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UK butterflies

Threatened butterfly species cope well in below-average butterfly year
Close-up of a male silver-studded blue butterfly

At a time when much of the natural world is in crisis, some butterfly species are showing signs of recovery – likely the result of concentrated conservation effort and positive land management.

Results from the annual UK Butterfly Monitoring Scheme (UKBMS) – led by Butterfly Conservation, the UK Centre for Ecology & Hydrology (UKCEH), British Trust for Ornithology (BTO) and Joint Nature Conservation Committee (JNCC) – show that while the overall picture for butterflies in 2021 was poor, species that are the focus of targeted conservation efforts have fared well.

A below-average year

After three good years in a row, 2021 was a below-average year for UK butterflies, and the worst since 2017.

Following one of the coldest and wettest Mays on record, especially in England and Wales, many common and widespread species did poorly.

The green-veined white had its fourth-worst year on record and large skipper its fifth-worst. The common blue, large white and small skipper also had a poor year.

Even some widespread species that have shown long-term increases fared badly in 2021, with the ringlet recording its lowest numbers since 2012.

Promising signs for threatened species

Despite the context of the generally poor year, there were some promising results for many threatened species.

The endangered heath fritillary, which has been the focus of long-term intensive conservation efforts in Kent, Essex and Somerset, had a good year and has now increased 112% at monitored sites in the last decade.

The meticulously gathered UKBMS data show that 2021 was also a good year for the silver-studded blue (main image), a butterfly that is classed as vulnerable in Britain.

It is another species that has benefitted from much conservation work on its heathland and grassland habitats. 2021 was its best year since 1996 and its numbers have increased by 70% at monitored sites since the 1970s, with it having six above average years in a row.

Differences around the UK

2021 was a poor year for butterflies in England, ranking 33rd out of the 46 years since the UKBMS began.

It was a particularly terrible year for green-veined white – one of our most widespread butterfly species – which suffered its joint-third worst year since 1976. White admiral also had its third-worst year on record and its populations have now decreased by 62% in England since the UKBMS began.

Scotland was the only UK country in which butterflies fared well overall in 2021, with more species increasing than decreasing from 2020 levels. The year ranked 10th out of 43 years with UKBMS monitoring data in Scotland.

The year 2021 was an average year for butterflies in Wales, ranking 24th out of 46 years since monitoring began.

It was also an average year for butterflies in Northern Ireland, ranking 10th of the 18 years for which trends can be calculated.

‘We’re delighted to be seeing some positive signs for species such as the heath fritillary, especially when the general long-term picture for UK butterflies is one of great decline. It reinforces the importance of managing and restoring habitat in a way that supports the survival of our butterflies. While the heath fritillary remains a priority for conservation, these successes demonstrate what can be achieved through dedicated long-term conservation effort.

‘There are grounds for cautious optimism in the results of many other threatened species that are the focus of conservation action, especially given that 2021 wasn’t a good year for butterflies in general. The Black and Brown Hairstreaks both had a good year in 2021, the latter its best since 1996, as did Glanville Fritillary, Dingy Skipper, Adonis Blue and Chalk Hill Blue, all of which were above their long-term average abundance.’

Butterfly Conservation’s associate director of recording and monitoring

Identifying at-risk species

The efforts of Butterfly Conservation, along with other organisations, volunteers and landowners are providing resilience for threatened butterflies in years, such as 2021, when poor weather is a problem for most species.

But there is much more to do, and the UKBMS data help target those species most in need of conservation work.

Many species still show major long-term decline; white admiral had a terrible 2021, recording its third-worst year since 1976 at monitored sites, with all three worst years taking place in the last decade.

Pearl-bordered and small pearl-bordered fritillary also both continued at low levels, well below their long-term averages.

Progress towards biodiversity targets

Butterfly populations fluctuate naturally from year to year, largely due to the weather, but the long-term trends of UK butterflies are mainly driven by human activity, particularly the deterioration of habitats due to inappropriate management and pollution, and climate change.

Conservation efforts can make a real difference to local populations and working on threatened species in key landscapes to deliver nature recovery is a priority.

‘Despite 2021 continuing to be a challenging year for data gathering and conservation activity, we received 476,000 records from more than 2,900 sites over the year, including a record number of standard transects.

‘We are incredibly grateful to the thousands of volunteers who were able to carry out monitoring and maintain this invaluable long-term dataset. This enables scientists to measure how butterflies are faring as well as assessing the health of our countryside generally. The UKBMS data are vital in assessing the effectiveness of government policies and progress towards the UK’s biodiversity targets.’

Butterfly ecologist at the UK Centre for Ecology & Hydrology

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