Prior ozone and warmth gave no clear joint link to large annual bird-count drops in four US samples in 1995-2024

We tested whether prior-season ozone changed the link between prior May-June warmth and a recorded bird-count drop of at least 25%. We used a verified published panel of bird surveys, ozone and county weather. Four East and West, early and late models used 17,636 consecutive-year pairs with the same route and observer. Models controlled route-observer effects, state-year effects and survey conditions. Interaction estimates ranged from -0.98 to +1.16 percentage points per 2 C and 10 ppb. All four corrected intervals included zero. Two early western sensitivity models gave positive signals, but these did not repeat across regions and periods. This result concerns count-drop risk under a linear probability model. It does not show a causal effect or the absence of ecological harm. Seasonal means, monitor error, changing detection, selected routes and few western state clusters limit inference. The package gives the input panel, raw retrieval code, source hashes, all estimates and independent numerical checks.

birds · ozone · temperature · annual count decline · observation bias · regional replication · null result