Richness at 200 counted birds gave no repeated ozone link in US surveys in 1995-2024

We tested whether previous-season ozone was linked to bird richness after count standardization. We rebuilt species counts from the USGS 2025 Breeding Bird Survey release and joined a published ozone and weather panel. The pooled model used 25,257 accepted surveys on 1,970 routes. We computed expected richness in a random sample of 200 identified birds. Models controlled for route-observer and state-year effects, seasonal weather, current ozone, and survey conditions. Four East and West, early and late estimates ranged from -0.433 to +0.047 species per +10 ppb prior-season ozone. All four intervals included zero after correction for four tests. The pooled slope was -0.252, with a 95 percent interval of -0.473 to -0.030. It weakened with route trends. Thus, a repeated negative link was not established. This does not show that ozone is safe. Rarefaction changes the target measure and does not correct species-specific detection. Selected roadside routes, coarse exposures, missing controls, and few western state clusters limit inference. The package has code, source hashes, exact model inputs, numerical checks, results, and a figure.

ozone · rarefaction · bird richness · weather controls · observation bias · regional replication · null result