Last year was a good year for UK butterflies, experts have said – but warned that long-term declines of wildlife mean the view of what is “good” is shifting.
Results from the annual UK Butterfly Monitoring Scheme (UKBMS) showed 2020 was the third good year in a row for British butterflies, ranking the 10th best since the scheme began in 1976 on average across all species.
But despite the good result in the wake of a warm, sunny spring, almost half the UK’s butterflies – some 27 out of the 58 species monitored – recorded below-average numbers last year.
It has prompted a warning over “shifting baseline syndrome”, where people forget – or have never experienced – the greater abundance of wildlife found in the UK in the past and lower their expectations for how it can be restored.
Just under a third (31%) of butterfly species assessed in the UK show long-term declines, the monitoring scheme shows.
Dr Richard Fox, associate director of recording and monitoring at Butterfly Conservation, one of the organisations behind the scheme, warned that perceptions and measurements of what makes a good year have deteriorated over the decades.
“There are just fewer and fewer butterflies out there. There are some species doing well and bucking the trend, but in general there are far fewer butterflies out there,” he said.
“If we think that achieving the number of butterflies in our garden, on our farm, in our local county or across the UK as a whole, that 2020 is a great level to be at, then we are deluding ourselves, and forgetting what’s been lost.”
Long-term declines are mainly driven by human activity, particularly the loss of habitat and climate change, though on a year-to-year basis butterfly numbers are affected by the weather.
In 2020 the most significant weather impact on the winged insects was the very warm, sunny spring, which was “not only wonderful to help us all get through that first lockdown, it was fantastic for butterflies”, Dr Fox said.
Among common species, brimstone, orange-tip and marbled white all did well, although their numbers were not at the exceptional levels seen the previous year.
The small tortoiseshell’s numbers were up 103% on 2019 after a run of four bad years, but they were still below long-term averages and have seen a 76% decline since 1976, the study found.
The small pearl-bordered fritillary had its third worst year on record in 2020, and populations have declined by 68% since 1976, while wall, grayling and small skipper butterflies all remained at a low ebb, the experts said.
Populations of many rarer species of butterfly have benefited from conservation action by wildlife groups and landowners, and scarce species such as the large blue, silver-spotted skipper and Duke of Burgundy had some of their best years in the survey.
But populations of many widespread and common species are down since the survey began in 1976 and were almost certainly declining before that, so even a good year results in lower numbers than in the past, Dr Fox said.
He said everyone can do their bit to turn around the declines of common butterflies.
“What we really need is more wild areas, a bit of wildness in your garden, a bit of wildness in the local park or cemetery, a bit of wildness around farm fields.
“That done on a huge scale can only help – it provides breeding habitats, and this is what butterflies need,” he said, adding that it could be as simple as allowing grass to get long or leaving a patch of nettles to grow.
The UKBMS is led by Butterfly Conservation, the UK Centre for Ecology and Hydrology, British Trust for Ornithology, and Joint Nature Conservation Committee.