Butterflies crash in fourth-worst year on record

UK butterflies suffered their fourth-worst year on record in 2016, with the majority of species experiencing a decline in numbers, a study has revealed.

A mild winter followed by a cold spring caused both rare and widespread species to struggle, despite many parts of the UK enjoying a warm and dry summer. Some 40 of the 57 species studied recorded a decline when compared with 2015.

The highly threatened Heath Fritillary had its worst year on record for the second year running, as numbers slumped by 27 per cent compared to 2015. This ongoing decline raises fears for the long-term future of the species, whose numbers have fallen by 82 per cent in the last decade alone.

Other species that fared badly included Grizzled Skipper, a spring-flying species that emerges from April, a month that was around a degree colder than the long-term average in 2016. Its struggles mirrored a bad year overall for skippers, all but one of the UK's eight species suffering a fall in numbers compared to 2015. White Admiral, White-letter Hairstreak and Grayling slumped by 59 per cent, 42 per cent and 27 per cent respectively, while more widespread species also struggled: Wall was down 31 per cent, Gatekeeper down 48 per cent and Meadow Brown fell by 31 per cent when compared with 2015.

Heath Fritillary suffered its worst year on record in 2016 (Photo: Richard Bonser)

Research suggests that the UK's increasingly mild winters are having a negative effect on butterflies as they may lead to increased disease, predation or disruption of overwintering behaviour. Cold springs can also cause problems for butterflies by reducing or delaying emergence leading to shortened lifespans.

Some species bucked the trend to record reasonable years. The previously extinct Large Blue, one of the UK's rarest butterflies, recorded its second best year on record with numbers up 38 per cent on 2015. The butterfly has responded to conservation work to improve the specific grassland habitat that it relies upon to thrive, and has shown a significantly increasing population trend since its reintroduction in 1983. The widespread and migratory Red Admiral recorded a rise of 86 per cent compared to 2015, and Clouded Yellow, another mainly migrant species, saw its numbers rise by 35 per cent.

The largely migrant Clouded Yellow was one of the few species to fare well in 2016 (Photo: Bob Eade)

Professor Tom Brereton, Head of Monitoring at Butterfly Conservation, said: "Worryingly, not even the pleasant summer weather of 2016 was enough to help butterflies bounce back from a run of poor years.

"The results show that butterflies are failing to cope with our changing climate and how we manage the environment. As butterflies are regarded as good indicators of environmental health this is hugely concerning for both wildlife and people."

Dr Marc Botham, Butterfly Ecologist at the Centre for Ecology & Hydrology, said: "The weather at critical times of species development can cause dramatic changes in population numbers in the short term. What is of greatest concern is the regularity with which these short-term changes in recent years are negative, resulting in significant long-term declines for many species.

"Furthermore, this is becoming more and more commonplace for many of our most widespread and abundant species equating to large reductions in overall butterfly numbers with knock-on effects to their ecosystems."

Sarah Harris, Breeding Bird Survey (BBS) National organiser at the British Trust for Ornithology, commented: "Our understanding of just how our butterflies are doing would be much poorer without the huge amount of effort our volunteers put in. The data they collect allow us, working alongside our partners, to monitor the UK's butterflies in the detailed and long-term way we do, and bring attention to those species in trouble and those enjoying conservation success, as seen in the Large Blue. Thanks must go to all who contributed."

Anna Robinson, Monitoring Ecologist at the JNCC, added: "We are really grateful to the thousands of volunteers who get involved in monitoring the UK's butterflies. The evidence provided by the UKBMS is of great importance in showing the need for conservation action to improve the situation."

The UKBMS has run since 1976 and involves thousands of volunteers collecting data through the summer. Last year a record 2,507 sites were monitored across the UK. The scheme is organised and funded by Butterfly Conservation, the Centre for Ecology & Hydrology, the British Trust for Ornithology and the Joint Nature Conservation Committee. For more information, please visit www.ukbms.org