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Prev Vet Med. 2014 Apr 1;114(1):3-10. doi: 10.1016/j.prevetmed.2014.01.008. Epub 2014 Jan 15.

A spatial risk assessment of bighorn sheep extirpation by grazing domestic sheep on public lands.

Author information

  • 1EpiCentre, Institute for Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand. Electronic address: t.e.carpenter@massey.ac.nz.
  • 2Oregon Department of Fish and Wildlife, Corvallis, OR, USA.
  • 3United States Forest Service, Intermountain Region, Ogden, UT, USA.
  • 4Payette National Forest, USDA Forest Service, McCall, ID, USA.
  • 5Center for Animal Disease Modeling and Surveillance (CADMS), School of Veterinary Medicine, University of California Davis, Davis, CA, USA.
  • 6Wallowa-Whitman National Forest, USDA Forest Service, Golden, CO, USA.

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.

KEYWORDS:

Bighorn sheep; Epidemic simulation model; Viability analysis; Wildlife disease; Wildlife–livestock interface

PMID:
24507886
DOI:
10.1016/j.prevetmed.2014.01.008
[PubMed - indexed for MEDLINE]
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