For centuries birds have fascinated humans. We have marveled at their ability to take to the sky and fly for thousands of years. Our struggle to fly has been chronicled over the centuries in myths and legends. In Greek mythology, Daedalus and his son, Icarus, escaped the labyrinth using wings made of feathers, wax, and thread. In the early eighteenth century, human flight became a reality. The Montgolfier brothers launched the first hot air balloon-and in so doing, captured the imagination of the world as well. In 1903, the Wright Brothers' first successful powered flight finally allowed humans to experience the soaring sensation of a bird.

Birds share certain features with mammals, such as warm-bloodedness and a four-chambered heart. Most living birds can fly; all are descended from ancestors that could fly (Archaeopteryx). The bodies of birds are therefore highly modified for efficiency in flight. The digital and wrist bones of the forelimb are extensively fused to form a rigid support for the large flight feathers of the wing. Fusing of bones for strength and lightness is also found in the skull and pelvic girdle. Many bones of adult birds are hollow rather than filled with marrow and are connected to a system of air sacs dispersed through the body.


Birds come in a variety of sizes and shapes, some beautiful some not. The jaws of modern birds are extended as toothless bills or beaks. Birds have no sweat glands and cannot cool the body by perspiring. When birds are in flight, excess heat is dispersed by the passage of air through the air sacs. When they are at rest, they rid themselves of heat by panting. Birds inhabit every continent and almost every island in the world and are adapted to virtually every ecological environment. Various species live in seemingly sterile deserts, in Antarctica, in jungles, above the tree line on high mountains, in swamps and marshes, on rocky coasts, in woods and fields, and in cities.

All adult birds have feathers, although some species, such as pelicans, kingfishers, woodpeckers, and jays, are completely naked when hatched.The bird body is covered with different types of feathers (collectively called plummage):

Contour feathers cover the body, wings and tail and give the bird its smooth sleek shape
Down feathers are found underneath
the contour feathers and help insulate
a bird.
Flight feathers are shaped to fan the air, creating "lift" to help a bird get off the ground, move about in the air, and land safely.
Bird feet can be adapted for perching, killing prey, or paddling in water.

Feathers are used for flight, warmth, protection (camouflage), and for attracting a mate. Periodically birds must shed their feathers (molt). Feathers are subject to physical wear and become faded and brittle with long exposure to sunlight. At the molt, new feathers grow within follicles in the skin, pushing out the old feathers, which are dead structures. At the base of the tail, is the preen gland. Preening is a process in which the bird uses an oil secreted by the preen gland to lubricate their feathers.

Bird wings act as an airfoil, air passing over the top of the wing travels farther and faster than air passing under the wing. This creates lift, which allows the bird to fly.


The digestive system of the bird is a little different than mammals. Birds have an enlargement of the esophagus, called the crop that stores and moistens food. Birds regurgitate food from the crop to feed baby chicks. A muscular organ called the gizzard kneads and crushes food before it enters the stomach. Sometimes stones that the bird has swallowed remain in the gizzard and are used to grind food. Birds do not store liquid waste in a bladder. Instead kidneys filter waste called uric acid from the blood. Highly concentrated uric acid along with undigested matter from the intestines travels by ducts called ureters to the end of the digestive system called the cloaca. The combination of uric acid and fecal matter is released through the cloaca usually in a white-semi-solid material.

Birds have a poor sense of smell, but have a keen sense of vision. Contrary to the old saying, "eats like a bird," birds are ravenous eaters. Flying requires a tremendous amount of energy, so birds are constantly looking for food. Birds use vocalization, along with other types of bravado to attract a mate. During the breeding season, many male birds demonstrate a behavior known as territoriality. The males will establish an area that they defend in hopes of attracting a mate.A vocal box known as the syrinx allows bird to sing their songs. Fertilization is internal, and the sperm must reach the egg before it hardens. Unlike most warm-blooded animals, birds lay eggs. Since birds are warm-blooded, the embryo must be kept warm during embryonic development. To do this, birds incubate their eggs with a featherless patch of skin on the abdomen called the brood patch. As the embryo develops, a scale-like tooth forms and is used by the chick to crack the eggshell.

Nests hold eggs, conceal chicks from predators, provide shelter from the elements, and sometimes even serve to attract a mate. Birds will periodically leave their nest between breeding and non-breeding seasons. Migration allows birds to avoid climatic extremes and to secure adequate food supplies. Scientists have long that that the length of the day (photoperiod) initiates migration. Innate (unlearned) genetic clocks influence preparation for migration. Birds use two forms of navigarion. Route-based navigation involves following landmarks. Location-based navigation involves using the sun as a compass. Because the sun moves through the sky, birds orient themselves to the sun's position in the sky. Some zoologists suggest that some birds may use the magnetism of the earth as a guide for migration.