April-June warmth gave no clear repeated link to the Ringlet and Meadow Brown flight-date gap in England and Wales, 1980-2024

We tested whether warmer April-June weather changed the gap between Ringlet and Meadow Brown mean flight dates at the same sites. Four site-effect models used 17,204 paired site-years in England and Wales in 1980-2001 and 2002-2024. They controlled rain and a linear time trend. Gap slopes were -1.17, -0.29, -1.97 and -0.72 days per C. All four corrected intervals included zero. Thus, the models did not establish a repeated nonzero link. First-record date slopes were positive in all four samples, but corrected intervals for the difference between date measures also included zero. Count filters, count controls, repeated-site filters and equal year weights kept all mean-date point estimates negative. Country weather was strongly correlated. The early Wales sample had only eight sites. Missing visits, count error, selected sites and coarse weather limit inference. The result does not identify a causal climate effect, ecological harm or a pollution effect. The package gives a paired evidence table, exact source hashes, code, figures and offline checks.

butterflies · phenology · temperature · observation bias · paired sites · regional replication · null result