Spring warmth gave no clear repeated curvature in Orange-tip flight dates in England and Wales in 1985-2024

We tested whether the link between spring warmth and mean Orange-tip flight date became weaker in warmer springs. Four weighted site-effect models used 19,259 site-years in England and Wales in 1985-2004 and 2005-2024. Models controlled winter warmth, the March-April temperature contrast, spring rain, time and peak count. Quadratic temperature coefficients were +0.127, -0.369, -0.065 and +0.543 days per degree C squared. All four adjusted delete-year jackknife intervals included zero. All planned count, boundary, site-duration and common-site checks also had intervals across zero. Jackknife intervals were much wider than secondary HAC intervals. These results do not establish linearity or rule out substantial curvature. Only 20 annual exposures per fit, selected records, missing visits and country weather limit inference. The package gives code, aggregate results, source hashes, a figure and independent arithmetic checks. External databases and record panels remain outside the bundle.

phenology · Orange-tip · temperature curvature · observation bias · regional replication · null result