Swans are seen at a wetland in Pinglu, north China's Shanxi Province, Dec. 13, 2019. (Xinhua/Zhan Yan)

About 16,000 white swans that migrated to a wetland in north China's Shanxi Province for winter, are now returning to Siberia due to a rise in local temperatures.

Swans are listed as a national second-level protected animal in China and are considered globally vulnerable species.

"Every year between late February and early March, the swans will choose to migrate north when the maximum temperature rises to above 10 degrees Celsius," said Wang Chao, head of the wildlife conservation station of Pinglu County, Shanxi.

In 2012, Pinglu was named "China's Swan County" by the China Wildlife Conservation Association.

The swans were seen practicing taking off, landing and flying after spending more than four months at Pinglu Yellow River Wetland.

"Because of the long journey, the swans' flight will consume a lot of energy. So before returning north, they have to do a lot of flying practice to ensure their successful flight back to Siberia," said He Jianxi, a patroller at Pinglu Yellow River Wetland.

In recent years, with the continuous improvement of the wetland's ecological environment, the number of white swans wintering there annually has topped 10,000.

The wetland, covering over 6,000 hectares, has a pleasant climate and abundant food, and is one of China's three major winter habitats for white swans.