South Africa is a country of ranches, farms, reserves and national parks, many surrounded by miles of electric fencing. The fencing keeps out unwanted animal and human intruders, and protects livestock and desirable wildlife.

But the fencing also has a deadly, unintended side effect: It frequently kills smaller animals, particularly birds and reptiles that scientists are eager to conserve. Trip wires are often to blame. Positioned about half a foot off the ground, the wires are meant to send a deterring zap to hungry lions and crop-raiding bush pigs.

But not all creatures respond by turning tail. Tortoises that hit a tripwire withdraw into their shells rather than retreat, while pangolins curl over the wire into a defensive ball. The animals stay put, shocked until their hearts give out.

“Farmers will walk along fences and find six to eight dead tortoises in the space of 100 meters,” said Luke Arnot, a veterinary surgeon and lecturer at the University of Pretoria. “With tortoises, we tend to think of poaching and bush fires, but electric fences are as big, if not a bigger problem.”