The UK Government has published indicators on butterflies in the United Kingdom, which are intended to contribute to a suite of indicators due to be updated later this year (the UK Biodiversity Indicators).
In the meantime, the specific indicators on butterflies from earlier data has been published ahead of the overall UK Biodiversity Indicators.
The current publication uses two measures of annual butterfly population abundance are presented within the documents:
- The first for specialist butterflies (species strongly associated with semi-natural habitats such as unimproved grassland), and;
- The second for butterflies found in both semi-natural habitats and the wider countryside.
The measures are multi-species indices compiled by Butterfly Conservation (BC), the Centre for Ecology & Hydrology (CEH), and the Joint Nature Conservation Committee (JNCC) from data collated through the UK Butterfly Monitoring Scheme (UK BMS) and the Wider Countryside Butterfly Survey (WCBS).
The indicators use data from butterfly transect sites on farmland and in woodland from the UK BMS and additionally randomly selected farmland plots from the WCBS.
The four headline points from the report are:
- Since 1976, the habitat specialists butterflies index has fallen by 77%.
- Over the same period, the index for species of the wider countryside has fallen by 46%.
- Large fluctuations in numbers between years are a typical feature of butterfly populations, principally in response to weather conditions. 2017 was a relatively bad year for butterflies; the fourth worst in the 42-year series and it was likely due to periods of poor weather during the spring and summer months.
- The statistical assessment of change is made on an analysis of the underlying smoothed trends. Since 1976, populations of habitat specialists and species of the wider countryside have declined significantly but both trends show no significant change since 2012.
The four key published documents covering the butterfly survey between 1976 to 2017 can can be downloaded from the following web-links:
- If you are looking to develop metrics for biodiversity or, generally, want to encourage biodiversity then you should download the updated indicators from 1976 to 2017.
- Consider the development of biodiversity metrics or programmes to encourage biodiversity using the update indicators.
- Review any further publication of biodiversity indicators related to butterflies expected to be published by the UK Government in the Summer 2019.