Storm-Petrels: Hydrobatidae

Physical characteristics: The feathers of this 7-inch (18-centimeter), 1.3-ounce (35-gram) bird are completely black except for a white hind-end. The pale coloring reaches across its lower thighs, and there is a band of it across each wing. Even the long legs and bill are black. There is no difference in coloration or size between the males and females.

Geographic range: Wilson's storm-petrels breed on the shores of Antarctica and nearby islands. They are common in the North Atlantic Ocean. Wilson's storm-petrels can be found in all oceans but they avoid the Arctic seas. They come ashore only to breed.

Habitat: Wilson's storm-petrels congregate, gather, along the ocean shelves during the northern summer, and most move back to southern waters to breed.

Diet: Although crustaceans are the preferred food, Wilson's storm-petrels will also eat fish, which has a higher energy content than crustaceans. They find their food by running on top of the water, wings outstretched, and pecking at prey swimming just below the surface. If necessary, the bird will immerse its entire head in the water to catch food.

Behavior and reproduction: Wilson's storm-petrels like to eat in groups, and they are notorious boat followers. These birds are highly migratory, move seasonally, and will travel thousands of miles each year in search of abundant food supplies. Although there is no evidence that petrel pairs remain together throughout migration, they do seem to maintain their bond for several seasons so that the same pair returns to the same nest year after year.

Most nests are built in rock crevices, and the single egg is laid on bare earth in a shallow "bowl" nest in mid-December. The eggs hatch after forty days of incubation, sitting on and warming the eggs for chick development, during which parents take forty-eight hour shifts. Chicks fly on their own for the first time between forty-eight and seventy-eight days old.

Wilson storm-petrels and people: The only interaction with humans occurs when the birds follow fishing boats. Early sailors used to kill Wilson's storm-petrels from the stern of the ship. The birds were attracted to the light, making it easy for them to be caught. Seal hunters would thread wicks through the birds to extract the stomach oil, which would then be used as a candle.

Wilson's storm-petrels find their food by running on top of the water, wings outstretched, and pecking at prey swimming just below the surface. (Illustration by Bruce Worden. Reproduced by permission.)

Conservation status: Wilson's storm-petrel is one of the most abundant birds, due in large part to its isolation from humans. When chicks die, it is usually due to snow covering the entrance to the nest, which makes it impossible for parents to get food to their chicks. ∎