All
birds have feathers. A body covering of feather aids in flight,
insulation, as well as communication.
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Birds
have well-developed nervous systems. Their senses of sight and
hearing are acute, their movement are well-coordinated, and their
behaviors are complex.
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Modifications
in the structure of a bird's claws,wings, and beak reflect their
way of life.
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Modifications
for efficient flight include air sacs, a hollow skeleton , lack of
teeth, absence of a urinary bladder, and a simple reproductive
system. Other adaptations include rapid digestion and excretion to
eliminate excess waste.
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A
four-chambered heart and an efficient circulatory system deliver
large amounts of oxygen to the flight muscles.
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Courtship,
nest building, and care of the young all involve behavior rituals
that vary among species.
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All
birds lay eggs after internal fertilization has occurred. These
eggs are similar to those of reptiles.
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Upon
hatching, practical birds can regulate their body temperature,
obtain their own food, and move about. altricial birds are less
developed at the time of hatching, and require much care from
their parents.
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