Record spring respite for rare butterflies

Last year’s record-breaking spring helped some of the UK’s rarest butterflies recover following years of decline, a scientific study today revealed. The hot, dry weather provided perfect conditions for early spring specialists enabling them to benefit from extended flight periods as they emerged weeks earlier than usual. The threatened Duke of Burgundy bucked a trend of recent declines as its population rose by 65% between 2010 and 2011. Other rare spring butterflies prospered — the Grizzled Skipper recorded a rise of 96% and the scarce Pearl-bordered Fritillary saw numbers jump by 103%.

Grizzled Skipper (Pete Eeles).

But despite last year’s much-needed respite, many of our most threatened butterflies remain in a state of long-term decline and need further targeted conservation work to turn their fortunes around permanently. Common garden species such as the Peacock, Small Tortoiseshell and Common Blue all recorded major population falls as the dry spring gave way to the coldest summer for 18 years. Summer-flying woodland specialists also struggled. The White Admiral recorded a 51% fall and the threatened Black Hairstreak, which recorded a substantial increase between 2009 and 2010, declined last year. Data was gathered by the UK Butterfly Monitoring Scheme (UKBMS) jointly led by Butterfly Conservation and the Centre for Ecology & Hydrology (CEH).

Black Hairstreak (Pete Eeles).

Some grass-feeding butterflies had a good year. The threatened Lulworth Skipper, confined to a small stretch of the Dorset coast, saw an 84% increase following years of decline and the Northern Brown Argus, found mainly in Scotland, saw a 21% rise. Migrant butterflies were recorded in good numbers. The Red Admiral saw a 123% increase and the Clouded Yellow recorded a rise of 41%.

Despite a number of species thriving in 2011 the overall picture for many butterflies is bleak. Almost three quarters of UK butterfly species have decreased in population during the last decade. Dr Tom Brereton, Head of Monitoring at Butterfly Conservation, said: “The great spring weather provided respite for our beleaguered butterflies but wide-ranging conservation efforts are needed to reverse long-term declines.”

UKBMS has run since 1976 and involves thousands of volunteers collecting data every week throughout the summer from more than 1000 sites across the UK. Dr Marc Botham from the CEH added: “Annual trends show us how strongly the day-to-day weather can affect butterfly populations in the short-term but the UKBMS dataset collected over 36 years reiterates the importance of long-term data in assessing the state of UK butterfly populations beyond these annual fluctuations. The high quality data of the UKBMS is attributable to the continuous support of thousands of volunteer recorders.” The UKBMS is operated by the Centre for Ecology & Hydrology and Butterfly Conservation and funded by a multi-agency consortium including the Countryside Council for Wales, Defra, the Joint Nature Conservation Committee, Forestry Commission, Natural England, the Natural Environment Research Council and Scottish Natural Heritage. The UKBMS is indebted to all volunteers who contribute data to the scheme.