Fang and three colleagues at the Wild Duck Lake monitoring station record the species and number of migratory birds. The team is also quick to rescue birds that are injured, treating them onsite during the migration season in spring and autumn.

Established in 2005, the Wild Duck Lake bird monitoring station was originally designed for watching a range of wildlife, but has since become an observation point for migratory birds.

There are 88 wildlife monitoring stations in Beijing. Ten of them are at national level, 33 at municipal level and 45 at district level. They basically cover all key areas of water, the birds' migration routes and their resting places.

Fang said that since February, he and his colleagues have observed more than 650,000 birds.

To minimize human disturbance to the birds, Fang said the wetland park closes from November to March every year. However, the team still needs to patrol the lake several times a day to check birds' health.

"If it is extremely cold, we bring some food for the birds to enable them to survive the tough conditions," he said.