The rare Silver-spotted Skipper is extremely sensitive to small temperature fluctuations, a long-running study has revealed.
The skipper, a golden brown butterfly needs warm temperatures to thrive and the recent run of wet, cold summers has seen the butterfly struggle.
The study estimated changes in temperature across a range of Silver-spotted Skipper habitats and found that localised fluctuations in temperature lead to extreme fluctuations in the butterfly population size and in the probability of the skippers colonising new sites.
The Silver-spotted Skipper is restricted to South East England and has battled back from a dramatic decline in the 1950s thanks to conservation work.
Lead author Dr Jonathan Bennie from the University of Exeter explained: “Although we know that the climate overall is warming there is still much variability in the weather from one year to the next.
“This variability presents a threat to southern British butterflies that we might expect to take advantage of warmer conditions to colonise further north. In warmer years the silver-spotted skipper, which needs a balmy 25°C to become fully active, has expanded its range. However during the recent cold wet summers we have found the skipper clinging to the warmest south-facing hillsides waiting for better weather.”
The study used records of weather and butterflies since 1982, combined with computer modelling, to reconstruct how microclimates, created by different slopes and aspects, affect how many butterflies there were, where they were, and how quickly the species has been able to colonise new locations as the climate has warmed.
Co-author Dr Jenny Hodgson from the University of Liverpool said: "We were able to produce quite an accurate reconstruction of this butterfly's expansion across the landscape, and this makes us hopeful that we can provide useful predictions of which sites will be most important for conservation in the future."
The research indicates that conservation efforts could benefit from saving habitats with a range of different microclimates. Many species of butterfly are declining in Britain because of habitat loss, but the Silver-spotted Skipper has taken advantage of south facing slopes with warm microclimates. These provide vital refuges for the species during cooler summers; whereas in hotter summers north, east and west facing hillsides provide stepping stones of habitat that allow the species to spread through the landscape.
The research highlights that our increasing focus on landscape-scale conservation projects which seek to maintain habitat variety over large areas of the countryside, will be vital in helping butterflies to cope with the changing climate - Dr Tom Brereton, Butterfly Conservation Head of Monitoring
The study was funded by the Natural Environment Research Council (NERC) conducted by the University of Exeter in collaboration with the Universities of York and Liverpool, Butterfly Conservation, Sussex Wildlife Trust and the Centre for Ecology & Hydrology and was published in the journal Ecology Letters.