One of the UK’s rarest butterflies has recorded its best year for a decade thanks to 2014’s warm spring weather and work to restore its habitat, a study has revealed.

Last year the critically endangered High Brown Fritillary experienced its best season since 2004 with numbers increasing by more than 180% compared to 2013, the UK Butterfly Monitoring Scheme (UKBMS) led by Butterfly Conservation (BC) and the Centre for Ecology and Hydrology (CEH) found.

The striking orange and black butterfly once bred in most large woods in England and Wales but habitat loss has resulted in alarming declines raising fears that it could be heading toward extinction in the UK.

The High Brown Fritillary, one of only two critically endangered butterflies in the UK, is now restricted to a handful of colonies in North West and South West England and one in Wales.

The butterfly benefitted from warm spring weather and work by wildlife charity Butterfly Conservation and partners targeted at restoring its habitat. 

Elsewhere, the warmer than average spring and early summer saw many butterflies thrive with the Marbled White, Ringlet and Brimstone all experiencing their best years since the UKBMS began in 1976.
Orange-tip and Speckled Wood had their fourth best years on record and the threatened Duke of Burgundy rallied with a 26% increase in numbers compared to 2013.

The UK’s skipper butterflies fared well especially those that peak in abundance during early to mid-summer, with all seven species studied showing an annual increase.

The Large Skipper was up 86% compared to 2013 and the rare Lulworth Skipper saw numbers climb by 15%. More than half of the 56 species studied saw their numbers rise compared to 2013.

The warm start to the summer gave way to colder conditions later in the year which resulted in the butterfly season peaking slightly earlier in July rather than August which was colder and wetter than average.

Last year’s losers included the ‘cabbage white’ butterflies with the Small White down 66% compared to 2013 and the Large White declining 69% for the same recording period.

Some butterflies associated with high summer also struggled in the cold August weather with the Chalk Hill Blue numbers down 55% compared to 2013 and Adonis Blue down 43%.

Dr Tom Brereton, Head of Monitoring at Butterfly Conservation, said: “The High Brown Fritillary is one of only two butterflies classed as critically endangered in the UK so it is fantastic news that numbers are at their highest level for more than a decade. 

“A huge amount of work co-ordinated by Butterfly Conservation has been put into conserving this butterfly in recent years, especially though wildlife-friendly farming schemes, so the results will come as a welcome boost to all involved.

“There is a long way to go before the long-term decline has been reversed, with ongoing targeted conservation efforts crucial in this.”

The UKBMS has run since 1976 and involves thousands of volunteers collecting data through the summer from around 2,250 sites across the UK.

The UKBMS is run by Butterfly Conservation, the Centre for Ecology and Hydrology, and the British Trust for Ornithology, in partnership with the Joint Nature Conservation Committee, and supported and steered by Forestry Commission, Natural England, Natural Resources Wales, Northern Ireland Environment Agency, and Scottish Natural Heritage. The UKBMS is indebted to all volunteers who contribute data to the scheme.