Start warmth gave no clear adjusted run-rejection link in four Canada and US bird samples in 1997-2025

We tested whether start temperature was linked to rejection of submitted Breeding Bird Survey runs. We used 48,840 consecutive-year pairs with the same route and observer in Canada and the US. We fit separate models for 1997-2010 and 2011-2025. Models controlled for date, time, duration, assistant status, wind, sky, and state or province by year. Adjusted slopes ranged from -1.45 to +0.38 percentage points of rejection per 5 C. All four intervals that allowed for four tests included zero. A positive slope in later Canadian records was smaller after weather and duration controls. This does not show that screening is free from weather bias. Complete-data filters retained 70,718 of 85,746 standard submitted runs. Runs that were not started or submitted are absent. Extreme warmth was rare in Canada. The study concerns observation selection, not bird survival, pollution, or a causal climate effect.

observation bias · Breeding Bird Survey · weather · temperature · quality screening · null result