U.S. Department of Agriculture: Forest Service -- National Agroforestry Center


Date of this Version



Preventive Veterinary Medicine 114 (2014) 3–10


This article is a U.S. government work, and is not subject to copyright in the United States.


Bighorn sheep currently occupy just 30% of their historic distribution, and persist in popula-tions less than 5% as abundant overall as their early 19th century counterparts. Present-dayrecovery of bighorn sheep populations is in large part limited by periodic outbreaks of respi-ratory disease, which can be transmitted to bighorn sheep via contact with domestic sheepgrazing in their vicinity. In order to assess the viability of bighorn sheep populations onthe Payette National Forest (PNF) under several alternative proposals for domestic sheepgrazing, we developed a series of interlinked models. Using telemetry and habitat data,we characterized herd home ranges and foray movements of bighorn sheep from theirhome ranges. Combining foray model movement estimates with known domestic sheepgrazing areas (allotments), a Risk of Contact Model estimated bighorn sheep contact rateswith domestic sheep allotments. Finally, we used demographic and epidemiologic data toconstruct population and disease transmission models (Disease Model), which we usedto estimate bighorn sheep persistence under each alternative grazing scenario. Depend-ing on the probability of disease transmission following interspecies contact, extirpationprobabilities for the seven bighorn sheep herds examined here ranged from 20% to 100%.The Disease Model allowed us to assess the probabilities that varied domestic sheep man-agement scenarios would support persistent populations of free-ranging bighorn sheep.