CHENGDU -- The number of waterbirds arriving at southwest China's Chengdu plain for the winter saw a two-fold growth this year, reaching 20,649, local authorities said on Saturday.

With the support of the local government, the Chengdu Bird Watching Society conducted the investigation. A total of 60 people joined the investigation which covers several rivers and many wetlands in the area.

After nine hours of observation, they recorded a total of 20,649 waterbirds of 58 species. The observers only recorded 9,210 birds during the same period of time last year.

Some endangered species such as Baer's Pochard and Mergus squamatus were discovered in the area.

Shen You, in charge of the bird watching society, said during the dry season, well-managed rivers and wetlands in cities can offer an ideal environment and enough food for birds.

"The activity of migratory birds is an index for ecology," he said, adding the rising number of birds reflects the effects of air, water and soil pollution control.