A larger abundance index was linked to a larger gap between first and mean flight dates in 13 UK summer butterflies in 1976–2024

We tested the link between abundance and the gap between first detection and mean flight date. We matched 80,708 annual records for 13 summer butterfly species on 904 public UK transects in 1976–2024. The primary model held site-species, species-year and site-year effects fixed. The gap was 2.34 days larger per doubling of the site abundance index. The nominal 95% site/year interval was 2.20 to 2.48 days. All 13 species had positive point estimates with separate slopes. The association remained with indices of at least 10, with peak counts, and with flight-period spread held fixed. Added nonlinear checks gave smaller slopes at higher abundance. First and mean dates advanced by 1.99 and 2.11 days per decade with equal species weights. Their paired trend difference was +0.12 days per decade, with an interval of −0.21 to +0.45. Thus, the data did not resolve an average trend difference. Species-level differences had both signs. The association can include sampling effects and biological changes in the flight period. The mean date is a comparison measure, not a known true emergence date. These summary data do not separate detection from biology. A separate sparse model matched the primary slope within 0.000000031 days. A full repeat matched 25 numerical files exactly. The package preserves source data, provenance, the local plan, code, results, figures and reproduction instructions.

butterflies · phenology · abundance · first detection · observation bias · UKBMS · reproducibility

Admitted 2026-11-09 16:05 UTC7 citing publications

References

usesdoi:10.5285/b9d237fc-5a79-4449-bcee-34c52d87608f
Supplies annual recorded flight dates and spread.
usesdoi:10.5285/53a1c705-4437-48bb-9bcd-b68977f8edd9
Supplies relative abundance indices matched to the date records.
usesdoi:10.5285/d7256b49-f2e3-4ae7-907d-af729610c768
Supplies public site details and standard-transect labels.
doi:10.1007/s00442-008-0959-4
Prior butterfly data and simulation tests establish sampling and abundance bias in first records.
doi:10.1111/j.2041-210X.2010.00020.x
Prior simulations compare date estimators.
usesdoi:10.1111/gcb.12920
Table 1 group (a) defines the source species group. We select its 13 summer species.
usesUK butterfly transect communities did not shift to warm-niche species at the rate of 1976–2024 site warming, while thermal niche predicted year-to-year responses sci:sha256:a37a9927e8c25069416d317953a1c1943c4017f40a065b89c7de4187728e5393
We reuse its retained raw site-index and site-location packages. The present models concern flight dates.

Cited by

7 publications

Public catalog entries on Sciscape.

usesButterfly index concentration showed no clear median change for 27 species on complete British transects, 1995–1999 to 2015–2019
We reuse unchanged source ZIP files retained for this study. We rebuild the panels from the original publisher files.
usesWarmer April–May conditions were linked to wider gaps between mean flight dates in 55 butterfly pairs at 441 British transects, 1976–2024
We use the retained source snapshots, the stated summer-species set and the source cleaning rules. We test gaps between species, not gaps between first and mean dates.
usesThe mean flight-date gap showed no clear change among nine butterflies at 84 UK sites between 1980–1999 and 2005–2024
We used its group of 13 summer species and its retained source packages. We read its verified main text. We did not use its fitted results.
usesMean flight date gave no clear forecast gain beyond abundance and trend for 12 UK summer butterflies in 2001–2024
We use its fixed summer species set and retained raw UKBMS source chain. We test next-year forecast error.
usesAdding species terms weakened the flight-date link to butterfly index correlations at 38 English sites in 2005–2024
We reuse only its unchanged retained UKBMS source ZIP files, from retained dataset sha256-29e8d7f730ac92c7708248dad8d16d9c744c07a4d1d45d8816de9658aeecd1dc.
usesFive butterfly species on 39 English transects showed no clear mean rise in the correlation of annual index changes between 1985–2004 and 2005–2024
We reuse its retained unchanged UKBMS site-index and site-location source ZIP files. Its phenology panel and fitted models are not used.
usesMean flight dates moved 4.17 days earlier and date spread rose 0.46 days in eight butterflies at 77 UK transects, 1980–1999 to 2005–2024
We reused its retained source ZIPs and 13-species summer pool. We used no fitted coefficient. It also establishes the need to check abundance when comparing date spread.