CHANGSHA - Fifteen swans have died after being poisoned in Central China's Hunan province, officials said on Monday.

Seventeen swans were found poisoned in the wetlands of Dongting Lake on Sunday afternoon, said Gao Dali, chief of the security section with the East Dongting Lake National Nature Reserve.

Only two swans, which are listed under China's second-level of state animal protection, escaped death.

Thirty-one sarcelles were also killed.

Police said poison was placed near the waters of the nature reserve and they are gathering evidence to arrest the suspects.

A patrol team consisting of experts and volunteers has been set up to prevent similar incidents.

Dongting Lake is located on the lower basin of the Yangtze River and is the second largest freshwater lake in China. The lake area is an important wintering ground for more than 200 species of birds, some of which are under first-level state protection, according to nature reserve statistics.

The poisoning is not the first case at the lake. Last month, a farmer surnamed Sun was detained after found poisoning more than 20 migrant birds including wild geese and ducks in the same region.

A similar incident occurred in Beidagang Wetland Nature Reserve in  North China's Tianjin municipality in November, where 20 oriental white storks were found dead and another 13 poisoned in wetlands tainted by highly-toxic pesticide.

Related stories:

Swans poisoned in C China

Poisoned storks released back into the wild

20 rare birds dead, 13 poisoned in tainted wetlands

Volunteers flocking to help save swans in wetland

Whooper swans paint pretty picture on lake