An afternoon of learning about the impact of climate change on our butterfly population, and how we can help mitigate against future loss through habitat management efforts today.

By Nicola Ceconi ǀ Senior Ranger, Forest of Marston Vale

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Photo credit: Don Morris

At the end of April I joined entomologists and fellow butterfly enthusiasts around the country for a webinar titled 'Some Like it Hot: Butterflies in a Changing Climate' presented by Marcus Rhodes - an ecologist based at the University of Exeter - as part of the Field Studies Council’s “Natural History Live” program.

We looked at how climate change is affecting butterflies, which was very timely as I have recently set up and am now running the volunteer butterfly survey group across the Forests sites.

Through the course of the webinar we learnt about the importance of studying butterflies in relation to climate, because they:

• are cold blooded, so get their body heat from their surroundings and are sensitive to change
• have short life cycles - sometimes only having one generation a year - so changes in temperature can have a big impact on the population the following year
• are very well recorded. The UK Butterfly Monitoring Scheme has been going since 1976, so there is lots of data on population sizes.

Different butterfly species respond differently to climate change

Climate change winners

Comma and speckled wood butterflies have both spread north as a result of warmer temperatures.

Brown argus used to be confined to chalk grassland: locally this habitat is typical of the Chiltern Hills, which includes the Dunstable Downs. The brown argus has been able to vary its diet to include geranium, as well as its traditional staple diet of rock rose and is now found over a wider area.

Small blues are emerging earlier - they now have two generations a year, which is leading to increased numbers because they have more chance to reproduce.

Photo credit: Don Morris

Climate change losers 

Unfortunately for every success story there does appear to be a converse reaction elsewhere.

The mountain ringlet is now only found above 250 metres (820 feet) in the Lake District and Scottish Highlands, and numbers have dropped as they are being pushed higher up the mountains by the rise in temperature. The northern brown argus and scotch argus have also reduced in numbers as temperatures rise.

Like the small blues, the silver studded blues are also emerging earlier, but they have only one generation a year. Despite their earlier emergence their numbers have either been reduced or remain static. The earlier they emerge the less likely they are to find their food plant in flower.

The wall brown butterfly has disappeared from large parts of inland central England, and is now trying to fit in a third generation in its lifecycle, instead of overwintering as a caterpillar - these late produced caterpillars do not have time to get big enough to survive the winter, which is driving the decline.

Micro climates

Marcus Rhodes explained how normal air temperatures can vary considerably, depending upon vegetation and which direction slopes are facing. We looked at how laser imaging can map these micro climates, and how findings can be compared to what we know about how each species is responding to climate change and to predict how they are likely to be affected in the future.

We also learnt how different species regulate their body temperature to react to changes in climate in different ways. For example, white butterflies are reflective baskers: they tilt their wings up slightly and the heat reflects off them and is bounced down to their bodies. This helps them warm up quickly and means that they are often on the wing earlier than other butterflies - perhaps why these are spotted earlier in the day in our gardens and woodlands.

Photo credit: Don Morris

The future for butterflies in a changing climate

Although on the surface it appears that some butterfly species are benefitting from the changes, this is being offset by loss of habitat - three-quarters of our butterfly species are in decline. Better conservation management and increasing links between sites would help reduce this.

A greater understanding of micro climates can also help off-set negative effects on species that are being pushed further north and becoming extinct in southern areas, and the introduction of butterflies to new areas where they have not been able populate naturally would increase their range.

As we're now starting to record data from our Community Woodlands and Forest sites it will be interesting to see how many of the principles we looked at during the session will impact the information collected -  I look forward to seeing what comes in and keeping you all posted with updates!

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