When four desert bighorn sheep were found dead at Mojave National Preserve in California in 2013, the worst-case scenario was feared. They were killed by a respiratory disease that carried a mortality rate of up to 90 percent, and that carried grave concerns for the preserve's bighorn population. Recent research, however, now suggests that the animals are more resilient to the disease than had been thought.
Bighorn sheep were once common in Southern California and Nevada, but by the 1960s their numbers had been sharply reduced by disease, unregulated hunting, and habitat loss. Forty years of cooperative efforts to rebuild the herds seemed to be paying off until that May day in 2013, when a National Park Service employee found the four dead sheep and spotted other sick animals that appeared to be weak and unsteady with labored breathing.
https://www.nationalparkstraveler.org/2021/02/mojave-desert-bighorn-sheep-showing-resilience-respiratory-disease