Bird
a feathered animal. Scientists put much more into the description of a bird, as air-breathing; having a backbone; warm-blooded; two pairs of limbs, the front pair of wings used for flying or swimming, the hind pair, legs used for walking or swimming; reproducing by hard-shelled eggs, hatched externally; but, after all, the proverb holds true that "a bird is known by its feathers." All birds have feathers. No other animal has feathers. At first thought, flying might be considered a characteristic of birds, but bats fly, and some birds, as the auk, penguin, and ostrich, do not fly.
In the scale of animal creation, birds are lower than mammals and higher than reptiles. A study of fossil birds, of which some five hundred species are known, leads to the conclusion that birds have been developed from reptiles. The earlier birds seem to have been flying reptiles, with teeth, long tails, and scaly feathers.
Living birds may be classified conveniently as follows:
II. Goatsuckers, nighthawks, swifts, and hummingbirds.
III. Parrots and macaws.
IV. Woodpeckers.
V. Cuckoos and kingfishers.
VI. Birds of prey--eagle, owl, vulture, condor, and hawk.
VII. Pigeons and doves.
VIII. Scratching-birds--quail, grouse, turkey.
IX. Shore-birds--plover, woodcock, snipe.
X. Cranes and rails.
XI. Herons and egrets.
XII. Flamingoes.
XIII. Swimmers with comb-edge bills--duck, goose, swan.
XIV. Fully webbed swimmers--pelican, darter, cormorant.
XV. Tube-nosed swimmers--albatross.
XVI. Long-winged swimmers--gull, and tern.
XVII. Diving birds--loon, grebe, auk, murre.
XVIII. Flightless divers--penguin.
XIX. Flightless runners--ostrich, cassowary.
Birds are natural travelers. The great majority of birds change their place of residence with the season. In the spring they travel from the warmer regions toward the poles to nest and return to tropical and sub-tropical climates to winter.
See Ornithology; Nests; Audubon; Archaeopterix; also articles on the different birds mentioned in the table above.