Birds are the most diverse terrestrial vertebrates with more than 9,800 extant species. Mammals are the only other homeothermic group with whom they share the planet. Yet, although mammal species number less than half that of birds, the mammals are much more varied in body shape and size. Mammals vary in form from primates to giraffes to armadillos, with specialists in running, hopping, flying, swimming, burrowing, digging, and climbing. Birds, however, all look like birds -with the same basic architecture, a body shape dictated by the demands of flight.
Anatomy of Birds: Feathers of BirdsBirds have three basic types of feathers: down, contour, and flight (wing and tail) feathers. Down feathers are next to the bird's skin for insulation. The contour is the most commonly recognized feather and the one that covers most of the bird's body. Typical contour feathers consist of a central shaft or quill and the flattened portion or vane. Contour feathers that extend beyond the wings and tail are the flight feathers.
Anatomy Birds : Bones of BirdsIn most species both the wings and the legs must be strong enough to transport the full weight of the bird, yet light enough to fly. Some bones have been fused and some bear internal struts. Ribs are overlappei for strength; others are hollowed, thinned, and reduced in numbers lightness. In flying birds, and thos flightless birds like penguins that flipperlike forelimbs to "fly" unde water, the sternum, or breastbone, bears a thin knifelike keel to whic the large flight muscles of the breast; the pectoral muscles, are attached.
Birds' bills are composed of a horny sheath overlying a bony core. The entire lightweight structure has evolved in countless ways to the specialized needs of its owner, from seed-cracking to nectar probing and from fish-catching to fruit-picking. Birds also use their bills to build nests, preen, and court. Bills may change in size and/or color in breeding season.The ROSEATE SPOONBILL uses its spoon-shaped bill to scoop foodfrom water. The EVENING GROSBEAK uses its conical bill to crunch seeds. The BUFF-BELLIED HUMMINGBIRD uses its long needlelike bill to probe into flowers for nectar. The RED CROSSBILL'S bill features mandibles crossed at the tips that are ideal for digging the seeds out of pinecones.
The legs of birds are thin, strong, and springy, and in most species lack feathers on their distal parts where they are instead covered with scales. Muscles, which are concentrated on the portion of the leg nearest the body, control the extremities with a series of tendons. Toes generally number four with three forward and one opposable toe pointed backward, but some North American birds have only three. Toes are covered by scales and have claws at their tips which in birds of prey are enlarged into strong talons.The AMERICAN ROBIN has a typical bird's foot: four toes with three forward and one back. Some, like the HAIRY WOODPECKER, have two toes forward and two back. The MALLARD has three webbed toes and one vestigial toe in back. The DOUBLE-CRESTED CORMORANThas four webbed toes. The BALD EAGLE has daws enlarged and elongated into talons.
The shapes of wings and tails are an adaptation to where and how a bird flies. Look carefully at flight silhouettes: forest raptors (a) have rounded wings for living in dense vegetation; swallows (b) have narrow tapering wings. The tapering wings and narrow tail of a falcon (c) contrast with the broad splayed wings and broad tail of an eagle (d), which allow an eagle to soar. Terns (e) have long elegant wings; albatross wings (f) are very long, with an extended inner section for flying over water like a sailplane.