Speckled Wood - Mark Radford.JPG
The World Meteorological Organisation has declared 2021 to be one of the seven warmest years on record, with the average global temperature about 1.11°C above the pre-industrial levels.
With the warmest seven years all coming since 2015, and 2016, 2019 and 2020 constituting the top three, there can be no denying that climate change is causing temperatures to rise. The question we are asking though, is how is this affecting our butterflies and moths?
Professor Jane K Hill (Hon Fellow of the Royal Entomological Society) is Professor of Ecology at the University of York. Her research interests include the effects of climate change and habitat degradation on insects.
Professor Hill recently wrote an article for Butterfly Conservation’s membership magazine Butterfly. She writes…..
Much of our understanding about the ecological consequences of global climate change comes from studies of butterflies in Britain. This may seem surprising, but information is needed on the fortunes of species over many years for us to understand the impacts of climate change. Such detailed long-term information is very rare globally, but Britain is unique in having data going back to the 1970s, and even earlier, when the fingerprint of human-caused climate change became increasingly evident.
The information comprises citizen-science observations, such as sightings uploaded to iRecord, which generate information on how distributions are changing. There is also information from fixed transect sites that are walked regularly for the UK BMS (Butterfly Monitoring Scheme) and provide information on how the numbers of individuals are changing. Butterfly populations vary considerably from one year to the next, irrespective of any global climate effects, and any long-term trends can only be detected from many decades of monitoring.
These two types of information tell us different things about the responses of butterflies to climate change, and together are very powerful for understanding how biodiversity may fare in future. The face that British butterflies are at the forefront of our understanding of climate change is because, compared with many other countries, Britain has relatively few butterflies (about 60 species) but a huge number of enthusiastic recorders, reflecting people’s fascination for the natural world since Victorian times, and their wish to conserve it.
What about the consequences of climate change?
Butterflies have responded to climate change in many different ways. Some species have benefitted, expanded their ranges and colonised new sites further north. The Comma, once confined to the south-west, is now breeding in Scotland, spreading its range northwards at a rate of about 10km a year.
Several others reach the northern limits of their European ranges in Britain, and many of these species have spread north. The Speckled Wood is spreading more slowly than the Comma and lagging behind climate changes because it relies on woodlands at its northern range edge, which are often patchy and hard to reach. However, montane and northern species have suffered, and climate warming is causing local extinctions where sites become too hot or dry.
The Mountain Ringlet has disappeared from over a third of sites, and extinction of local populations may also lead to the loss of unique genetic diversity.
In addition to distribution changes, some butterflies are responding by emerging earlier in spring, which has positive benefits for some species by increasing their numbers and expansion northwards. However, despite these successes, UKBMS data show that about half of British butterflies are undergoing long-term declines in abundance, and climate warming need to be considered alongside other human-caused factors, such as the loss of habitats, use of pesticides, and pollution.
What might the future hold?
For British butterflies that benefit, managed landscapes to improve connectivity will help them extend their ranges northwards and keep track of the climate changes. Migrant species such as the Painted Lady may become more common, especially if they become residents, and European species, such as the Map, may colonise Britain if they can cross the Channel.
We may see the return of species that long ago went extinct in Britain, such as Black-Veined White and Large Tortoiseshell. Successful re-introductions of Large Blue and other successes highlight that sites can be managed to boost numbers, and landscape-scale approaches help protect networks of sites.
The outlook is bleaker for populations of cool-loving montane species, such as Mountain Ringlet, threatened by climate change at their low elevation sites. Local site management may help slow their decline, but reducing global temperature rise is urgently needed. Meanwhile, more drastic measures may be required, such as translocating individuals (and their genes) to cool refuge locations, if they can’t get there themselves.
More monitoring is also vital, to ensure early warning of populations at risk, buying us time to implement effective conservation management and gain better understanding of how butterfly changes have knock-on effects more widely for food webs and ecological communities.
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