The headquarters at Zakouma National Park, in southeastern Chad, is a sand-colored structure with a crenellated parapet that gives it the look of an old desert fortress. Outside the door to the central control room on the second floor hangs an image of a Kalashnikov rifle, circled in red, with a slash: No weapons allowed inside. Kalashnikovs are ubiquitous in Zakouma. All the rangers carry them. So do the intruders who come to kill wildlife.

Acacias shade the compound, Land Cruisers arrive and depart, and not many steps away, several elephants drink from a pool. Although the animals seem relaxed here, so close to the headquarters hubbub, they aren’t tame; they are wary but thirsty. Zakouma, a national park