Sky burial (Tibetan: བྱ་གཏོར་, Wylie: bya gtor, lit. "bird-scattered"[1]) is a funeral practice in which a human corpse is placed on a mountaintop to decompose while exposed to the elements or to be eaten by scavenging animals, especially carrion birds. It is a specific type of the general practice of excarnation. It is practiced in the Chinese provinces and autonomous regions of Tibet, Qinghai, Sichuan and Inner Mongolia, as well as in Mongolia, Bhutan and parts of India such as Sikkim and Zanskar.[2] The locations of preparation and sky burial are understood in the Vajrayana Buddhist traditions as charnel grounds. Comparable practices are part of Zoroastrian burial rites where deceased are exposed to the elements and scavenger birds on stone structures called Dakhma.[3] Few such places remain operational today due to religious marginalisation, urbanisation and the decimation of vulture populations.[4][5]

The majority of Tibetan people and many Mongols adhere to Vajrayana Buddhism, which teaches the transmigration of spirits. There is no need to preserve the body, as it is now an empty vessel. Birds may eat it or nature may cause it to decompose. The function of the sky burial is simply to dispose of the remains in as generous a way as possible (the origin of the practice's Tibetan name). In much of Tibet and Qinghai, the ground is too hard and rocky to dig a grave, and due to the scarcity of fuel and timber, sky burials were typically more practical than the traditional Buddhist practice of cremation. In the past, cremation was limited to high lamas and some other dignitaries,[6] but modern technology and difficulties with sky burial have led to an increased use of cremation by commoners.[7][unreliable source?]

Other nations which performed air burial were the Caucasus nations of Georgians, Abkhazians and Adyghe people, in which they put the corpse in a hollow tree trunk.[8][9]

Source : https://en.m.wikipedia.org/wiki/Sky_burial