Birds are simply a group of warm-blooded vertebrates making up the class Aves. Characterized by feathers, laying hard-shell eggs, four-chambered heart and strong lightweight skeleton, there are approximately 10,000 species worldwide. Strangely, the bird's closest relative is the crocodile and is considered the only living dinosaur. Valued for their colorful beauty and song, some birds are also an important food source, too....Walter Pietrowicz