BIRDS

 
Birds belong to a class of warm blooded vertebrate animals with feather covered bodies. Next to the mammals, birds are the most important group of land-living vertebrates.All birds have feathers, although in some types, partoculary those that can not fly, the normal structure of the feathers may be much modified and be downy, woolly or straw like. The forelimbs of birds are modified into wings. The bony part of the tail is composed of fathers only. The teeth are absent except in some fossil forms. As in mammals- the only other group of warm blooded animals- the circulation is highly perfected so that there is no mixing of arterial and venous blood, but the arrangement of veins and arteries, by which this is accomplished, is different in the two groups. Birds have keen hearing, although, they have no external ears. The sense of sight also is very keen, but the sense of smell is weak or lacking, except in a few vultures and other birds.