BEIJING -- Chinese scientists have discovered the numbers of rare black-necked cranes living in Tibet have risen to about 4,200, state media reported Friday.

According to a new survey conducted by the scientists, an extra 290 birds have taken up residence in Tibet since 1992 suggesting the protected species are happy with their Himalayan habitat, AFP quoted **** China Daily **** as saying.

There are only 6,000 such cranes in the world, with 75 percent of them living in Tibet, **** China Daily **** said, quoting an official with the Tibet Plateau Biological Research Institute.

The birds also can be found in remote areas of Qinghai, Yunnan, Sichuan and Guizhou provinces in western and southwestern China.

Black-necked cranes are the fifth rarest and the least known of all the cranes, according to the U.S.-based International Crane Foundation (ICF), which works worldwide to conserve cranes and the wetland and grasslands on which they depend.

Agricultural encroachment on wetlands is a major threat to this crane, especially in the lower mountain valleys where they winter, ICF said.

Observations of black-necked cranes in Tibet show these cranes feed extensively on waste grain found in harvested barley fields and wheat fields.

Despite protection efforts, many of the historical populations either no longer exist, or exist in much smaller numbers due mainly to the diversion of water for irrigation, the conversion of their habitats to agriculture and tree plantations, and the degradation of habitat caused by heavy livestock grazing.

There is some hunting and egg collecting, but poachers are subject to imprisonment in China, ICF said.

Two reserves for the black-necked cranes have been set up in Tibet, **** China Daily **** said.