Cloud cover gave no clear change in end-temperature slopes of bird richness contrasts in Canada and US surveys in 1985-2024

We tested whether cloudy end sky changed the link between end temperature and last-minus-first ten-stop recorded bird richness. We used 58,792 accepted Breeding Bird Survey visits in Canada and the US in 1985-2024. Four country-period models had route-observer and state-year effects, survey weather and timing controls, and sky by temperature terms. Main estimates ranged from -0.035 to +0.154 recorded taxa per +5 C for cloudy versus clear sky. All four intervals included zero after correction for four tests. Route trends, low wind and a 10-30 C end-temperature limit gave the same broad result. These records did not establish cloud protection from morning warmth. Single visits, fixed route order, endpoint weather, selected accepted surveys and approximate cluster intervals limit inference. This is an observation-process test. It does not measure true richness, extreme heat, pollution or causal climate-change effects. The package includes the public input panel, source hashes, code, all estimates, numerical checks, a raw rebuild check and a figure.

bird richness · weather · cloud cover · temperature interaction · observation bias · regional replication · null result