Spring warmth slopes for peak minus mean Orange-tip dates had opposite signs in Wales in 1985-2024

We tested whether March-April warmth was linked to peak-count date minus mean flight date of Orange-tip butterflies. Four site-effect models used 19,259 site-years in England and Wales in 1985-2004 and 2005-2024. Models controlled winter temperature, spring rain, time and peak count. Each year had equal total weight. England slopes were -0.22 and -0.06 days per C; both four-test adjusted 95 percent intervals included zero. Wales slopes were +1.55 and -0.80 days per C, with adjusted intervals of +0.10 to +2.99 and -1.36 to -0.24. Thus the two Welsh estimates had opposite signs. Some filters gave intervals across zero. The early Welsh sample had 98 site-years at eight sites. Missing visits, peak ties, selected sites, coarse weather and 20 annual exposures per fit limit inference. These results do not establish a stable change in flight-curve shape or a causal climate-change effect. The package gives code, source hashes, aggregate results, a figure and numerical checks. External record data remain outside the bundle.

phenology · Orange-tip · temperature · observation bias · UKBMS · regional replication