Flying squad of green vigilantes combat bird poachers

Some analysts say authorities are giving green groups such as Liu's a relatively long leash, part of what analysts call "collaborative governance", in some areas of the country.

China's voracious demand for ivory, horns, bones, fins and scales is well documented, alongside the impact that appetite has on animals such as the African black rhinoceros, the Sumatran tiger and the Chinese pangolin.

Less well-known is how millions of birds are caught by poachers in China each year.

The world's fourth-biggest country is a major transit point for birds flying thousands of kilometers on the East Asian-Australasian Flyway from summer breeding grounds in the Northern Hemisphere to wintering areas in the south.

"This is a real bottleneck because on the migration routes ... most of these birds have to pass China," said Johannes Kamp, a biologist from the University of Muenster in Germany who has studied the impact of hunting on birds in China.

Based on figures collated by thousands of activists, poachers trap an estimated 7 million to 10 million wild birds each year.

An exact figure is difficult to ascertain and there is little public information on the prosecution of bird poachers to derive a clearer picture.

"The scale sounds right to me, but I have to say it's very difficult to give a credible estimate," Kamp said. "My gut feeling is that it's in the tens of millions, at least, in China".