The mighty Brahmaputra and its tributaries serve as the winter visiting ground to many migratory birds. From the marshes of Kaziranga to the forests of Eaglenest in western Arunachal and further up to the alpine areas of Arunachal -- one come across more than 750 species of birds that includes most of the winter visitors. Assam, along with the other six northeastern states, shares a common migration route for many of the avifauna that flies over Bhutan, Tibet, China, Myanmar and Bangladesh. The survival of the White-bellied heron (Ardea Insignis), one of the 50 rarest birds in the world that has an estimated global population of less than 250, greatly depends on the existence of their wetland habitat. These birds exist in very low numbers over a large area comprising Bhutan, Yunan in China, northern Myanmar and northeast India. Another rare bird, the black-necked crane breeds on the Tibetan Plateau and winters mainly in the lower altitudes of Quinghai, on the Yunnan-Guizhou Plateau, north-eastern Bhutan and Zemithang and Sangty Valley in West Kameng district of Arunachal Pradesh. It is the only high altitude crane amongst the 15 species found in the world.
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