title: A spatial risk assessment of bighorn sheep extirpation by grazing domestic sheep on public lands.
abstract: Bighorn sheep currently occupy just 30% of their historic distribution, and persist in populations less than 5% as abundant overall as their early 19th century counterparts. Present-day recovery of bighorn sheep populations is in large part limited by periodic outbreaks of respiratory disease, which can be transmitted to bighorn sheep via contact with domestic sheep grazing in their vicinity. In order to assess the viability of bighorn sheep populations on the Payette National Forest (PNF) under several alternative proposals for domestic sheep grazing, we developed a series of interlinked models. Using telemetry and habitat data, we characterized herd home ranges and foray movements of bighorn sheep from their home ranges. Combining foray model movement estimates with known domestic sheep grazing areas (allotments), a Risk of Contact Model estimated bighorn sheep contact rates with domestic sheep allotments. Finally, we used demographic and epidemiologic data to construct population and disease transmission models (Disease Model), which we used to estimate bighorn sheep persistence under each alternative grazing scenario. Depending on the probability of disease transmission following interspecies contact, extirpation probabilities 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 management scenarios would support persistent populations of free-ranging bighorn sheep.
authors: EpiCentre, Institute for Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand. Electronic address: t.e.carpenter@massey.ac.nz.
authors: Tim E
authors: TE
authors: Carpenter
authors: Oregon Department of Fish and Wildlife, Corvallis, OR, USA.
authors: Victor L
authors: VL
authors: Coggins
authors: United States Forest Service, Intermountain Region, Ogden, UT, USA.
authors: Clinton
authors: C
authors: McCarthy
authors: Payette National Forest, USDA Forest Service, McCall, ID, USA.
authors: Chans S
authors: CS
authors: O'Brien
authors: Center for Animal Disease Modeling and Surveillance (CADMS), School of Veterinary Medicine, University of California Davis, Davis, CA, USA.
authors: Joshua M
authors: JM
authors: O'Brien
authors: Wallowa-Whitman National Forest, USDA Forest Service, Golden, CO, USA.
authors: Timothy J
authors: TJ
authors: Schommer
mesh_terms: D063147:Animal Distribution; D000818:Animals; D003247:Conservation of Natural Resources; D017753:Ecosystem; D053476:Extinction, Biological; D007061:Idaho / Q000453:epidemiology; D008954:Models, Biological; D009922:Oregon / Q000453:epidemiology; D011157:Population Dynamics; D018570:Risk Assessment; D012756:Sheep; D012757:Sheep Diseases / Q000453:epidemiology / Q000209:etiology / Q000635:transmission*; D034581:Sheep, Bighorn / Q000502:physiology*; D034561:Sheep, Domestic / Q000502:physiology*; D013686:Telemetry; D014861:Washington / Q000453:epidemiology
keywords: Bighorn sheep; Epidemic simulation model; Viability analysis; Wildlife disease; Wildlife–livestock interface