Headwaters of the Missouri River, MontanaPepin is a Belgian Malinois, a sleek race-car version of the more common German shepherd. Strong, self-assured, and intensely focused (a littermate was part of Seal Team 6’s takedown of Osama bin Laden), Pepin has trotted across Zambian savannas to find evidence of lions, leopards, and cheetahs, and he’s pushed through lowland tropical rainforests in Myanmar searching out signs of wild elephants. His skill at sniffing out different animals’ dung has given conservationists a quick way to estimate those animals’ populations.

Now on the bank of a clear mountain stream near the Missouri River’s headwaters in Montana, Pepin suddenly dropped onto his haunches and fixed his gaze on ecologist Megan Parker.

This was his signal for having located a target. All morning,