May-June warmth gave no clear repeated link to Meadow Brown flight spread in England and Wales in 1985-2024

We tested whether May-June warmth changed Meadow Brown flight-date spread in England and Wales in 1985-2004 and 2005-2024. Four site-intercept models used 15,225 site-years at 936 public sites. Models controlled rain and time and gave each year equal weight. Flight-date standard deviation slopes were +0.66, +0.58, +0.70 and +0.39 days per C. Only early England had an interval above zero after correction for four tests. Thus, a repeated nonzero link was not established. All point estimates stayed positive after each year omission and in the planned sensitivity checks. Peak-count adjustment had little effect in England but reduced the later Welsh estimate. Country weather correlation, few early Welsh sites, selected records and missing visit-level effort limit inference. These estimates do not show a causal temperature effect or longer individual life. The package gives the full derived panel, source hashes, code, all fits, a figure and independent numerical checks.

phenology · butterflies · Meadow Brown · flight duration · temperature · observation bias · regional replication · null result