Some of Britain’s most threatened butterflies are bouncing back after decades of decline, according to a new study.
This may be due to more open woodland and even climate change for some species.The brown argus has moved into new areas and north west as it has shifted to feeding from a species of geranium that has become more widely available as the climate warms.
Although butterflies remain in long term decline, last year three quarters of at-risk species saw an increase in numbers, including rare species like the wood white and the marsh fritillary. Experts said the improvement in the butterflies’ fortunes was likely to be the result of targeted conservation action, such as leaving open glades in woods where flowers can grow, and better weather in 2010 after three disasterous wet summers. Dr Tom Brereton, head of monitoring at Butterfly Conservation, that compiled the latest figures, said buterflies are extremely sensitive to changes in the weather. But last year saw a warm summer for successful feeding, while a cold winter in 2009/2010 will have helped check parasites and stop butterflies emerging too early, helping the insects breed successfully. He even said climate change could be benefitting some species as the weather is warmer, although many butterflies suffer, like the mountain ringlet, as they need cold climes and the change is too rapid for most to adapt. The brown argus has moved into new areas and north west as it has shifted to feeding from a species of geranium that has become more widely available as the climate warms. “Some species, including some of the specialists, are benefitting from climate change,” he said. In the long term butterfly numbers continue to decline, with three quarters of the nearly 60 species found in Britain seeing numbers fall in recent decades and nearly half of them seriously threatened. One of the UK’s rarest butterflies, the Lulworth skipper, which is confined areas on the Dorset coast, had its worst year since the monitoring scheme began in 1976, and there are concerns that managing landscapes to benefit other species may be harming the butterfly. A lot of sites have been grazed to benefit wild flowers and other butterflies but the Lulworth skipper needs long grass and wild areas. Meadow browns, one of the country’s most common species, also had its worst year on record, while Essex skippers, small skippers and wall butterflies also fared badly. However in the short term three quarters saw an increase in numbers in 2010 on 2009 levels. The wood white, which has suffered a 96 per cent decline since the 1970s, saw numbers increase last year by 600 per cent, while the marsh fritillary, in decline since the 1950s, more than doubled its numbers from 2009 to 2010.