2020 has been hailed as a “good” year for butterflies – but conservationists warn that our view of the “good” may change.
While the past year may have been particularly difficult for humans, 2020 was officially a “good” year for butterflies according to the latest results from the UK’s Annual Butterfly Monitoring System (UKBMS), led by Butterfly Conservation, the UK’s Center for Ecology and Hydrology ( UKCEH), British Trust for Ornithology (BTO) and Joint Nature Conservation Committee (JNCC). However, while the decline in butterflies continues, conservationists ponder how our view of what makes a good year has changed.
Dr. Richard Fox, Assistant Director of Recording and Monitoring at Butterfly Conservation, explains, “Perhaps due to the warm, sunny spring weather last year and the fact that more people than ever have enjoyed the outdoors as part of their daily activities, butterflies seemed more numerous. In fact, our basic experience of nature around us has changed over time.
“The carefully collected UKBMS data shows that it was the third good year in a row for butterflies in the UK and tenth place (averaged across all species) since the program began in 1976. Nevertheless, almost half of our butterfly species (27 of 58 species) were registered in below-average numbers last year.
Silver-trimmed blue, Copyright Andy Adcock, from the Surfbirds Galleries
“It is worrying that the population of so many butterfly species has continued to decline after three good years compared to 40 years ago. Just under a third (31%) of the butterfly species assessed in the UK show a long-term decline.
“We must be careful about postponing the basic syndrome, forgetting (or never experiencing) the greater biodiversity that has occurred in Britain in previous decades and therefore lowering our expectations and aspirations for conservation. This is where the UKBMS plays an important role in showing how insect populations have declined over time. “
Butterfly populations naturally fluctuate from year to year, but long-term trends in British butterflies are largely determined by human activities, particularly habitat destruction and climate change. Conservation efforts can make a real difference for local people, and 2020 was a good year for a number of rare species targeted conservation efforts, including Large Blue (with the second best common year) and Silver-Spotted Skipper (with which they do was) his third best year), silver occupied blue (joint fourth best year) and Duke of Burgundy (joint sixth best year).
Among the UK’s widespread butterfly species, Brimstone, Orange-tip and Marbled White all had a good year, although their numbers weren’t at the exceptional levels of 2019. After four very bad years, small tortoiseshell numbers improved, showing a 103% increase from 2019, but remains below the long-term average, and the species have still seen a sharp decrease in abundance (79%) since 1976.
One species that had a particularly bad year was the little mother-of-pearl butterfly. In 2020, this butterfly experienced its third worst year on record, extending nine consecutive years with below-average numbers. Small mother-of-pearl butterfly populations have declined by 68% since the UKBMS began recording in 1976. The migrant Painted Lady also had a bad year, and the Wall, Grayling, and Small Skipper populations all remained low.
Dr. Marc Botham, Butterfly Ecologist at the UK Center for Ecology and Hydrology, said, “While 2020 is a challenging year for data collection and maintenance, we received nearly half a million records from more than 2,500 locations over the course of the year.
“We are incredibly grateful to the thousands of volunteers who have been able to conduct COVID-safe surveillance and maintain this invaluable long-term data set. In this way, scientists can better assess how butterflies are doing and how the health of our landscape in general is. Thanks to the efforts and progress of the volunteers in analytical methods, we were able to report on the population of all but one of our British butterfly species in 2020. “
Sarah Harris, national organizer of the British Trust for Ornithology’s breeding bird survey, whose volunteers are collecting butterfly data as part of the butterfly survey in larger countries, said: “While 2020 has been an overall good year for British butterflies, the latest results underscore the value of long-term term monitoring as this data shows the effects of habitat loss and climate change. Butterflies are an important part of our ecosystems that so many birds, mammals, and other species rely on, and this data is so valuable to our understanding of the health of the natural environment.
“Thanks to the volunteers, we are able to monitor butterfly populations and hundreds of BTO / JNCC / RSPB breeding bird survey volunteers are revisiting their bird record squares to survey butterflies, moths and dragonflies for butterfly survey across the country. We are grateful to all of the volunteers who helped compile records for the UKBMS and we look forward to being part of this important oversight. “
All data for UKBMS 2020 can be found here: UKBMS.org/official-statistics