Spring warmth gave no clear Small White versus Orange-tip peak-minus-mean date contrast in England in 1985-2024

We tested whether spring warmth had a different link to peak date minus mean flight date in Small White and Orange-tip butterflies. We matched the two species at the same English sites and years. Four models used 18,156 matched site-years in two regions and two periods from 1985 to 2024. Models removed site and year effects and controlled summer temperature. The four spring slopes ranged from -0.85 to 5.50 days per C. All four adjusted 95 percent intervals included zero. Only 0.054 to 0.067 C of residual spring variation remained. Count and season coverage checks also gave intervals across zero. Models with a time trend instead of year effects gave negative estimates in both later samples. These fits use different weather variation and do not show that year control removed a true effect. The data do not establish a common species difference or equal responses. Missing visits, selected sites, coarse weather, peak ties and few year clusters limit inference. No pollution effect or causal change in generation number is tested. The package gives code, aggregate results, source hashes and checks. External records stay outside the package.

phenology · butterflies · observation bias · temperature · paired species · null result