> Grey wolf packs were reintroduced to Yellowstone National Park and Idaho starting in 1995. The subspecies native to the Yellowstone area prior to extirpation was the Northern Rocky Mountains wolf (Canis lupus irremotus) however the species that was reintroduced was the Mackenzie Valley wolf (Canis lupus occidentalis). These wolves were considered as “experimental, non-essential” populations per article 10(j) of the Endangered Species Act (ESA). Such classification gave government officials greater leeway in managing wolves to protect livestock, which was considered one of a series of compromises wolf reintroduction proponents made with concerned local ranchers.
> Indeed, local industry and environmental groups battled for decades over the Yellowstone and Idaho wolf reintroduction effort. The idea of wolf reintroduction was first brought to Congress in 1966 by biologists who were concerned with the critically high elk populations in Yellowstone and the ecological damages to the land from excessively large herds. Officially, 1926 was the year that the last wolves were killed within Yellowstone’s boundaries. When the wolves were eradicated and hunting eliminated, the elk population boomed. Over the succeeding decades, elk populations grew so large that they unbalanced the local ecosystem. The number of elk and other large prey animals increased to the point that they gathered in large herds along valley bottoms and meadows overgrazing new-growth vegetation. Because of overgrazing, deciduous woody plant species such as upland aspen and riparian cottonwood became seriously diminished. So, because the keystone predators, the wolves, had been removed from the Yellowstone-Idaho ecosystem, the ecosystem changed. This change affected other species as well. Coyotes filled in the niche left by wolves, but couldn't control the large ungulate populations. Booming coyote numbers, furthermore, also had a negative effect on other species, particularly the red fox, pronghorn, and domestic sheep. Ranchers, though, remained steadfastly opposed to reintroducing a species of animal that they considered to be analogous to a plague, citing the hardships that would ensue with the potential loss of stock caused by wolves.[3]