Miyun case

The Miyun Reservoir was one of the capital's top birding sites until several years ago, and also a significant staging site for the white-naped crane. The northern shore of the Miyun Reservoir once had the highest bird diversity in Beijing, and had been a sanctuary for over 110 water bird species, Jia said.

In surveys conducted in 2013 and 2014, Jia and his team counted over 1,000 white-naped cranes at the site. "It could be considered a key stopover site for the cranes during their migration," Jia said.

However, Beijing is also a city with extremely limited water resources, and its underground water has been depleted due to a funnel-shaped geological structure. To address the water shortage, the massive South-to-North Water Diversion Project was carried out, and the Miyun Reservoir was designated as a backup water source for the project.

In 2015, the inflow of water from the Danjiangkou Reservoir in Hubei province caused the water level in the Miyun Reservoir to rise. The farmlands or shore areas that were previously suitable locations for cranes and other waterfowl to roost and feed became either wetlands or totally submerged.

While the rising water level in the reservoir might be good for some water bird species, such as ducks and cormorants, Jia said, it resulted in the decline of habitats for other species, such as cranes.

The decline in water bird diversity at the reservoir may not be irreversible, he said.

"Based on our satellite tracking data, we discovered that over 100 white-naped cranes temporarily stopped at the wetlands on the northern shore of the Miyun Reservoir from March 10 to 12," Jia said.

"It is a very rare record in recent years. It gives us hope. If we can restore the habitat of the Miyun Reservoir to a certain extent, water birds including the white-naped cranes are likely to continue using it as an important stopover site."