LHASA, March. 20, 2016 (Xinhua) -- Two water birds chase each other at Lalu wetland in Lhasa, capital of southwest China's Tibet Autonomous Region, March 20, 2016. The biological diversity of Lalu wetland, a national nature reserve, has improved significantly in recent years as more kinds of animals and plants inhabit in China's highest and biggest natural wetland. (Xinhua/Zhang Rufeng)

LHASA, March. 20, 2016 (Xinhua) -- A ruddy shelduck flies over Lalu wetland in Lhasa, capital of southwest China's Tibet Autonomous Region, March 20, 2016. The biological diversity of Lalu wetland, a national nature reserve, has improved significantly in recent years as more kinds of animals and plants inhabit in China's highest and biggest natural wetland. (Xinhua/Zhang Rufeng)

LHASA, March. 20, 2016 (Xinhua) -- A mallard duck flies over water at Lalu wetland in Lhasa, capital of southwest China's Tibet Autonomous Region, March 20, 2016. The biological diversity of Lalu wetland, a national nature reserve, has improved significantly in recent years as more kinds of animals and plants inhabit in China's highest and biggest natural wetland. (Xinhua/Zhang Rufeng) 

LHASA, March. 20, 2016 (Xinhua) -- A pair of ducks chase each other at Lalu wetland in Lhasa, capital of southwest China's Tibet Autonomous Region, March 20, 2016. The biological diversity of Lalu wetland, a national nature reserve, has improved significantly in recent years as more kinds of animals and plants inhabit in China's highest and biggest natural wetland. (Xinhua/Zhang Rufeng) 

LHASA, March. 20, 2016 (Xinhua) -- Water birds fly over Lalu wetland in Lhasa, capital of southwest China's Tibet Autonomous Region, March 20, 2016. The biological diversity of Lalu wetland, a national nature reserve, has improved significantly in recent years as more kinds of animals and plants inhabit in China's highest and biggest natural wetland. (Xinhua/Zhang Rufeng) 

LHASA, March. 20, 2016 (Xinhua) -- Water birds fly over Lalu wetland in Lhasa, capital of southwest China's Tibet Autonomous Region, March 20, 2016. The biological diversity of Lalu wetland, a national nature reserve, has improved significantly in recent years as more kinds of animals and plants inhabit in China's highest and biggest natural wetland. (Xinhua/Zhang Rufeng)