Greater Shearwater – Seabird
A Champion of Bird Migration that Breeds in the Southern Hemisphere
The Greater Shearwater, Puffinus gravis, nests in the South Atlantic and follows a surprising migration route that makes it familliar all around the North Atlantic.
Greater Shearwaters, Puffinus gravis, are one of the most common Atlantic seabirds. There are between six and nine million pairs, nesting mainly in a relatively small area of the Southern Pacific, on isolated islands. Most of them breed in the Tristan de Cunha Islands, on the Mid-Atlantic Ridge at about 40º south latitude. (A few nest in the Falkland Islands.) From these remote islands, Greater Shearwaters follow a migration route north at the end of the breeding season, flying up to 12,000 kilometres.
Greater Shearwaters in the Northern Hemisphere
Greater Shearwaters spend most of their time at sea, and are common in northern coastal waters in summer. Leaving the Tristan de Cunha Islands in March and April, they are feeding off North American coasts by May, and continue north to Greenland and across the North Atlantic, with many arriving off European coasts in July and August. A significant number remain off the Canadian Atlantic coast for most of the summer, feeding on fish, squid, and crustaceans.
While bird migration brings many species to the northern hemisphere to breed during the summer season, Greater Shearwaters breed in the Southern Hemisphere and are actually spending their winters in the north. This is why they almost never come to land in the north.
Learning About Greater Shearwaters
A group of scientists and students interested in bird migration, and in the Greater Shearwater in particular, are studying the individuals that spend the summer in the Bay of Fundy near Grand Manan Island on the east coast of Canada. Weighing, measuring, and leg banding the birds, and using satellite transmitters, they are learning about the diet, migration route, and feeding grounds of Greater Shearwaters. They have discovered some interesting things:
- Greater Shearwaters in the Bay of Fundy, foraging at tidal upwellings where currents bring up cold water and abundant food, are feeding mostly on herring and krill. Some eat mostly herring, while others prefer krill.
- The birds eat generously and gain a lot of weight in preparation for their migration south.
- Greater Shearwaters leave the Bay of Fundy by about mid-September, following a roughly Z-shaped migration route across the Atlantic to Africa, south along the African Coast, crossing back to South America, and turning east again to the Tristan de Cunha islands.
- They visit a second foraging ground off the coast of Argentina.
- Greater Shearwaters are capable of flying 32,000 kilometres in about three and a half months.
Greater Shearwaters in the Southern Hemisphere
Arriving back in the breeding grounds after migrating for about 54 days, Greater Shearwaters nest on Nightingale Island, and on Inaccessible and Gough Islands. Pairs return to the same nest each season and raise a single chick. Though pairs reunite during the breeding season, it’s thought that they separate during bird migration and while foraging in the north.
Greater Shearwaters are plentiful and appear to be doing well; however, the fact that they are such wonders of bird migration reveals a possible source of future trouble for them. Ocean fish are in trouble everywhere, overexploited by factory trawlers and illegal fishing fleets. In order for Greater Shearwaters and other seabirds to complete their migration route successfully, there must be plentiful food available along the way. What we do to protect the oceans in the next few years will doubtless determine the fate of many seabirds.
Read about other seabirds:
Hurricanes and Bermuda Petrels
Sources:
Elphick, Jonathan ed. Atlas of Bird Migration. Buffalo: Firefly Books, 2007.
Perrins, Christopher ed. Firefly Encyclopedia of Birds. Buffalo: Firefly Books, 2003
Ronconi, Robert. “The Spectacular Migration of Greater Shearwaters.” Birdwatch Canada. Spring 2007, No. 39: 4-7.
