Original article by Richard Fox, Surveys Manager, Butterfly Conservation. Read about the way in which Britain’s butterflies are responding to changes in our climate, and how they may continue to teach us about the changes that are occurring.
Butterflies are excellent indicators of the effects of climate change on the wildlife of Britain. Not only do they respond rapidly to subtle shifts in temperature, but there is also long history of butterfly recording in Britain. As a result, we have a huge amount of information about the distribution of each species over the past 200 years, and can use this to measure recent and future change.
The White Admiral is an expanding species. Photo:Alan Barnes
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Butterflies as indicators of climate change
Butterflies and climate are inexorably linked. Most of our butterfly species reach a clear limit to their European range in Britain and, for the majority, this limit is due to climate rather than the availability of habitats or the plants upon which their caterpillars feed. Such species should spread into new areas (typically further north) if the climate becomes warmer. The spread can be measured simply by recording where butterflies occur now in comparison to historical distributions.
National Butterfly Survey
In 1995 The Butterfly Conservation and the Biological Records Centre launched a new national survey to determine how butterflies are faring in the face of climate change and habitat destruction. The Butterflies for the New Millennium project, as the survey was known, soon became the largest and most comprehensive survey of butterflies ever undertaken in the British Isles. In the first five years, 10,000 members of the public submitted over 1.6 million butterfly sightings covering virtually the whole of Britain and Ireland.
The pattern of change
The Butterflies for the New Millennium data show that the distributions of almost all our 59 species of butterfly have changed substantially in the past 200 years. Some of these changes have been gradual, but others have occurred more rapidly, especially during the last 50 years. More than half the species have declined substantially since 1800, including five that have become extinct and 15 that have been lost from more than 50% of their previous distribution. The main cause of decline is the wholesale and ongoing destruction of wildlife habitats for intensive agriculture, forestry and urban development. The survey found that losses had continued and, in some cases, accelerated in recent decades and that 4 species had declined by over 50% since the last survey in the 1970s.
The Peacock's fortunes are reviving. Photograph by Jim Asher.
Some butterflies respond to the warming climate
Even though the extent of most butterfly habitats has declined, a key finding of the Butterflies for the New Millennium survey is that 15 species have spread substantially since the 1970s. Climate change is almost certainly the cause. Two species, the Essex Skipper and Brown Argus have more than doubled their British distribution in the past 20 years. In addition, the Holly Blue, Comma, Purple Hairstreak, Marbled White, Speckled Wood and Ringlet have all expanded by more than 50%. Other climate-related changes are evident too. Butterflies are appearing earlier in the year and some species are managing to fit in an extra generation during the summer.
The Essex Skipper is spreading away from current core areas. Photograph by Alan Barnes.
Most of the expanding butterflies are spreading northwards in Britain, although the pattern of change varies with each species. Some have spread away from core areas that have been occupied for many decades (e.g. Essex Skipper and Brown Argus). Others, including the Orange-tip, White Admiral, Peacock, Comma and Speckled Wood have re-expanded following an earlier contraction during the late nineteenth and early twentieth century.
These recent expansions have been mirrored by range shifts elsewhere in Europe. Other insects have been on the move too. Moths such as Small Ranunculus and Bloxworth Snout appear to have colonised Britain in recent years and rapid expansions have been recorded recently amongst crickets (e.g. the Roesel's Bush-cricket and Long-winged Cone-head) and dragonflies (e.g. the Migrant Hawker, Emperor and Ruddy Darter).
Life in a changing climate
The Butterflies for the New Millennium survey has shown that many common butterflies have extended their distributions in response to the changing climate. However, despite this background of favourable climatic conditions, many specialist butterflies continue to decline. Further analysis shows that the majority of butterflies with expanding ranges can be classified as wider countryside species - mobile, generalist species that are widespread and common in the countryside. So why have only wider countryside species been able to profit from climate change favourable to them? The answer lies in the structure of the modern landscape. Mobile common species are able to move through the landscape, usually finding some breeding habitat (e.g. hedgerows, patches of nettles or long grass) even in intensively farmed or urban areas. Therefore, they have been able to track the shifting patterns of climate.
In contrast, the habitats used by rarer butterflies have been much reduced by human activity. Many remaining patches of, for example, chalk downs, lowland heath and ancient woodland are simply too small and isolated to be colonised, even if they become climatically suitable. More worryingly, the habitat patches already occupied by these butterflies may become inhospitable as the climate changes. For example, the south-facing downland slopes currently favoured by warmth-loving species such as the Silver-spotted Skipper and Adonis Blue may become too hot or drought-prone.
Susceptible to climate change: the Adonis Blue. Photograph by Ken Willmott
Similarly, mountain ringlet, our only butterfly adapted to live in high mountains, may find its habitat increasingly squeezed as climatic zones shift to higher altitude. Because of these threats, conservationists are recognising the need for a landscape-scale approach, which focuses on the conservation and extension of existing nature reserves and all remaining patches of habitat, so that species are able to move in response to the changing climate.
More information needed
Although we know that many butterflies are being affected by climate change, the impact on each species is difficult to predict. this is because the responses will depend on a complex interaction between the plants and animals, and the environmental conditions that shape their habitats. there are also uncertainties about how the climate will change. average annual changes in temperature and rainfall across regions are of limited value for predicting the responses of wildlife, which are affected by fine-scale climatic changes. in the short-term, measuring the distribution responses of good indicators, such as butterflies, may be the only practical means of assessing the impact of climate change on the many thousands of other species that make up our wildlife.
Silver spotted skipper at risk from hotter weather. Photograph by Alan Barnes.
How you can help
In order to assess the impact of future climate change it will be vital to continue recording butterflies and other wildlife. anyone can help with this. You can do as much or as little as you like and you certainly don't have to be a butterfly expert. For more information on butterfly recording, please contact Butterfly Conservation, Manor yard, East lulworth, Wareham, Dorset BH20 5QP (tel: 01929 400209) or look at our web site (see link in ‘where next?')
All of the findings of the butterflies for the New Millennium survey have been published in a colourful new book The Millennium Atlas of Butterflies in Britain and Ireland (ISBN 0 19 850565 5), published by Oxford University Press.
In this section, see the articles ‘Challenge for conservation' by Dr Pam Berry from the Environmental Change Institute for some of the background to the challenge that climate change is posing to biodiversity and conservationists, and ‘Swallows linger longer', describing a programme involving the british public in recording ‘phenology'- the observation of timings of natural phenomena.
Visit the butterfly conservation website for information on events, activities and resources to protect butterflies.
The biological records centre is the national custodian of data on the distribution of wildlife in the british isles. this is the site for you if you are a naturalist with observations to report, or are looking for information on biological recording activities, or need to use some data.
The butterflies for the new millennium project website gives details of the activities described in this article.