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NATURAL HISTORY

NEWELL’S SHEARWATER } Puffinus auricularis newelli
FAMILY: Procellariidae

DESCRIPTION: The Newell’s shearwater is a small to medium-sized shearwater measuring 12 to 14 inches with a wing span of 30 to 35 inches. Adults are dark, sooty brown on top contrasted by a striking white underside, with legs and feet that are mainly pale pink. The bird has a black, hooked bill and claws that are well adapted for burrow excavation and climbing. Its flight is fast and usually low over water, powered by rapid wing beats combined with glides.

HABITAT: When not at sea, during the breeding season the species nests primarily in burrows on steep, forested mountain slopes at medium elevation to avoid predation by introduced feral animals.

RANGE: This bird’s distribution at sea is not well known, but many individuals move south and east through the tropical Pacific into the waters of the Equatorial Counter Current. The Newell’s shearwater was once abundant on all main Hawaiian Islands, but it now nests only in the mountainous terrain on the southeasternHawaiian Islands. The species nests principally on the mountains of Kauai, but small colonies exist on Molokai and Hawaii, and possibly on Oahu, Maui, Lanai, and Lehua.

MIGRATION: During the nonbreeding season, Newell’s shearwaters range is in the tropical Pacific Ocean. Wintering range is poorly understood, although Newell’s shearwaters have been recorded moving south and east into the waters of the Equatorial Counter Current.

BREEDING: The bird’s breeding season extends from April to November. It has a clutch size of one egg that is incubated by both parents. The Newell’s shearwater returns to the same nest site year after year.

LIFE CYCLE: The incubation period for the Newell’s shearwater is 53 to 54 days. Chicks fledge at about eight months. The age at first breeding is likely to be around six or seven years. Adult birds may live anywhere from 25 to 40 years.

FEEDING: The species’ diet is not well known, but it includes fish, plankton, and squid. Newell’s shearwaters feed mainly by plunging into the water in order to swallow prey. They can swim underwater, probably down to 10 meters below the surface.

THREATS: A principle threat to this species is depredation of eggs and young by introduced feral predators, including cats, rats, dogs, pigs, and mongoose. In addition, the species is threatened by development, collision with power lines, light pollution, and disturbance of its breeding grounds by invasive plants and feral pigs and goats. Fledgling birds can become grounded when they become disoriented by lights on their nocturnal first flight from the inland breeding sites to the ocean. Once grounded, they are unable to fly and are killed by feral predators, or die from starvation or dehydration. Another leading cause of mortality is collision with power lines at night.

POPULATION TREND: The population estimate for this species is 33,000 to 38,600 birds, with a decreasing trend. It is estimated that the species is declining at rates exceeding 50 percent over the past 47 years (three generations) due to habitat loss, introduced predators, light pollution, and collision with power lines.

 

Newell's shearwater photo © Angela Iwai