Not everybody accepts the theory of evolution, but those who do have a theory to explain how birds came to be. There are many different parts of birds that are quite specialized because they have developed the ability to fly. They became warm-blooded because warm-blooded animals can change food into energy quickly. They have feathers, not only to keep warm, but because feathers make lightweight flying surfaces. They lost their teeth, because teeth are made of heavy bone. They have developed legs that act as shock absorbers. Their eyesight is very sharp.

When all these specializations came into being is uncertain, but it is known that birds developed from some primitive reptiles millions of years ago. The group of reptiles from which birds are probably descended lived in the Triassic Period about 130,000,000 years ago. This is known from fossils which have been found.

These first birds already had feathered wings, but they probably were not strong fliers. The tails were long with many bones, and the feathers grew from each side. In today’s birds, there is only one tail bone and the feathers grow fanlike from this bone. The old birds had many small sharp teeth.

About 10,000,000 years later some birds still had teeth, but most of the others had already lost them. Fossils of birds from this time show that there were already some birds that had the same size, wing shape, and possibly habits that a bird like the tern has today.

The strange thing is that today we can go over each part of the body of a bird and find traces of the time when birds were reptiles but each part has been adapted to the special needs of the bird.

Perhaps the most important of all these changes was the change from a cold-blooded to a warm-blooded animal. This meant that the eggs of the bird had to be kept at a constant temperature and the young too, had to be kept warm. As a result, birds had to build nests, care for their young, and develop many other functions which are part of the bird’s life today.