Guide to North American Birds

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Photo: Gregory Smith/Flick Creative Commons

Buller's Shearwater

Ardenna bulleri

A cleanly patterned seabird, nesting only near New Zealand but visiting waters off the west coast of North America in fall. Buller's seems more buoyant and graceful in flight than most shearwaters, with more gliding and less flapping. It often arcs up high on one wingtip and then the other, and small flocks may turn and glide over the waves in unison.

Conservation status	On some islands, where colonies had been nearly wiped out by feral pigs, shearwaters re-colonized after pigs were eradicated in 1936. Total population estimated at more than 2 million.
Family	Shearwaters and Petrels
Habitat	Open ocean. Tends to concentrate at areas of strong upwelling, or where warm and cool water currents meet, bringing food to the surface. Rarely comes close to shore. Nests on islands with soil suitable for burrows or with crevices among rocky cliffs.

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Feeding Behavior

Food is taken at or just below surface of water. Forages by dipping to surface in flight, plunging into water from a few feet above surface, swimming with head submerged, sometimes up-ending with head down and tail up. Rarely dives underwater. May feed at night.

Eggs

One. White. Incubation is by both sexes, roughly 51 days. Young: Both parents feed young, by regurgitation. Period from hatching to departure from nest probably about 100 days.

Young

Both parents feed young, by regurgitation. Period from hatching to departure from nest probably about 100 days.

Diet

Crustaceans, fish, squid. Diet not well known. Near breeding grounds may feed mostly on euphausiid shrimp and other crustaceans. Off California, may eat mostly small fish and squid.

Nesting

Breeds on Poor Knights Islands off North Island, New Zealand. Adults arrive there in September, most eggs laid in late November, young depart in May. Breeds in dense colonies. Adults noisy around colonies at night, may climb up into trees to take flight more easily. Nest: Site is in burrow under tree roots or rocks, or in cave or rock crevice. Both sexes help dig burrow. Nest chamber is lined with leaves, twigs, pebbles. Where birds nest in Maori burial caves, may use human bones as nest material.

Illustration © David Allen Sibley.
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Text © Kenn Kaufman, adapted from
Lives of North American Birds

Migration

Breeding adults move north in May, common in parts of North Pacific in summer, returning to New Zealand waters by September. Seen off Pacific Coast of North America mainly June to November, most common September-October; evidently these are mostly nonbreeders and immatures.