Fears grow for some of Britain's rarest butterflies

05 March 2010

Five of Britain's rarest butterflies face a growing risk of extinction, according to analysis of new figures for butterfly sightings in 2009. The numbers of the species in question, the Duke of Burgundy, High Brown Fritillary, Wood White, Lulworth Skipper and Pearl-bordered Fritillary, either continued to fall, or remained at near rock-bottom levels during the last year.

Concern for the future of these butterflies follows analysis of data collected by the UK Butterfly Monitoring Scheme (UKBMS) from more than a thousand sites nationwide. The scheme is coordinated by the Centre for Ecology & Hydrology (CEH), and the charity Butterfly Conservation.

Conservationists are particularly concerned about the Duke of Burgundy, which has reached new low points in each of the past three summers and is now at its lowest level since monitoring began. The butterfly, which 50 years ago was a common sight in woodland clearings, now has fewer than 80 colonies throughout the whole of the UK.

The High Brown Fritillary remained at very low levels in 2009, with fewer than 50 colonies, while the Wood White and the Lulworth Skipper each had under 100 colonies. The Pearl-bordered Fritillary had its second worst year in 2009.

Experts believe that the extremely wet weather throughout the summers of 2007 and 2008, followed by above average rainfall in July and August 2009, have accelerated a long-term decline in numbers. Heavy rain makes it hard for butterflies to survive.

Butterflies are important as indicators, alerting us to underlying problems with the environment. If butterfly numbers are falling, inevitably other wildlife is in decline. The main factors causing the long-term decline of many butterfly species include the loss of crucial habitats such as flower-rich grassland and the intensification of farming methods. A lack of management is also causing problems in habitats such as woodlands.

The 2009 figures show that some relatively common butterflies also had a tough time. According to the data, species such as the Wall Brown, Small Skipper and Green Hairstreak remained at very low numbers in 2009. But the Small Tortoiseshell, which has suffered a serious decline in recent years, made a slight comeback.

A highlight of 2009 was the massive migration of Painted Lady butterflies, which originated in North Africa and arrived in vast swarms in early summer. At one point, it was estimated there could have been over a billion Painted Ladies in the UK. However the UKBMS figures indicate that this migration was not quite on the scale of the last big one in 1996.

Overall, the figures show a modest recovery compared with statistics from the summer of 2008, which was the worst for 25 years. In addition to the abundance of the Painted Lady, some native butterflies also did well in 2009. These included the Green-veined White, Ringlet and Speckled Wood, all of which thrive in lush woodland areas and may have been beneficiaries of the damp but not particularly cold conditions.

Dr Tom Brereton, Head of Monitoring with Butterfly Conservation, said they were particularly concerned about the Duke of Burgundy. "At the start of the century there were about 200 colonies in the country. This number has now more than halved - and most colonies that remain are small. It is a serious situation."

Each year the UKBMS collates data collected by hundreds of volunteers nationwide. Dr Marc Botham, a butterfly ecologist with the Centre for Ecology & Hydrology, who analysed the data, said the results showed the enormous value of long running datasets in identifying environmental problems.

"We are extremely grateful to the many volunteers who contribute each year," he said. "Through their efforts a new milestone was reached in 2009 when the number of sites monitored passed the one thousand mark for the first time."

More: http://www.ceh.ac.uk/news/news_archive/2010_news_item_06.html