Baku, March 16, AZERTAC They are wintering birds of passage and have been included into the Red Book of Azerbaijan and Red Listed Species of the International Conservation Union (IUCN).They weigh 10-13 kg, and live in flocks. They are mainly of white color and their back, shoulder feathers and top of the tail are of pale gray color. Tip of the wings are black.The bird nests in south-western Europe and Central Asia. They winter in the Black, Caspian, Mediterranean Seas, as well as in the Persian Gulf, in the valleys of Euphrates and Tigris, in India, Pakistan and north-western part of China.When the winter is severe in the northern part of the habitat, their numbers increase in the Azerbaijan Sector of the Caspian Sea, and vice versa, when the winter is mild.