Prior ozone and warmth gave no clear joint link to low recorded bird richness in four US samples in 1995-2024

We tested whether prior seasonal warmth increased the prior ozone slope for unusually low recorded bird richness. We used a published US Breeding Bird Survey panel. Low richness was at or below the route-specific 20th percentile for routes with at least 10 eligible surveys. Four separate East and West, early and late samples used 28,404 surveys. Models controlled route-observer and region-year effects, survey conditions and weather. Interaction estimates ranged from 0.11 to 1.48 percentage points per 5 ppb ozone and 1 C. All four primary adjusted intervals included zero. Under this model, all upper bounds were below a 5-point reference size. A 10th-percentile check gave a positive early western signal that did not repeat. This result does not establish safety or a causal effect. Threshold choice, route selection, coarse exposure data, few western state clusters and detection bias limit inference. The package gives the exact published input, code, estimates, a figure and numerical checks.

birds · ozone · seasonal warmth · low richness · observation bias · regional replication · null result