West Nile virus (WNV) emerged in the western hemisphere during the summer of 1999, reawakening public awareness to the potential severity of vector –borne pathogens.  Since its New World introduction, WNV has caused disease in avian, human and other mammalian communities across the continent.  American crows (Corvus brachyrhynchos) are highly sensitive to the disease, with mortality rates approaching 100%.  We quantified and used dramatic declines in abundance of this susceptible avian host as a proxy for WNV activity to explicitly examine heterogeneity in WNV intensity over a broad spatial range and across multiple land cover types.

Results/Conclusions

Population-wide estimates of American crow abundances declined an average 30% after the emergence of WNV.  However, the spatial pattern of where individual crows were lost varied considerably.  We documented significant declines in crow abundance at 54 of 360 (15%) Breeding Bird Survey (BBS) sites across the eastern United States.  Generally, locations with more area under human development and less forested area were associated with higher odds of WNV impact.  Our findings support an urban-pathogen link, but they also highlight potential non-linearities in this relationship.  While human development significantly affected the probability of a WNV-related population decline in crows, our results suggest that lower intensity (suburban) development may be even more important in facilitating WNV dynamics than higher density urban centers.