world birds atlas by محمد وائل دعبول .. Birds are warm-blooded, bipedal animals whose anatomy is characterized by wings, whose exterior is covered by feathers, and that have, in most cases, hollow bones to assist in flight. Birds are a diverse group, and their bright colors, distinct songs and calls add enjoyment to our lives. They are very visible, quite common, and offer easy opportunities to observe their diverse plumage and behaviors. Because of this, birds are popular to many who pursue wildlife watching and monitoring activities. Being warm-blooded and egglaying, having feathers and wings, birds are the most speciose class of tetrapod vertebrates. With around 10,000 living species, they inhabit ecosystems across the globe, from the Arctic to the Antarctic. They range in size from the 5 cm (Hummingbird) to the 2.75 m ( Ostrich) (1) . The majority of wildlife observations reported by volunteers are birds. In fact, bird watching is the fastest growing recreational pursuit in the United States. America as a nation spend over 2 billion dollars on commercial bird food! Adding all wildlife watching equipment together, including bird food, binoculars, spotting scopes, film, etc., the nation spends nearly 20 billion dollars! (2) Shared characteristics