About bird
Birds are a group of warm-blooded vertebrates constituting the class Aves, characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight skeleton. Birds live worldwide and range in size from the 5.5 cm (2.2 in) bee hummingbird to the 2.8 m common ostrich. There are about ten thousand living species, more than half of which are passerine, or "perching" birds. Birds have wings whose development varies according to species; the only known groups without wings are the extinct moa and elephant birds. Wings, which are modified forelimbs, gave birds the ability to fly, although further evolution has led to the loss of flight in some birds, including ratites, penguins, and diverse endemic island species. The digestive and respiratory systems of birds are also uniquely adapted for flight. Some bird species of aquatic environments, particularly seabirds and some waterbirds, have further evolved for swimming.

Bird

low angle photography of flock of silhouette of bird illustration
low angle photography of flock of silhouette of bird illustration
black and yellow bird on branch
black and yellow bird on branch
flying blue and green hummingbird
flying blue and green hummingbird
selective focus photography of red cardinal on tree
selective focus photography of red cardinal on tree
bird on tree branch
bird on tree branch
black and white eagle flying
black and white eagle flying
green and black humming bird
green and black humming bird
shallow focus photography of multi colored bird
shallow focus photography of multi colored bird
close-up photography of multicolored parrot
close-up photography of multicolored parrot
brown and gray bird
brown and gray bird
yellow and black bird on brown wooden post
yellow and black bird on brown wooden post
grey pigeon on flight above the lake
grey pigeon on flight above the lake
yellow bird perched on white flower
yellow bird perched on white flower
white bird
white bird
blue and brown bird on gray tree branch
blue and brown bird on gray tree branch
flock of bird flying in sky
flock of bird flying in sky
white bird flying on mid air
white bird flying on mid air