BIRDS Birds belong to a class of warm blooded vertebrate animals with feather covered bodies. Next to mammals, birds are the most important groups of land-living vertebrates. All birds have feathers, although in some types, particularly those that cannot fly, the normal structure of the feathers may be much modified and be downy, wooly, or straw like. The forelimbs of birds are modified into wings.The bony part of the tail, except in the very earliest fossil birds, is very short, and the visible tail is composed of feathers only. The teeth are absent except in some fossil forms. As in mammals-the only other group of warm-blooded animal-the circulation is highly perfected so that there is no mixing of material of arterial and venous blood, but the arrangement of veins and arteries by which this is accomplished, is different in 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 few vultures and other birds.
What Causes Weather
Weather is the
physical condition of the atmosphere at a particular time. It includes temperature, air
pressure and water content, known as wind. Winds are formed when the
cooler air moves in to replace the rising warm air. Warm air is usually less dense than
cold air; therefore, it creates low air pressure. Cool air is more dense and creates high air
pressure. Usually we have fine weather when the air pressure is high and there are clouds, rain and snow when the air pressure drops.