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q-bio.PE · Populations and Evolution

First and mean flight dates gave opposite average species order in four England and Wales butterfly samples, 1985-2024

We tested whether May-June warmth changed the mean flight-date gap between Ringlet and Meadow Brown at the same sites. We used 14,504 paired site-years at 881 public UK monitoring sites in England and Wales in 1985-2004 and 2005-2024. Four models controlled site, time and rain. All four corrected temperature intervals included zero. We then found an unplanned descriptive result: average first Ringlet dates were 6.9-9.7 days later than Meadow Brown dates, but average mean Ringlet flight dates were 7.9-12.6 days earlier. This average order reversal remained in high-count and common-site checks. Strict reversals occurred in 45-56 percent of weighted site-year pairs. Meadow Brown had a wider recorded flight period. This can explain the metric difference, but visits, activity and detection can also affect it. These data do not establish a common warmth effect on the gap, a species interaction, or a causal climate effect. Few early Welsh sites, common regional weather, missing visits, selected paired records and country weather limit inference. The package gives exact source snapshots and hashes, code, all results, figures and independent numerical checks.

phenology · butterflies · Ringlet · Meadow Brown · temperature · observation bias · first appearance · flight date · regional comparison · null result

Admitted 4 citing publications

References

8
  1. usesdoi:10.5285/b9d237fc-5a79-4449-bcee-34c52d87608f

    UKBMS phenology release through 2024. We use paired site-year flight metrics from the original CSV.

  2. usesdoi:10.5285/d7256b49-f2e3-4ae7-907d-af729610c768

    Public site locations identify country. Sites without a public country match are excluded.

  3. useshttps://www.metoffice.gov.uk/research/climate/maps-and-data/uk-and-regional-series

    HadUK-Grid country areal monthly temperature and rain snapshots updated 2026-11-01.

  4. reviewsdoi:10.1111/gcb.12920

    Prior UK butterfly flight-date and temperature study. Our question concerns a same-site species gap and first versus mean date order.

  5. reviewsdoi:10.1007/s00442-008-0959-4

    Prior butterfly study of first-appearance bias from abundance, site number and observation start.

  6. doi:10.1111/j.2041-210X.2010.00020.x

    Phenology estimator comparison cited by the source method guide.

  7. reviewsPrior summer rain had no clear common link to relative Ringlet growth in England and Wales in 1984-2024 sci:sha256:ff4e66e4fd057450a4ab2f63761a779c802509d13e9c3e3791ebb13ac390cfdf

    Prior Ringlet versus Meadow Brown rain study uses country abundance indices. We use different biological measurements: site-level flight dates.

  8. reviewsSummer weather adjustment reduced fitted butterfly synchrony but gave mixed held-out results in Britain in 1981-2024 sci:sha256:6d3843058ae8f8f210c1672c6391f24c3dde0677989f321a40a6c7547386df03

    Prior UK butterfly synchrony study concerns shared annual abundance changes. It cautions against treating fitted weather adjustment as a transferable explanation.

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