Hawk (bird) - biology.

Hawk (bird) - biology. I INTRODUCTION Hawk (bird), common name for more than 250 species of small to medium-sized predatory birds. Hawks have extremely sharp claws, called talons, which they use to capture, hold, and rip apart their prey. Their name comes from the Middle English word hafoc, which means "to grasp or seize." Hawks are members of a group of raptors, or birds of prey, that hunt for the animals they eat during the day rather than at night. Other birds in this group are ospreys, kites, vultures, and eagles. Hawks are found on many oceanic islands and on all continents except Antarctica. Depending on the species, most hawks live in forests, prairies, marshlands, or open savannas. Some species migrate long distances. The sharp-shinned hawk, for example, breeds in Alaska and Canada during the spring and summer and migrates south to winter in Panama. II CHARACTERISTICS Hawks vary widely in size. The American kestrel is a small hawk that grows about 23 to 30 cm (9 to 12 in) long and has a wingspan of about 50 to 60 cm (about 20 to 24 in). Among the largest hawks is the rough-legged hawk, which is about 56 cm (22 in) long and has a wingspan of 142 cm (56 in). Female hawks are almost always larger than males. Hawks have large, highly developed eyes, which provide the keenest vision of any animal. Their nostrils are located in a leathery patch of skin called the cere, which is just above the bill. Hawks use their strong, hooked bills to tear apart prey that is too large to swallow whole. Hawks with long talons are suited for catching other birds in flight; those with short talons attack flightless animals. Some hawks have both large feet and large talons and can eat a wide variety of prey. III KINDS OF HAWKS There are three types of hawks: accipiters, or woodland hawks; falcons; and buteos, or soaring hawks. These hawks can be identified by the shape of their wings and tails. Accipiters have short, rounded wings and long tails, which they use to dart among trees in pursuit of other birds, their primary food. Falcons have long, sickleshaped wings and long tails, which are suited for chasing other birds at extremely high speeds in the open country. Buteos have broad wings and broad, short tails, which contribute to their soaring flight. Buteos are the hawks most often seen by humans, because they circle high in the air while searching for prey. IV DIET Depending on the species, hawks may eat other birds, such as songbirds and crows, or small mammals, such as squirrels, mice, and rabbits. They also eat frogs, snakes, and insects. Hawks either dive or swoop down on their prey, and the prey may be alive or dead. Some hawks swallow the bones of their prey, along with feathers or fur. Later, they regurgitate, or expel through their mouths, the substances that they are unable to digest. V COURTSHIP AND MATING Many species of hawks have elaborate courtship rituals in which both males and females display their ability to fly steeply up through the air and dive down again. Some hawks circle each other, soaring while holding their wings motionless. They may make steep dives followed by upward climbs. Hawks also make undulating flight displays, with shallow dives and upward swings. In some species, males and females perform cartwheels together in flight. Most hawks have only a single mate in a given year, and some hawks mate for life. Both accipiters and buteos typically build nests of sticks, placed high in trees. Falcons do not build nests: they lay their eggs in shallow scrapes along the sides of cliffs, in holes within trees, or in nests constructed by other birds. Female hawks lay from one to seven brown-spotted, white, or white-blue eggs, depending on the species. The male brings the female food while she incubates or warms the eggs. The chicks hatch after about one month. VI THREATS TO HAWKS Many types of raptors were harmed by the widespread use of DDT and other pesticides that began in the late 1940s. These chemicals dissolve in animals' fatty tissues and are passed from prey to predators. Hawks, like other raptors, accumulated high concentrations of pesticides, which caused females to produce eggs with overly thin shells. Since 1972, when DDT was outlawed in the United States, populations of some species, such as Cooper's hawk, have rebounded. Habitat destruction is now one of the major threats to hawks. Some types of hawks, such as the sharp-shinned hawk of the eastern United States, are declining in parts of their range. Scientific Classification: All hawks are members of the order Falconiformes. Accipiters and buteos belong to the Accipitridae family, and falcons belong to the Falconidae family. The American kestrel is classified as Falco sparverius, the rough-legged hawk as Buteo lagopus, the sharp-shinned hawk as Accipiter striatus, and Cooper's hawk as Accipiter cooperii. Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.