West Nile Virus Ecology in Sagebrush Habitat and Impacts on Greater Sage-Grouse Populations

Emerging infectious diseases can act as important new sources of mortality for wildlife. West Nile virus (Flaviviridae, Flavivirus) has emerged as a potential threat to Greater Sage-Grouse (Centrocercus urophasianus) populations since 2002. We review the ecology of West Nile virus in sagebrush (Artemisia spp.) ecosystems of western North America, summarize the influence of the virus on Greater Sage-Grouse mortality and survival, use demographic models to explore potential impacts on population growth, and recommend strategies for managing and monitoring such impacts. The virus was an important new source of mortality in low- and id-elevation Greater Sage-Grouse populations range-wide from 2003 to 2007. West Nile virus can imultaneously reduce juvenile, yearling, and adult survival—three vital rates important for population growth in this species—and persistent low-level West Nile virus mortality and severe outbreaks may lead to local and regional population declines. West Nile virus mortality in simulations was projected to reduce population growth (i.e., finite rate of increase, ) of susceptible populations by an average of 0.06–0.09/yr. However, marked spatial and annual fluctuations in nest success, chick survival, and other sources of adult mortality are likely to mask population-level impacts in most years. Impacts of severe outbreaks may be detectable from lek-count data, but documenting effects of low to moderate mortality will require intensive monitoring of radio-marked birds. Resistance to West Nile virus–related disease appears to be low and is expected to increase slowly over time. Eliminating mosquito breeding habitat from anthropogenic water sources is crucial for reducing impacts. Better data are needed on geographic and temporal variation in infection rates, mortality, and seroprevalence range-wide. Small, isolated, and peripheral populations, particularly those at lower elevations, and those experiencing large-scale increases in distribution of surface water may be at higher risk.