The Dark-rumped Petrel is an endangered seabird that ranges across much of the tropical Pacific, but nests only in the Hawaiian and Galapagos Islands. The name Pterodroma is derived from the Greek words pteron, which refers to feathers or wings, and dromos, which refers to a racecourse or any quick movement. “ Phaeopygia ” is derived from the Greek phaios, for dusky or brown, and puge, for rump or buttocks ( Gotch 1981 ). Thus, the name describes a fast-flying, dark-rumped bird.
This petrel is a member of a large order of seabirds, the Procellariiformes, long-winged pelagic birds that are characterized by their tube-shaped nostrils. Most come to land only to breed and are highly adapted to an ocean existence ( Alexander 1954 , Tuck and Heinzel 1978 ). Members of the family Procellariidae, which also contains the shearwaters and the fulmars, Dark-rumped Petrels are often called gadfly petrels because of their erratic, swooping flight behavior at sea. The 25 species of gadfly petrels in the genus Pterodroma are most commonly found in tropical and subtropical zones, where they feed primarily on squid, fish, and crustaceans caught near the sea surface at night.
This account focuses on the Hawaiian subspecies of the Dark-rumped Petrel (Pterodroma phaeopygia sandwichensis), or ‘Ua‘u, which once nested on all of the main Hawaiian Islands. Historically a common breeding seabird in the Hawaiian Islands, its populations were decimated, initially by Polynesians who prized the birds as a delicacy, and more recently by predators that were introduced during the past centuries. Current breeding-population estimates from known nest sites on the islands of Maui and Hawai‘i range from 450 to 650 pairs. Total population estimates, based on observations of birds at sea and birds flying inland on Kaua‘i Island, range from several thousand to 34,000 birds. The Galapagos Islands subspecies (P. p. phaeopygia) nests on 5 islands within that archipelago, with an estimated breeding population of 35,000 pairs ( Coulter 1984 ).
Like other Procellariiformes, Dark-rumped Petrels depend on sparse and widely dispersed food resources, which dictate a conservative reproductive strategy marked by late maturity, low replacement rates, and long life spans. Individuals are unable to respond quickly to favorable conditions by increasing their fecundity, and even under optimum conditions populations are capable of only low rates of increase. Thus populations are vulnerable to increases in adult mortality rates, which, in the case of this species, have been caused by human disturbance and the introduction of nonnative predators to breeding colonies, leading to substantial declines in Dark-rumped Petrel populations in recent history. Active management of the remaining populations will be required to prevent the extinction of this species.