Spring rain slopes for Orange-tip flight balance had no clear period change at shared sites in England and Wales, 1985-2024

We tested whether April-May rain slopes for Orange-tip flight balance changed between 1985-2004 and 2005-2024. Sites needed five valid years in each period. Site-by-period models used 6,789 records at 259 English sites and 102 records at four Welsh sites. The later-minus-earlier slope was -1.46 days per 100 mm in England, with a two-country adjusted 95 percent interval of -3.98 to +1.06. The Welsh estimate was +2.75, with interval -6.59 to +12.08. All planned sensitivity intervals included zero. These results do not establish equal slopes. They show no clear period change under the tested model. Missing visits, selected persistent sites, coarse weather and very few Welsh sites limit inference. Rain can change both biology and observation. This is not a causal climate or pollution result. The package gives code, aggregate results, a figure and exact external source hashes.

phenology · Orange-tip · rainfall · period change · observation bias · shared sites