Boobies and Gannets: Sulidae
Boobies and Gannets: Sulidae
BOOBIES AND GANNETS: SulidaeNORTHERN GANNET (Morus bassanus): SPECIES ACCOUNTS
BLUE-FOOTED BOOBY (Sula nebouxii): SPECIES ACCOUNTS
Boobies and gannets are large seabirds with long, pointed wings, cone-shaped bills, forward-facing eyes, and long necks and tails. Their length is between 25 and 39 inches (64 to 100 centimeters) from their bills to the end of their tails. They are strong fliers and plunge divers—boobies and gannets hit the water headfirst from high in the air in search of fish, and have air sacs under the skin that cushion them when they hit the water.
Boobies and gannets are spread widely over the oceans of the world. Boobies are found mostly in warm tropical or subtropical waters, while gannets usually live in more temperate, cooler regions.
Gannets and boobies live mostly at sea and nest on offshore islands. They usually place their nests on flat ground or on the sides of cliffs. On tropical islands, some also build nests in trees or bushes.
Boobies and gannets feed mostly on schools of fish in ocean waters. Boobies also catch flying fish and squid. They plunge into the water, and they often swallow their prey before swimming back to the surface. By swallowing the fish underwater, they avoid being pestered by gulls and frigatebirds that might try to steal their catch.
BEHAVIOR AND REPRODUCTION
These birds are very sociable and nest close together in large colonies. They have developed a lot of different courtship and pair-bonding displays that the pairs use to say that they belong to each other. The birds hardly ever fight, even though they are so near to each other. Instead, they have displays that tell close-by birds to keep their distance.
Almost all of these birds lay their eggs right on the ground. The two booby species that use trees and bushes build stick nests. Most of these birds lay only one egg. A few lay two or three, but sometimes only one survives. The parents take turns keeping the eggs warm by wrapping their webbed feet around them, and both of them care for the chicks until they are on their own.
BOOBIES, GANNETS, AND PEOPLE
Over the centuries, boobies and gannets and their eggs have been an important source of food for people when the birds were nesting. Some of the birds' droppings were collected and used for fertilizer on farms, often disturbing the birds on their nests. People still eat the birds on some tropical islands, and birdwatchers enjoy them worldwide.
Gannets depend on having smooth wing and tail feathers for their tricky flying, and they need well groomed feathers in order to stay warm in cold water. A gannet fixes its messed-up feathers by running them through its beak. But how can it smooth the feathers on top of its head? One solution is to scratch them with its feet. But during nesting time, gannets have a better solution. Pairs of gannets take turns smoothing the feathers on each other's heads. It is a great way to keep their feathers in shape, and it is also their way of saying, "We belong together."
Abbott's booby is listed as Critically Endangered, facing an extremely high risk of extinction, dying out. It lives only on Christmas Island, where it lost much of its habitat when nesting trees were cleared. The cape gannet is listed as Vulnerable, facing a high risk of extinction, because it has only six breeding colonies. The other gannets and boobies are not in danger of extinction, but many would be better off if their island habitats were protected.
Physical characteristics: The northern gannet is the largest of the three species of gannets. Its feathers are mostly white, with a light rusty color on the back of its head. Northern gannets are between 34 and 39 inches (87 and 100 centimeters) long from their beaks to the end of their tails, and their wingspan is 65 to 70.9 inches (165 to 180 centimeters). Young gannets are mainly dark brown, with feathers gradually lightening until they get their white adult feathers in their fourth year.
Geographic range: Northern gannets breed on offshore islands in the northern Atlantic Ocean. In winter they move south to warmer waters along eastern North America and western Europe and Africa. Some spend the winter in the Mediterranean Sea.
Habitat: Most northern gannets breed on cliffs or flat ground on offshore islands, but some also breed along the rocky shores of continents. When they are not breeding, they spend the rest of the year flying over the ocean, sitting on the water, or diving in to catch fish.
Diet: Northern gannets are seabirds that feed mostly on schools of small fish such as herring. They usually plunge-dive headfirst into the ocean, sometimes from more than 100 feet (30 meters) above the water. Just before entering the water, they fold their wings backward alongside their bodies for a smooth entry. Gannets often hunt in big groups of as many as 1,000 birds. Sometimes northern gannets follow fishing boats and snatch the fish parts that are tossed into the water.
Behavior and reproduction: These birds usually stay with their partners for life, and they meet every year at the same nest site. When they meet, they greet each other with many different courtship displays. For example, they stand face to face with their wings out. Then they knock their bills together and bow to one another.
The birds make flat nests of seaweed and grass glued together with their droppings. The nests are crowded together, but they are spaced just far enough apart so that the birds can't peck each other. Each female lays one egg, and both parents care for the chick. The young bird grows amazingly fast, and by the time it is two months old, it may weigh 50 percent more than its parents. At the age of three months, the chick jumps from its nesting ledge after its parents desert it. The young northern gannet stays at sea the first three years of its life, coming to land only to breed.
Northern gannets and people: Humans used to take chicks for food, but in most places that has stopped. Northern gannets attract a lot of birdwatchers because of their huge nesting colonies and their amazing skill at diving.
Conservation status: Northern gannets are not in danger of extinction. Fishing boats that take large numbers of fish in areas where gannets feed are a threat to the birds. ∎
Physical characteristics: These birds are famous for their bright blue webbed feet. They are large seabirds with long, pointed bills, wings, and tails. Their length is between 29.9 and 33.1 inches (76 and 84 centimeters) from their bills to the end of their tails, and their wingspan is about 60 inches (152 centimeters).
Geographic range: Blue-footed boobies live in cool Pacific waters off the coast of northwest Mexico and southward to the coasts of Peru in South America. They are also found on the Galápagos Islands.
Habitat: Blue-footed boobies breed and roost along rocky coasts on cliffs and small islands. They spend their days at sea in cool waters where there are plenty of fish.
Diet: Blue-footed boobies feed on fish near the shoreline. They usually fly out in groups from the roosts where they spent the night. When they spot a school of fish below, one booby after the next plunges into the water. Other groups of boobies often see them diving from far away, and they join in the feast. Sometimes they catch flying fish near the surface.
Behavior and reproduction: Male blue-footed boobies have some amusing courtship displays. They march around in a high-stepping dance, showing off their blue feet. They nest on the ground, and the female usually lays two eggs. Then the parents keep the eggs warm with their feet. After they hatch, the young boobies are fed by their parents for more than five months.
Blue-footed boobies and people: The name "booby" comes from the Spanish word bobo, which means "stupid or foolish." Sailors long ago noticed that these birds were not afraid of humans, and thought the birds were foolish for letting them grab them and eat them.
Conservation status: Blue-footed boobies are not in danger of extinction. ∎
FOR MORE INFORMATION
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Sibley, David Allen. National Audubon Society: The Sibley Guide to Birds. New York: Alfred A. Knopf, 2000.
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Animal Diversity Web. "Family Sulidae (boobies and gannets)." The University of Michigan Museum of Zoology. http://animaldiversity.ummz.umich.edu/site/accounts/pictures/Sulidae.html (accessed April 15, 2004).
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"Sulidae—Gannets & Boobies." Animals-Online.be http://www.animals-online.be/birds/genten/northern_gannet.html (accessed April 15, 2004).