Seasonal ozone and warmth gave no clear common link to next-year observer change on US bird routes in 1995-2023

We tested whether seasonal ozone had a stronger positive link to next-year observer change in warm seasons. We used 27,748 consecutive accepted Breeding Bird Survey pairs on 2,122 US routes. Observers changed in 1,431 pairs (5.16%). Models used route and state-year effects, survey conditions, rainfall, and observer experience. The pooled interaction was -1.13 percentage points per +10 ppb ozone and +5 C seasonal mean maximum temperature, with a 95% interval of -2.28 to +0.01. Four separate East and West, early and late tests gave mixed signs. All four intervals included zero after correction for four tests. Route trends gave a negative pooled estimate, but the separate samples did not establish a common negative pattern. This test concerns observer composition in surveys that returned in the next year. It does not measure all volunteer loss, bird loss, or causal climate effects. Coarse exposures, selected routes, few western state clusters and low event counts limit inference. The package includes code, a model panel, input data, source hashes, validation, and a figure.

observation bias · observer change · ozone · temperature · Breeding Bird Survey · null result