South Africa's Lions Prosper with Careful Watch and Fenceless Parks

At sunset, a buffalo calf's distressed grunts reverberate through the bush.

But it's a trick.  The grunts are blaring from a loudspeaker, designed to lure lions to a tree and let a South African wildlife reserve carry out a census of its apex predator. As an added enticement, the carcasses of two impalas are affixed to a tree. The scent promises a fresh meal.