The Vertebrate call Aves includes the birds. It is estimated that there are 9000 species worldwide. Birds have remarkable characteristics that make them unique and allow them to fly. They have a "one way" breathing system that allows them to breath easier while flying, they have light yet durable hollow bones, a skeleton where many bones are fused or lost, powerful flight muscles, and feathers. Another characteristic is that birds are endothermic.
White-throated sparrow ( Zonotrichia albicollis )
Introduction to aves. (2010). Retrieved from http://www.ucmp.berkeley.edu/diapsids/birds/birdintro.html
