Two black-necked cranes (Grus Nigricollis) fly over Lhasa river valley near Lhasa, capital of Tibet Autonomous Region Dec. 11, 2008. Around 7,000 Grus Nigricollis perch in the natural reserve this year. The number of the endangered bird has kept rising by 3.9 percentage annually in the past years due to a series of protection measures. (Xinhua/Gaesang Dawa)

Black-necked cranes (Grus Nigricollis) perch in Lhasa river vally near Lhasa, capital of Tibet Autonomous Region Dec. 11, 2008. (Xinhua/Gaesang Dawa)

A bevy of black-necked cranes (Grus Nigricollis) hover around Lhasa river vally near Lhasa, capital of Tibet Autonomous Region Dec. 11, 2008. (Xinhua/Gaesang Dawa)

A bevy of black-necked cranes (Grus Nigricollis) perch in Lhasa river valley near Lhasa, capital of Tibet Autonomous Region Dec. 11, 2008.(Xinhua/Gaesang Dawa)

A bevy of black-necked cranes (Grus Nigricollis) perch in Lhasa river valley near Lhasa, capital of Tibet Autonomous Region Dec. 11, 2008.(Xinhua/Gaesang Dawa)