Stranded bighorns

 

It’s not surprising that, in the past, bighorn sheep found the rugged terrain of the Santa Catalina Mountains near Tucson ideal habitat (“The Cost of a Comeback,” HCN, 5/29/17). Whether it is still ideal is the question.

While factors leading to the bighorn’s extirpation in the 1990s have been cataloged, I’m not aware of research that estimates the importance of each. Surely, the encroachment of the Tucson metropolitan area was an important factor. In 2015, Tucson’s population was more than 650,000, while surrounding Pima County had 1.2 million residents. That nearly doubles the 1990 population. 

The bighorn release area in the Pusch Ridge Wilderness is hemmed in right up to the Coronado National Forest and wilderness boundary by dense urban development. The bighorn are stranded on a “mountain island.” How will that herd maintain genetic diversity without manipulation by humans?

The nearest bighorn herd is in the Silverbell Mountains to the west. To reach it, a young bighorn looking for a mate would have to negotiate the newly completed wildlife-crossing structures on Oracle Road/AZ 77 and then would need to cross Interstate 10 with no such accommodation. Mountain lions are not the only, or even the most important, threat to a viable bighorn herd in the Catalinas.

Peggy Wenrick
Tucson, Arizona