The State of the UK's Butterflies 2015 was launched yesterday at an evenat at ZSL London Zoo. The report, by Butterfly Conservation and the Centre for Ecology & Hydrology (CEH), found that 76% of the UK's resident and regular migrant butterflies declined in abundance, occurrence or both over the last four decades. It also found that a number of widespread species such as Wall, Essex Skipper and Small Heath now rank among the most severely declining butterflies in the UK.
On the other hand, the findings also reveal that intensive conservation efforts have started to turn around the fortunes of some of the UK's most endangered butterflies. During the last ten years the numbers of the threatened Duke of Burgundy have increased by 67% and Pearl-bordered Fritillary has experienced a 45% rise in abundance. Dingy Skipper and Silver-studded Blue have shown 21% and 19% increases in occurrence respectively and even the UK's most endangered butterfly, High Brown Fritillary, has been relatively stable over the past decade. But despite breakthroughs with some threatened butterflies, the report revealed that other species continue to struggle. The long-term declines of the Wood White, White Admiral and Marsh Fritillary show few signs of stopping.
The report found that some once common and widespread species have become a cause for concern. The Wall, once a common farmland butterfly across southern Britain, has suffered a 36% fall in occurrence and 25% drop in abundance since 2005, continuing a longer trend of decline. One of our most abundant species, Gatekeeper, has experienced a 44% decline in abundance in the last decade and numbers of Small Skipper have been below average in every year of the 21st century.
The deterioration of suitable habitats due to agricultural intensification and changing woodland management are seen as major causes of the decline of butterflies that are habitat specialists. Decreases of butterflies found in the wider countryside are less well understood; climate change and pesticides may be playing a more harmful role in their declines than previously thought.
The report reveals a north–south split among butterflies of the wider countryside, with species in England declining and those in Scotland showing no long-term trend. Less severe habitat damage in the north and the differing geographical effects of climate change are believed to be behind the split.
The report reveals that more butterflies are reaching the UK from overseas. Since the 1970s the three common migrant species — Clouded Yellow, Red Admiral and Painted Lady — have all increased dramatically in abundance. In the last few years rare migrants such Scarce Tortoiseshell and Long-tailed Blue have arrived in unprecedented numbers.
Butterfly Conservation Vice-president Chris Packham said: "This report reveals that UK butterflies are in real trouble. Yet again we are presented with sobering evidence that our much-cherished wildlife is in dire straits.
"As a society we are guilty of standing idly by as once common species, never mind the rarities, suffer staggering declines. This is a situation that should shame us all. The future of the UK's butterflies does not have to be bleak. This report shows conservation work can and does turn around the fortunes of our most threatened butterflies."
Richard Fox, lead report author and Butterfly Conservation's Head of Recording, added: "Thanks to tens of thousands of people who help to count butterflies in the UK each year, we have a clear picture of the changing fortunes of these captivating insects.
"Overall the situation is stark. Most butterflies have decreased since the 1970s and an alarming number of common species have declined severely. On the other hand, trends over the past decade provide grounds for optimism and show that our approach to conserving threatened butterflies can stem and even reverse declines."
David Roy, who led the CEH contribution to the report said: "We've used sophisticated analyses for this latest report, revealing major declines. This is of great concern not just for butterflies but for other wildlife species that share the same habitats. The findings act as a barometer of the overall state of the environment."
The report comes from data gathered by two long-running citizen science projects — the Butterflies for the New Millennium (BNM) recording scheme and the UK Butterfly Monitoring Scheme (UKBMS).