Rainfall deficits gave no clear ozone interaction in US bird richness records in 1995-2024

We tested whether low rainfall made the association of ozone with next-year recorded bird richness more negative. We used a published US Breeding Bird Survey panel and county rainfall baselines. The pooled model used 28,529 accepted surveys on 1,754 routes in 1995-2024. It included route-observer and state-year effects, survey conditions, seasonal weather, and an ozone by temperature term. The interaction was -0.052 recorded species per +10 ppb ozone and +1 standard deviation rainfall deficit, with a 95% interval of -0.166 to +0.061. Four separate East and West, early and late samples gave mixed signs. All four intervals included zero after correction for four tests. Route trends and closer-monitor checks gave the same broad result. This is a test of a relative May-June rainfall deficit, not a direct drought or climate-change test. Coarse exposures, selected routes, few western state clusters, and detection bias limit inference. The result does not establish safety or rule out effects. The package includes the exact input panel, source hashes, code, all estimates, an independent model check, and a figure.

ozone · rainfall deficit · bird richness · observation bias · regional replication · null result