Some of the UK’s most endangered butterflies have had a bad year in 2021 thanks to conservation efforts, the results of the annual survey have shown.
The wood-loving heather fritillary has doubled in abundance over the past decade, although it is 90% below 1980 levels. The silver-studded blue has also done well, recording its best year since 1996.
Restoring lost habitats has allowed these species to do well despite bad weather, including a cold and rainy May in England. The UK Butterfly Monitoring Program, comprising nearly half a million records, showed 2021 to be a tough year for overall butterfly abundance, ranking 28th out of 46 years in records dating back to 1976.
Many common species struggled, including the green-veined white, which had its fourth-worst year on record, and the large skipper, which had its fifth-worst year. Even some widespread species that have increased over the long term have fared poorly, with the satyr recording its lowest numbers since 2012.
“We are delighted to see positive signs for species such as heather fritillaria, particularly when the overall long-term picture for British butterflies is one of significant decline,” said Richard Fox, ecologist at Butterfly Conservation. . “This reinforces the importance of habitat management and restoration. The heather fritillaria is a good example of a species that would almost certainly be extinct in Britain by now, were it not for conservation efforts.
These efforts include recreating the wooded glades that were once common when people practiced coppicing. “There are also grounds for cautious optimism in the results of many other threatened species that are the subject of conservation action,” Fox said. “Black and brown hair highlights both had a strong year in 2021, as did glanville fritillary, dull skipper, adonis blue and chalk hill blue.”
the UK Butterfly Monitoring Program uses data collected by volunteers from over 2,900 sites across the UK. Weather permitting, butterfly watchers travel a specific route each week from April through September.
Butterfly populations naturally fluctuate from year to year, largely due to weather conditions. Adult insects need hot, dry weather to fly, while caterpillars need to avoid drought, which can kill the plants they feed on.
“They are cold-blooded creatures that rely on the sun’s heat to warm up and become active,” Fox said. “So if it’s really cold, they can’t fly, feed or find a mate. The incredibly bad month of May will have had an impact on certain butterflies which were then in the adult stage, such as the blue holly.
Long-term trends for British butterflies are mainly driven by human activity, in particular the destruction and degradation of natural habitats by intensive agriculture. Of the 54 species with long-term records in England, 20 show declines and 12 are more abundant. The bead- and bead-lined fritillary, for example, is only a third of its 1970s level.
“Mass destruction of natural habitat has largely come to a halt in the UK,” Fox said. “But there is continued habitat deterioration, even in nature reserves.” This was caused by lack of funding as well as pollution and pesticides from agriculture, he said.
Scotland bucks the trend, with 12 monitored species showing long-term increases in abundance, compared to three showing long-term declines. “The main reason is that there’s a whole bunch of butterfly species that are spreading north with climate change,” Fox said.
Sarah Harris, from the British Trust for Ornithology, whose volunteers also collect butterfly data, said: ‘Butterfly species are indicators of the health of our natural environment and can therefore also be used to help understand and protect the wider ecosystem on which so many birds, mammals and other species depend.