The scientific classification of birds is: Kingdom Animalia, Phylum Chordata, Subphylum Vertebrata, Class Reptilia and Subclass Aves. Many scientists consider Aves to be a subclass of Reptilia, rather than its own class. All birds fall in subclass Aves; after that they are further sub-grouped into different orders, families, genera and species.
Birds are related through one common ancestor. There share the characteristics of feathers, hard-shelled eggs and an active metabolism. Most birds also have the ability to fly.
Within the Aves subclass there are approximately 30 different orders of birds. Within that, there are about 180 different families with 2,000 genera and 10,000 species. For example, the American Robin has the scientific classification of Kingdom Animalia, Phylum Chordata, Subphylum Vertebrata, Class Reptilia, Subclass Aves, Order Passeriformes, Family Turdidae, Genus Turdus and Species migratorius.