Birds belong to the Class Aves in the Kingdom Animalia. Birds are the only animals on earth that have feathers and every animal on earth that has feathers is a bird. Other characteristics of birds include: forelimbs modified into wings, lack of teeth, a bill, a four chambered heart, eggs with hard shells, and the furculum (wishbone) among others.
Scientists have divided the Class Aves into 30 orders. Each order is subdivided into families of related genera and species. Scientists group birds together by searching for common structural characteristics of their anatomy and similarities in the genetic material.
There are over 9,000 species of birds worldwide, of that 393 occur in Georgia. Their ability to fly, has enabled birds to inhabit nearly every part of the Earth - from the oceans and frozen polar zones to steaming rain forests and barren deserts. Birds are incredibly diverse in size, color, and lifestyles. They range in size from the 2.5 inch, 0.08 ounce Bee Hummingbird to the Andean Condor with a 10 foot wingspan. Arctic Terns fly 15 to 20,000 miles each year as they migrate from the Arctic to the Antarctic and back! Other birds such as ostriches, rheas, emus, kiwis, and penguins are flightless and depend on running, camouflage, or isolation for protection from predators. Penguins are quite unique, they use their wings for "flying" under water.