2020 was a ‘good’ year for butterflies in the UK

The results from the annual UK Butterfly Monitoring Scheme show that last year was a 'good' year for butterflies, but conservationists warn of the dangers of shifting baseline syndrome.

Duke of Burgundy. © Iain H Leach/Butterfly Conservation

2020 was a ‘good’ year for a number of butterfly species, including a number of common species and some that are targets of conservation action such as the large blue, silver-spotted skipper, silver-studded blue and Duke of Burgundy.

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“Despite 2020 being a challenging year for data gathering and conservation activity, we received nearly half a million records from more than 2,500 sites over the year,” says Dr Marc Botham, butterfly ecologist at the UK Centre for Ecology & Hydrology (UKCEH).

“We are incredibly grateful to the thousands of volunteers who were able to carry out COVID-safe monitoring and maintain this invaluable long-term dataset. Thanks to volunteers’ efforts and advances in analytical methods, we were able to report on population levels on all but one of our UK butterfly species in 2020.”

The UK Butterfly and Monitoring Scheme (UKBMS) has been running sing 1976, providing long-term data for conservationists to compare recent data to. The sightings come from weekly counts along defined transects between April and September, with additional sightings fed in from the Wider Countryside Butterfly Survey and from targeted species surveys.

The scheme is run by Butterfly ConservationUKCEH, British Trust for Ornithology (BTO) and Joint Nature Conservation Committee (JNCC).

Brimstone. © Iain H Leach/Butterfly Conservation
Brimstone. © Iain H Leach/Butterfly Conservation

Widespread species that also enjoyed a ‘good’ year include brimstone, orange-tip, and marbled white. Small tortoiseshell also had a relatively decent year after four years of low numbers, but still shows a decline of 79% in abundance since 1976.

Although 2020 was the third good year in a row for the UK’s butterflies, the long-term data shows that almost half of the species were recorded at below average numbers.

The small pearl-bordered fritillary experienced its third worst year on record, having declined by 68% since 1976.

Small pearl-bordered fritillary. © Andrew Cooper/Butterfly Conservation
Small pearl-bordered fritillary. © Andrew Cooper/Butterfly Conservation

“Perhaps because of the warm sunny spring weather last year and the fact that more people were enjoying nature as part of their day-to-day activities than ever before, butterflies seemed more numerous,” says Dr Richard Fox, Butterfly Conservation’s associate director of recording and monitoring. “But in fact, our baseline experience of the nature around us has changed over time.”

“It is worrying that, even after three good years, population levels of so many butterfly species continue to be down compared to 40 years ago, with just under a third (31%) of butterfly species assessed in the UK showing long-term declines.”

“We need to be wary of shifting baseline syndrome, whereby we forget (or never experienced) the greater biodiversity that occurred in the UK in former decades and therefore lower our expectations and aspirations for conservation. Here the UKBMS has a vital role to play in showing how insect populations have declined over time.”

Largest long-term decreases and increases in abundance of UK butterflies

Species: Long-term UK trend (Date period)

  • Heath fritillary: -91% (1981-2020)
  • Wall: -87% (1976-2020)
  • Wood white: -83% (1979-2020)
  • Small tortoiseshell: -79% (1976-2020)
  • White-letter hairstreak: -78% (1976-2020)
  • Lulworth skipper: -76% (1992-2020)
  • Small skipper: -71% (1976-2020)
  • Grayling: -71% (1976-2020)
  • Small pearl-bordered fritillary: -68% (1976-2020)
  • Pearl-bordered fritillary: -66% (1976-2020)

Species: Long-term UK trend (Date period)

  • Large blue: 2191% (1983-2020)
  • Clouded yellow: 649% (1979-2020)
  • Silver-spotted skipper: 640% (1979-2020)
  • Large heath: 443% (1990-2020)
  • Black hairstreak: 435% (1995-2020)
  • Ringlet: 364% (1976-2020)
  • Silver-washed fritillary: 257% (1976-2020)
  • Red admiral: 254% (1976-2020)
  • Dark green fritillary: 246% (1976-2020)
  • Comma: 197% (1976-2020)

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Main image: Duke of Burgundy. © Iain H Leach/Butterfly Conservation