Breeding Bird Survey counts of 8 susceptible species were lower in the two years after local human West Nile virus cases in the US, 1990–2024, with no detected weakening after 2012

Question: West Nile virus (WNV) spread across the USA in 1999–2004. Do local WNV outbreaks still decrease Breeding Bird Survey (BBS) counts of susceptible birds, did the effect become smaller, and do high-burden routes keep a long-run deficit? Approach: We used BBS standard surveys on 3,710 conterminous US routes (1990–2024) and CDC county-year counts of human neuroinvasive WNV cases (1999–2025). Local intensity x is log(1 + cases per 100,000) in counties within 50 km of each route. We fitted Poisson models with route x observer and region x year fixed effects for 258 species. The plan, the 8 focal species (LaDeau et al. 2007) and the outcomes were fixed before fitting. Results: An injected effect of -0.300 was recovered as -0.300. Focal-species counts were lower one and two years after local cases (sum of coefficients -0.033 per unit x, 95% CI -0.051 to -0.016; a state bootstrap gave -0.048 to -0.015). This is about 6% fewer birds after a 90th-percentile outbreak year. The clearest species were American Crow (-0.079 +/- 0.024) and Black-capped Chickadee (-0.114 +/- 0.027). The one-year effect was -0.017 in 2000–2012 and -0.013 in 2013–2024 (difference +0.003, CI -0.023 to +0.030). For crows it was larger in 2015–2024 than in 2000–2006. We did not detect a group-level long-run deficit on high-burden routes in 2016–2024 (-0.004, CI -0.039 to +0.032). American Crow had a deficit that grew after 2004, but it was not significant after a Holm adjustment. Limitations: Focal counts were also higher one year before local cases (lead placebo +0.011, CI +0.001 to +0.022). The pre-specified focal-minus-comparison contrast for the one-year lag had a CI that included zero. Single-species state-clustered errors were too narrow (13 of 239 comparison species had |z| >= 3), and random 8-species sets often gave similar means. Human incidence is an indirect measure of bird infection. Thus, the data support lower counts of crows and Black-capped Chickadees after local outbreaks that continue after 2012. The data do not establish that the 8 species as a group differ from other species, or a group-level long-run deficit.

West Nile virus · Breeding Bird Survey · American Crow · Black-capped Chickadee · wildlife disease · dose response · Poisson fixed effects · lead placebo · state bootstrap · CDC ArboNET · population recovery · host adaptation