United Kingdom Butterfly Monitoring Scheme: site indices 2023
type: Dataset
description: This dataset comprises individual site indices for UK butterfly species calculated from data from the UK Butterfly Monitoring Scheme (UKBMS). Site indices are a relative rather than an absolute measure of the size of a population, and have been shown to relate closely to other, more intensive, measures of population size such as mark, release, recapture (MRR) methods. The site index can be thought of as a relative measure of the population size, being a more or less constant proportion of the number of butterflies present. The proportion seen is likely to vary according to species; some butterfly species are more conspicuous and thus more easily detected, whereas others are much less easy to see. Site indices are only calculated at sites with sufficient monitoring visits throughout the season, or for targeted reduced effort surveys (timed observations, larval web counts and egg counts) where counts are generally obtained as close to the peak of the flight period as possible and are subsequently adjusted for the time of year and size of the site (area of suitable habitat type for a given species). Wider Countryside Butterfly Survey (WCBS) sites are thus excluded because they are based on very few visits from which indices of abundance are not calculated. For transect sites, a statistical model (a General Additive Model, 'GAM') is used to impute missing values and to calculate a site index. Each year most transect sites (over 90%) produce an index for at least one species and in recent years site indices have been calculated for over 2,000 sites across the UK. Site indices are subsequently collated to contribute to the overall 'Collated Index' for each species, which are relative measures of the abundance of each species across a geographical area, for example, across the whole UK or at country level for England, Scotland, Wales or Northern Ireland. Individual site indices are important in informing conservation management as not all sites show the same patterns for e…
keyword: England
keyword: Environmental Monitoring Facilities
keyword: Monitoring
keyword: Northern Ireland
keyword: Observation systems
keyword: Scotland
keyword: UK-SCAPE
keyword: United Kingdom
keyword: Wales
issued: 2025-01-26T22:42:36.936718
modified: 2026-07-30T22:15:42.487562
spatial: Location
  geometry: {"type": "Polygon", "coordinates": [[[1.768, 49.124], [-9.272, 49.124], [-9.272, 60.861], [1.768, 60.861], [1.768, 49.124]]]}

Environmental Information Data Centre
type: Organization

Download the data
type: Distribution
description: Download a copy of this data
access URL: https://data-package.ceh.ac.uk/data/04857889-1b09-40ff-a87e-71eb6ac2e998
issued: 2026-07-30T22:15:42.544070
modified: 2026-07-30T22:15:42.493214

Supporting information
type: Distribution
description: Supporting information available to assist in re-use of this dataset
media type: application/zip
format: ZIP
access URL: https://data-package.ceh.ac.uk/sd/04857889-1b09-40ff-a87e-71eb6ac2e998.zip
issued: 2026-07-30T22:15:42.544072
modified: 2026-07-30T22:15:42.493288