A park ranger treads carefully through the trees, stopping to listen for signs of the poacher he’s tailing. Killed for skins, medicine and trophy hunting, the worldwide population of tigers has been reduced to near-extinction at about 3,200. The scale of destruction is increasing, and it will take a three-pronged approach to battle the corruption and financial incentives 

driving the illegal trade: tackling the source, transmission and demand for wild animal products.
Supply could be dealt with by park rangers catching the poachers before they attack, but finding a...