Summer warmth gave no repeated positive link to growth spread in nine British butterflies in 1981-2024

We tested whether warmer summers had a wider spread of annual growth across nine butterfly species in England, Scotland and Wales. Six country and period models covered 1981-2002 and 2003-2024. Models controlled rain, prior summer weather, time and change in site count. Three temperature slopes were positive. Five six-test intervals included zero. Early Scotland had a negative slope of -0.0736 log10 growth-SD units per C, with an approximate corrected interval from -0.1184 to -0.0287. Its sign stayed negative after each species or year omission, but some species omissions and a median-based measure gave corrected intervals that included zero. Later Scotland did not clearly repeat the finding. These tests did not show a common positive association. They do not show no weather effect. Short samples, shared weather, selected species, unknown visits and source-index error limit inference. The package gives frozen inputs, source hashes, code, all results, numerical checks and a figure.

butterflies · weather · growth spread · observation bias · regional replication · UKBMS