Ankur Desai

Tonight, like most during the winter migration season, he's hunting the bird poachers of Beijing.

In the skies above us, millions of birds are migrating south for winter.

October in China is the equivalent of rush hour as they head to Australia, New Zealand or even Africa.

As well as navigating through storms and evading predators, they must also avoid the poachers' nets.

OK, where are they?

He's been working with the police, so the police have been nearby in the hope that they would catch the poachers.

Eventually, we hear footsteps.

He's there, he's there, he's there.

Go, go, go, he's there.

Yeah, yeah, he's there.

Careful, careful.

Silva, who's in his 30s, fit and slim, chases the poacher for around two kilometres before calling the police.

He tells them not to move and searches him.

He finds dozens of videos of small birds on the poacher's phone.

They would sell for hundreds of dollars, more than many farmers make in a month.

China is home to more than 1,500 different bird species, about 13% of the global total.

And although there are wildlife laws in place, Silva told us the fines to punish poachers do not outweigh the financial benefits of catching and selling the birds.

He believes many of the poachers and buyers don't even understand why this is a crime.

On a long low wall alongside the Liangshui River in Beijing, a trader in an old military-style uniform sucks on his long wooden pipe.

He has several small cages with tiny birds twittering away inside.