In one case in October, Li's team helped to uncover 18,000 birds in 16 plastic foam boxes, including 2,000 yellow-breasted buntings. They had been transported on a cargo flight to Shenzhen airport in Guangdong. Two men were subsequently jailed.

Huang Chunjiang, a government official overseeing the Ruineng market in Qingyuan, one of the biggest in Guangdong, said traders were permitted to sell hundreds of thousands of farm-reared birds and animals annually. But he said it is difficult to verify that all the animals have been raised domestically.

"We must redouble efforts; there's no other way," the State Forestry Administration official said.

"The situation is worsening ... It is a headache for the government because in the market they will sell legal things, but behind the scenes, whether they do other things, no one can say for sure," he added.

The next casualty?

The finch-like yellow-breasted bunting has been extensively hunted in China as a culinary delicacy. Once found in the millions from Japan to Scandinavia, experts say the bird could face extinction like the passenger pigeon of North America, once one of the world's most abundant species.

Last year, the bunting was reclassified as "critically endangered" in the wild, a category short of "extinction", by the International Union for Conservation of Nature, a global authority made up of governments and NGOs.

Other birds affected by poaching in China include chestnut, rustic and little buntings, according to experts. The endangered spoon-billed sandpiper and Nordmann's greenshank are not targeted for food, but they are vulnerable to bird nets.

Activists say the challenge is daunting but they are encouraged by more green volunteers coming forward to beef up the anti-poaching network.

One newcomer, 26-year-old Yue Hua from Ganzhou, Jiangxi province, gave up a pharmaceutical career to become a full-time activist.

"After witnessing the environment of my hometown worsen due to mining, I wanted to do something," he said.

"I hope man and nature can coexist harmoniously. That's my dream."