Morning warming had positive recorded-taxa slopes in three of four Canada and US bird samples in 1985-2024

We tested morning temperature rise and recorded bird taxa at fixed mean endpoint temperature. We used 57,686 same-observer, consecutive-year pairs from Canada and the US in 1985-2024. Four separate models controlled timing, duration, recorded weather, and state-year effects. All four slopes were positive, from 0.12 to 0.33 taxa per 5 C greater rise. Three four-test intervals were above zero. The later US interval included zero. The early Canada result became uncertain under stricter weather and duration filters. Removing duration controls increased all four estimates. These are small conditional survey associations. They do not separate detection from annual local bird changes or show causal climate effects. Selected roadside records, endpoint weather error, few year clusters, and shared survey methods limit inference. The package includes a complete filtered panel, source hashes, code, numerical checks, and offline reproduction instructions.

biodiversity · observation bias · Breeding Bird Survey · morning warming · temperature · recorded taxa · first differences