Great Shearwater Life History

Habitat

Breeding Great Shearwaters nest in burrows or rock crevices in areas with tussock grass, ferns, or low woodland. A study of two nesting females breeding on Inaccessible Island found the two birds foraging in different oceanographic conditions—one in cold water (46–50°F) and the other in warmer water (50–61°F). After leaving breeding sites, Great Shearwaters migrate through warm tropical waters, but during the boreal summer, this species is most common in cooler waters over the continental shelf, shelf slope, and banks off the coast of eastern North America. This is a pelagic species, but it does not occur too far offshore, so it can sometimes be seen from land during storms or certain wind conditions.

Food

Great Shearwaters feed mainly on fish, squid, crustaceans, and fish offal. During the nonbreeding season, they frequently gather in large numbers at sea. Great Shearwaters mainly catch food by plunging into the water from as high as 30 feet in the air, often swimming after their prey using their wings as propulsion. They typically dive about 6 feet deep and stay under for around 12 seconds, but dives may go as deep as 60 feet and last 40 seconds. Great Shearwaters occur with other shearwaters, Wilson’s Storm-Petrels, and gulls at fishing trawlers, where they are vocal and scavenge aggressively for discarded fish.

Nesting

Nest Placement

Excavates burrows up to 3 feet long, or nests in rock crevices.

Nesting Facts

Behavior

Millions of Great Shearwaters nest on Gough Island, Nightingale Island, and Inaccessible Island in the South Atlantic. Their return to Gough Island is highly synchronized, with great numbers arriving at breeding areas over a 3–5 day period in September. The birds spend 3–4 weeks courting and mating, and then most of the birds leave in mid-October. During this "pre-laying exodus," adults feed heavily, increasing their weight by more than 10% compared to when they arrived at the islands in September.

Pairs return to the islands in mid-November to lay eggs. Eggs hatch in January and chicks fledge in April or early May. Birds nesting on Gough Island spend about 7 days foraging between nest visits and might travel far enough to reach the coasts of South America and southern Africa.

Great Shearwaters fly strongly, with several stiff rapid wingbeats followed by longer glides on straight wings. In stronger winds, they arc highly and wheel steeply into the wind. It's rare to see shearwaters flapping continuously, the way gulls do, and when they do their wingbeats are stiff and straight-winged.

Conservation

Partners in Flight currently estimates Great Shearwater’s global breeding population at 10 million birds and rates the species a 13 out of 20 on the Continental Concern Score, indicating a species of relatively low conservation concern. As for most seabirds, heavy metals, pesticides, plastic particles, and other marine pollutants pose a risk to their populations. Although this is an abundant species, its reliance on just four known nesting sites makes it susceptible to disturbances at those sites. As for other seabird species, the negative impacts of climate change on habitats and food resources represent an additional, major conservation concern for survival of this species.

Credits

Cuthbert, R.J. (2005). Breeding biology, chick growth and provisioning of Great Shearwaters (Puffinus gravis) at Gough Island, South Atlantic Ocean. Emu. 105(4): 305–310.

Dunne, P. (2006). Pete Dunne's essential field guide companion. Houghton Mifflin Harcourt, New York, USA.

Howell, S. N. G. (2012). Petrels, Albatrosses, and Storm-Petrels of North America: A Photographic Guide. Princeton University Press, Princeton, New Jersey, USA.

Partners in Flight (2021). Avian Conservation Assessment Database, version 2021.

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.

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