Dark-rumped Petrel

Pterodroma phaeopygia sandwichensis

Description

The dark-rumped petrel, Pterodroma phaeopygia sandwichensis, also known as the Hawaiian petrel or 'ua'u, is a seabird that averages 16 in (40 cm) in length with a wingspan of about 36 in (90 cm). It has a short, wedge-shaped tail. The upper body is dark gray; forehead and underparts are white. Wings are white below with conspicuous dark margins. Legs and feet are flesh-colored, and webs are black-tipped. The bill is grayish black, relatively short and stout, with a sharp, downcurving tip. The dark-rumped petrel is one of two subspecies; the other, Pterodroma phaeopygia phaeopygia, is restricted to the Galapagos Islands.

Behavior

Members of the family Procellaridae are sea-birds that can glide long distances close to the surface of the water. They are good swimmers and feed on fish, plankton, and sometimes ship garbage. Petrels nest in colonies on high, barren mountain slopes, entering and leaving the colonies at night. Nesting burrows are used year after year, generally by the same pair and, if damaged, are sometimes re-excavated.

Habitat

On the island of Maui, the dark-rumped petrel currently nests above an elevation of 7,200 ft (2,160 m), where vegetation is sparse. In Haleakala, Maui, dominant plants in nesting areas are grasses and bracken fern. Pukiawe (Styphelia tameiameiae ) dominates in the moist habitat sites. Nesting burrows are commonly located among large rock outcrops, in talus slopes, or along edges of lava flows. Burrows are excavated to depths of 3-6 ft (90-180 cm). Dark-rumped petrels use their nesting habitat between March and November. Present nesting sites may not be preferred habitat but, nevertheless, support the last known viable breeding colonies on the island.

Distribution

The dark-rumped petrel once nested throughout the Hawaiian islands. It spends most of its time at sea, but its pelagic range is not known. Ornithologists recognized by the 1930s that the 'ua'u was in danger of extinction.

The largest concentration of dark-rumped petrel nests are in the upper elevations of Haleakala National Park on the island of Maui. This colony was estimated at about 400 nesting pairs in 1983. Remnant populations have been discovered on a number of the islands, including Hawaii and Lanai, and possibly Molokai and Kauai. A 1988 survey of two populations estimated the population at 431 breeding pairs.

Threats

The mongoose is probably responsible for the decimation of Hawaiian dark-rumped petrel populations. Early descriptions of petrel nesting areas indicated that their burrows were typically found between 1,500 and 5,000 ft (450 to 1,500 m). The present higher elevation colonies are probably the upper limits of most dense predator populations. The restriction of dark-rumped petrels to higher altitudes also suggests the possibility that mosquito-borne diseases may have eliminated populations at lower elevations, as has happened with other Hawaiian birds.

Feral pigs, first introduced by Polynesian settlers and later by European explorers, became well established on all of the larger Hawaiian islands and may prey upon the dark-rumped petrel's eggs.

Conservation and Recovery

In an effort to conserve endangered Hawaiian birds, predator control has been underway since 1966. Both poison and trapping have been used at Haleakala National Park. Recent efforts, however, have been limited to trapping because of severe restrictions on the use of effective poisons. Currently, researchers are working to develop a highly specific poison lethal to the mongoose.

Contact

U.S. Fish and Wildlife Service
Ecological Services
300 Ala Moana Boulevard, Room 3-122
P.O. Box 5088
Honolulu, Hawaii 96850-5000
Telephone: (808) 541-3441
Fax: (808) 541-3470

References

Scott, J. M., et al. 1988. "Conservation of Hawaii's Vanishing Avifauna." Bioscience 38(4):238-253.

Simmons, T. R. 1985. "Biology and Behavior of the Endangered Hawaiian Dark-rumped Petrel." Condor 87:229-245.

U.S. Fish and Wildlife Service. 1983. "Hawaiian Dark-Rumped Petrel and Newell's Manx Shear-water Recovery Plan." U.S. Fish and Wildlife Service, Portland.