High numbers of migratory birds arriving at Beijing's largest wetland nature reserve indicate there will be an increase in bird numbers over 2012, a conservation expert said Monday.

"According to conservative estimates, we'll have 20,500 migratory birds this spring, an increase of 5,000 from last year," said Li Li, head of the Black Leopard Wildlife Conservation Station, an NGO which helps to protect the birds at the Wild Duck Lake National Wetland Park in Yanqing county.  

"The increasing number of birds is the result of the good conservation work we've done  in the park. We've enclosed the whole 8,600-hectare area, installed 48 security cameras, and conducted 24-hour patrols. In winter we give them food like corn, sorghum and other grain," Li said.

More than 400 whooper swans have already arrived at the wetland, well up on the 36 swans last year. The peak time for migratory birds to arrive is mid-March and visitors can buy tickets to enter the area, said Li.

Bird watchers can expect to see mallards, ruddy shelducks, grey cranes, common goldeneyes and wild geese. They will stay for two months before continuing to migrate northward.

Li said that the migratory routes are fixed and will not be affected by bad weather like smog and sandstorms.

"It's like when you go home at Spring Festival. Birds follow an habitual path, and the wetland is a key place for them to stop. Smog can affect their vision and sandstorms will be a drag when they fly, so such bad weather will prolong their stay in Beijing," Li said.