West Nile Virus Hammers Backyard Birds
By Shannon LaDeau
Emerging infectious diseases present a formidable challenge to the conservation of species native to North America in the 21st century. However, identifying the impacts of an introduced disease and distinguishing them from other forces that influence population dynamics requires data on species' abundance that extend before and after a pathogen is introduced.
This work draws on avian population dynamics over two decades to evaluate recent impacts of West Nile virus (WNV), a pathogen introduced to North America in 1999, on 20 potential avian hosts across North America using the results from the Breeding Bird Survey, a North American roadside bird survey spanning the last 26 years. This research identifies a wave of declines in bird abundances across the United States that are tightly correlated with the intensity of human West Nile virus epidemics.
The study found regional declines of up to 45 percent in American crow, blue jay, house wren, eastern bluebird, tufted titmouse, and chickadee species (black-capped and Carolina combined). These species are important components of our native, backyard bird community.
Declining Birds
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| American Crow | Blue Jay | House Wren |
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| Eastern Bluebird | Tufted Titmouse | Chickadee |
The ecosystem consequences of this introduced pathogen are the focus of future research, evaluating how subtle and sometimes dramatic changes in population sizes of some species may affect other birds and food webs more broadly.
What Can You Do?
The most simple and effective thing that people can do to curb West Nile Virus, and thereby help backyard birds and people, is to control the number of mosquitoes in their yards by limiting the amount of stagnant water. This could include water collected in trash, planters, dense ground cover, bottle caps, old tires...
This article summarizes the information in this publication:
West Nile virus emergence and large-scale declines of North American bird populations. 2007. Shannon L. LaDeau, A. Marm Kilpatrick, and Peter P. Marra. Nature 447(7145): 710-714.
Emerging infectious diseases present a formidable challenge to the conservation of native species in the twenty-first century. Diseases caused by introduced pathogens have had large impacts on species abundances, including the American chestnut, Hawaiian bird species and many amphibians. Changes in host population sizes can lead to marked shifts in community composition and ecosystem functioning. However, identifying the impacts of an introduced disease and distinguishing it from other forces that influence population dynamics (for example, climate) is challenging and requires abundance data that extend before and after the introduction. Here we use 26 yr of Breeding Bird Survey (BBS) data to determine the impact of West Nile virus (WNV) on 20 potential avian hosts across North America. We demonstrate significant changes in population trajectories for seven species from four families that concur with a priori predictions and the spatio-temporal intensity of pathogen transmission. The American crow population declined by up to 45% since WNV arrival, and only two of the seven species with documented impact recovered to pre-WNV levels by 2005. Our findings demonstrate the potential impacts of an invasive species on a diverse faunal assemblage across broad geographical scales, and underscore the complexity of subsequent community response.
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