Current and next-year temperature slopes had uncertain differences in matched Canada and US bird surveys in 1985-2024

We tested whether a bird survey richness contrast had a lower temperature slope on the current survey than on the same route survey one year later. We used 49,322 matched survey pairs from Canada and the US in 1985-2004 and 2005-2024. Each pair had the same route and observer. The outcome was recorded taxa in the last ten stops minus those in the first ten. Models controlled both surveys, route-observer effects and state-year effects. Current minus next-year slopes were -0.199, -0.265, -0.235, -0.316 taxa per 5 C. 0 of four primary intervals excluded zero after correction for four tests. The result does not establish a common timing difference. Future weather cannot directly cause an earlier count, but shared causes and selection can limit this test. The study does not identify detection probability, true richness, climate damage or pollution effects. The package gives a frozen published source panel, all estimates, selection counts, figures, source hashes, code and numerical checks.

biodiversity · observation bias · Breeding Bird Survey · temperature · negative control · temporal specificity · matched surveys