Half of British butterfly species are now threatened with extinction after five more joined the new “red list” of endangered butterflies.
The increase in the number of species listed as “vulnerable” again in 2011 to 16 today is a warning that time is running out to save the 58 resident species, according to Butterfly Conservation, which compiled the red list from of scientific monitoring data according to the criteria established by the International Union for Conservation of Nature (IUCN).
But there are positive trends on the list, which covers 2010-19 data, with two of the most endangered species, the great blue and the great brown fritillary, coming out of the highest risk category after a specific conservation.
The Great Blue, which became extinct in 1979 but was reintroduced from Sweden, has gone from “critically endangered” to “almost threatened”, the least risky of IUCN’s endangered assessments apart from the “lesser concern.” It thrives in restored wildflower prairies in the Cotswolds and Somerset.
In recent years, the tall brown fritillary has been seen as the species most likely to become extinct from the great blue.
But conservation efforts in the south-west of England and its only remaining site in Wales have been successful. The butterfly has recovered, although its distribution among the sites continues to decline, meaning it is now “vulnerable” rather than “critically endangered”.
“Given that the overall picture is a growing risk, the fact that the highly endangered species that have been the focus of the conservation effort has been less threatened is a real plus,” said Richard Fox of Butterfly Conservation. “With significant effort and resources we can at least maintain these species and, in some cases, reverse them.”
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Other success stories include the Duke of Burgundy and the pearl-trimmed fritillary, which went from “endangered” to “vulnerable” following a conservation action led by charities and local communities.
But there is a growing concern for other species that were once thriving that have moved into the “vulnerable” category. The blue Adonis pattern, blue and silver Chalkhill have been moved despite decades of conservation work to increase their numbers.
All three species require warm, short, flower-rich gypsum pastures, all of which declined disastrously in the mid-20th century with the loss of these pastures and a reduction in traditional grazing.
Since the 1980s, all three have revived and appeared to benefit from global warming, moving north to new locations. However, its decline in the last decade may be caused by new factors, such as increased nitrogen deposition, agricultural fertilizers and vehicle pollution, which lead to vigorous weeds that drive out wildflowers more delicate that butterfly caterpillars need to survive.
“It’s disappointing to see these species return to the endangered group,” Fox said. “Insidious changes in the environment due to climate change or nitrogen or both mean that the habitat created by conservation management 20 years ago does not necessarily produce the same results today.
“Land managers have to keep experimenting to produce suitable habitats for species like these because everything else is changing. In the Netherlands, scientists are convinced that nitrogen deposition is a major factor in the decline of some of their rare butterflies “.
The negative impact of global warming is evident in the inclusion in the endangered categories of the four butterflies found in colder, northern habitats. The large heather, the Scottish argus and the northern brown argus are now listed as “threatened” and the mountain ash is “almost threatened”. ”. The four species are likely to disappear from the southern parts of their distribution.
The red list requires five years of positive data before an endangered species can be considered resurrected, so the new list does not yet reveal improvements.
These include a resurgence of white wood after intensive conservation management. While another butterfly, the large turtle, listed as extinct, has mysteriously reappeared in various places in the south of England as a breeding butterfly since 2019.