SGER: Infectious Disease Ecology and Threatened Species: Impacts of West Nile Virus on Spotted Owl Populations

Colorado State University, Fort Collins CO

Investigators

Abstract

West Nile virus (WNV) is a mosquito-borne flavivirus that was first introduced on the east coast of North America in 1999 and can cause serious disease in humans and wildlife, especially birds. By 2003, WNV had spread across North America and first appeared in southern California and by fall 2004 had spread into northern California. The arrival of WNV in northern California could have profound impacts on the extant bird communities, which are naive to the effects of WNV. Although the disease is known to cause mortality in avian species, the potential impacts of WNV on avian populations are largely unknown. However, two recent studies on wild populations of sage grouse and American crows recorded 28% and 72% declines, respectively, in annual survival that were directly attributable to WNV. There is also evidence that owls may be particularly susceptible to WNV from both direct transmission by mosquitoes and indirect transmission from infected prey. Current long-term research on the population dynamics of two subspecies of spotted owls (Strix occidentalis) on 4 study areas in northern California offers a unique opportunity to provide insights on how the introduction of WNV affects avian population dynamics. These long-term studies on spotted owls have collected data on survival, fecundity, recruitment, and rates of population change from marked individuals for the past 10 to 20 years, which provides baseline values of population parameters prior to the introduction of WNV. Using mark-recapture estimators with data from the ongoing spotted owl studies, this research project will differentially examine the ecology of WNV and the effects of this emerging disease on population parameters and rates of population change in spotted owl populations. In this proposal, we are requesting funds to examine the effects of WNV on one of these study populations in 2005, a year with an impending outbreak of WNV. The overall questions to be addressed in this proposal are: 1) what is the prevalence of WNV infection in areas inhabited by northern spotted owls?, 2) what effect does WNV have on spotted owl demographic rates?, and 3) what is the spatial and temporal distribution of direct and indirect sources of infection of WNV in owl territories? We will address these questions by collecting data on mosquito, small mammal, and spotted owl populations. The research will be carried out by a collaborative team of 8 scientists, including 2 wildlife population ecologists conducting spotted owl research, a mosquito ecologist, 3 wildlife disease ecologists with expertise in WNV, a virologist, and a biometrician familiar with modeling wildlife disease dynamics. In addition, 2 undergraduate students will be included in our research program and, thus, provide training for students in the growing field of wildlife disease ecology. In the long-term, we believe this system has promise for predicting the effects of WNV and other introduced pathogens on wild avian populations. We also believe our research can provide insights into the potential impacts of emerging diseases on naive fauna, and further understanding of the dynamics of wildlifedisease systems.