Prior ozone and warmth had a clear survey-date interaction only in the early western US sample in 1995-2024

We tested whether prior seasonal ozone changed the link between prior warmth and the next bird survey date. We used a published US Breeding Bird Survey panel. Four region and period models used 30,986 surveys in 1995-2024. Models held route and observer groups and regional year groups fixed. The early western interaction was +1.65 survey days per 10 ppb ozone and 2 C warmth. Its four-test interval was +0.55 to +2.76 days. The other three intervals included zero. Route trends kept the early western result, but a core-June date restriction reduced it to +0.03 days. Thus, a common interaction did not repeat. The result identifies a possible survey scheduling concern. It does not show a climate or pollution effect on birds, or prove that survey timing caused bias in bird counts. Selected routes, coarse exposures, few western state clusters, and missing surveys limit inference. All 32,458 eligible dates matched the raw public file. Code, source hashes, model inputs, figures and independent numerical checks are included.

ozone · seasonal weather · survey timing · observation bias · Breeding Bird Survey · regional replication