NEAR SUN VALLEY, Idaho – Patrick Graham cupped his hands around his mouth and howled into a moonless night. A wolf answered from a distant ridge. Soon, the Pioneer Pack was howling in chorus.

Three miles away, Adrian Alvarado Baldeon, a Peruvian herder, unrolled his sleeping bag on a sagebrush-covered hillside in the Sawtooth National Forest. Fifteen hundred sheep clustered below him, bells tinkling in the darkness.

Bivouacking with sheep high in the mountains around Sun Valley, Idaho, field technicians with the environmental group Defenders of Wildlife are gaining deeper insights into strategies they can use to keep wolves at bay without shooting them. While their effort is four years old, it has gained renewed relevance as residents prepare to vote on a proposed amendment to Idaho’s constitution that will enshrine hunting and trapping as the prime wolf management tool in the state.

The group’s nonlethal experiment, known as the Wood River Wolf Project, is a collaboration with Blaine County officials in central Idaho, the United States Forest Service, the Idaho Department of Fish and Game and some local partners who support alternative ways of protecting wolves in historic sheep-grazing country. The project covers 1,200 square miles, or around half of Blaine County, up from 120 at the program’s inception in 2008.