May-June warmth gave no clear repeated link to three-species flight-date spread in England and Wales in 1985-2024

We tested whether May-June warmth changed the spread of mean flight dates among Gatekeeper, Meadow Brown and Ringlet at the same sites. Four models used 9,951 site-years at 602 sites in England and Wales in 1985-2004 and 2005-2024. Models controlled site, time and rain, with equal total year weights. All four corrected temperature intervals include both signs. Slopes range from -0.03 to +0.27 days per C. The group mean date was earlier in warmer years. Count filters and common English sites did not establish a spread response. A March-May alternative gave positive slopes with intervals above zero in both later samples, but not in either early sample. Few Welsh sites, shared country weather, missing visits and co-detection selection limit inference. The result does not show equal species responses, stable full flight overlap or a causal climate effect. The package includes raw sources, hashes, the complete panel, code, figures and independent numerical checks.

phenology · butterflies · temperature · relative timing · observation bias · regional replication · null result