What are birds?

Birds are warm-blooded vertebrates with feathers. This easily distinguishes them from all other living animals. Other easily observed features include:

• forelimbs modified as wings
• jaws lacking teeth and with a horny cover
• bipedality (that is, they walk on their two hindlimbs)

There are many other, less obvious, characters that are also important in making birds what they are. Some of these are:

• hollow bones
• skeleton with a marked degree of loss and fusion of bones
• three digits in the hand and four in the foot (with a few exceptions)
• a system of air sacs, which connect with bones
• a special voice box called the syrinx

Although birds cannot be mistaken for any living group of animals, the line between birds and non-birds is much less distinct if fossil animals are examined. Many characters that distinguish birds from other living vertebrates first arose in certain groups of dinosaurs. For this reason, many scientists believe that birds evolved directly from these dinosaurs.

Most, but not all, birds fly. Modifications for flight are throughout the structure of the body, even in flightless forms. Many examples can be seen in the skeleton.

There are about 10,000 species of birds in the world, occurring on all continents. Over 700 have been recorded in Australia and its island territories. Species list

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