A rising number of migratory birds have been seen arriving for winter at East Dongting Lake in Yueyang, Hunan province, and environmental improvements at the lake are being credited for the increase, officials said.

This winter, about 170,000 migratory birds are expected to arrive at East Dongting Lake, a major part of Dongting Lake, compared with 100,000 to 120,000 seen during winters in the years leading up to 2014, said Zhang Hong, deputy head of administration for East Dongting Lake National Nature Reserve.

There also has been an increase in the types of birds arriving at the 190,000 hectare reserve. Around 2002, some 200 varieties of birds wintered at the lake. The number increased to 345 last winter and had reached 348 as of Dec 10, he said.

"Birds choose places with a pleasant environment for winter. The continued increases suggest improvement of the local environment," said Zhang.

Dongting Lake is the second-largest freshwater lake in China and one of the major water bodies along the Yangtze River, China's longest.

The central government published a national plan for development of the Yangtze River Economic Belt in September 2016 to boost concerted development in riverside regions and provide new growth drivers for the country's economy. Environmental protection and restoration were listed as paramount tasks in the plan.

According to Zhang's administration, local police in Hunan have uncovered 31 cases related to illegal bird hunting and 16 people have received criminal punishment in the past five years. While 28 guns for hunting have been confiscated, more than 1,000 pieces of netting used in bird hunting have been found and removed in the Dongting Lake area.

With financial support of about 100 million yuan ($15.4 million) in recent years from the central government, the reserve has built five protection stations, one publicity and education center and one breeding and veterinary treatment center.

While sand excavation has been banned in the reserve, almost 8 kilometers of shoreline and 69 hectares of bottomland have been restored after local authorities removed 44 sand storage yards, according to the administration.

In addition to government efforts, more residents have also participated in wetland protection. "Last year, residents sent more than 200 injured birds to our reserve," Zhang said.

Zhang Pingyang, a doctoral candidate at the Chinese Academy of Sciences, is in East Dongting for the third year doing research on protection of wetlands and birds.

"Three years is a short period of time when talking about ecological improvement. But I have seen continually enhanced protection efforts and officers have been monitoring the wetland around the clock," she said.