation, vocalizations, general breeding biology, reproductive success, and chick growth (Howell and Bartholomew 1962; Petit et al. 1981b, 1982a, 1982b; Grant et al. 1981, 1982, 1983; Grant and Whittow 1983; Seto 1994, 1995). Long-term demographic and population studies are needed to document survivorship, differential recruitment, lifetime reproductive success, and accurate estimations of breeding populations.