Tough times for butterflies

This summer’s appalling weather, with its low temperatures, heavy rainfall and strong winds, may well be causing problems for many of our butterflies. Temperature can influence the time that it takes for a butterfly larva or pupa to develop, or reduce the activity of adults that need to find a mate or lay eggs. Of course, there is still much of the summer to go and we might find that as the weather picks up so do our butterflies.

The impression that you get of just how well a particular species is doing is very much shaped by where you live, which habitats you visit and when. Just because I have not seen many butterflies on the wing during my visits to local sites does not necessarily mean they are doing badly everyway. This is why we need the efforts of scientists, operating monitoring schemes in association with ‘citizen scientists.’ The changing fortunes of our butterflies, for example, are monitored through schemes like the BTO Garden BirdWatch (which records garden butterflies on a weekly bases throughout the year) and Butterfly Conservation’s annual Big Butterfly Count (www.bigbutterflycount.org).

Last year over 30,000 people took part in the Big Butterfly Count, which runs from 14 July – 5 August, and it would be great to see even more people involved this year. The survey is simple – a 15 minute count of the butterflies seen in a sunny place – and provides information on the more familiar and widespread species. For those species of a more restricted distribution, perhaps because they have more specialised habitat requirements, or which are more difficult to identify, there are other schemes. These typically involve fewer people and use more complex methods but they provide robust and essential results, generating a long-term measure of the changing fortunes of our butterfly species.

By recording butterflies in the same way from one week to the next, or from one year to another, provides a standardised measure of change, something that allows objective conclusions to be drawn about how particular species are doing. Some of the changes revealed may be the result of natural processes, perhaps a run of poor weather or an abundance of butterfly predators or parasites, while others may be the result of habitat or climate change driven by our activities.

In order to establish the effectiveness of conservation efforts we need to be able to say with confidence whether or not a species is responding favourable and the way to do this is by systematic monitoring. This is why the work of organisations like Butterfly Conservation and the BTO is so important. Since both organisations represent a partnership with volunteer surveyors, it is easy to see the valuable roles that you and I, as individuals, can play.

Something of a mixed year for butterflies

The results generated by the various recording schemes for butterflies have started to appear over the last few weeks. Looking across these it is possible to establish an idea of how 2010 shaped up and it seems that many species benefited from the hot June and July weather, which followed on from a cold winter.

As I noted in one of last summer’s columns, the summer heat helped species like White Admiral, which were able to shorten the time spent as a mature caterpillar and chrysalis and so reduce the levels of predation, a key factor to determining the size of the summer generation. Other butterflies, notably some of our less common species, also did well, with the Silver-washed Fritillary delivering the big success story for East Anglia. It appeared across the region in good numbers, re-establishing itself at some sites after a long gap.

Many of our familiar species did less well, especially immigrants like Red Admiral and Painted Lady, numbers of which were both very much down on the 2009 influx that grabbed the headlines. Such short-term fluctuations are not cause for concern. Some species exhibit regular changes in abundance that are shaped by parasite populations. The Holly Blue, for example, has populations that cycle depending on how common a particular small parasitic wasp happens to be. When the Holly Blue enjoys a good year, this allows the parasite to do well, meaning that the levels of parasitism will be greater the following year; this, in turn, brings the Holly Blue population back down.

Being able to see longer-term trends is a key component for any attempts to conserve our butterfly populations. This is where systematic recording schemes, like the Wider Countryside Butterfly Survey, carried out by volunteers from Butterfly Conservation and the BTO (many of the BTO’s bird recorders revisit their survey squares to record butterflies for this survey). Less common species are monitored by coordinated counts at key sites, as is the case with the Silver-studded Blue monitoring that takes place on some of the Norfolk heaths. Volunteers provide a key role in this work, working in collaboration with researchers to keep tabs on these changing populations.

Most butterflies are fairly straightforward to identify, meaning that (with a little training) you can make a valuable contribution to the work of organisations like Butterfly Conservation. If you would like to get involved in some of the butterfly recording work taking place across the county, or simply want to find out more about Norfolk’s butterflies, then why not contact the Norfolk branch of Butterfly Conservation. Visit www.norfolk-butterflies.org.uk or contact Chris Dawson on 01603 545092 if you would be interested in helping with their Wider Countryside Butterfly Survey.

Charity champions declining butterflies

This week has been designated ‘Save our Butterflies Week’ by Butterfly Conservation, a charity dedicated to the conservation of our various Lepidoptera (as butterflies and moths are known collectively). The week follows a new report into the changing fortunes of our butterflies, also published by Butterfly Conservation. The report, “The state of butterflies in Britain and Ireland” makes worrying reading, such has been the magnitude of decline for many formerly widespread species.  Norfolk itself has lost a quarter of its resident butterflies. Included among these are the large copper (which became extinct in 1864), small blue (1890s), chalk-hill blue (1971) and marsh fritillary (1970s). That we have lost so many species is a reflection of the changing land management and the loss of important habitats. The large copper, for example, was dependent upon areas of open fen, with high densities of the larval foodplant water dock, and as these disappeared so did the butterfly. Other species, like the high brown fritillary and the purple emperor have been lost as woodland habitats succumbed to modern management techniques.

For other species there is better news contained within the Butterfly Conservation report. The efforts of researchers, conservationists and volunteer lepidopterists have helped to secure the future of a number of species. The Norfolk Branch of Butterfly Conservation has been working hard to assess the habitat requirements of the silver-studded blue, a rare species, with a cluster of small colonies centred on the mid-Norfolk heaths. This delightful butterfly flies from June through into August and efforts have been made to see the number of colonies increase. The work, funded through the Heritage Lottery Fund has enabled the Norfolk Branch to hold training days, enabling volunteers to identify and monitor populations of this butterfly. The grant also funded a detailed study of all current and potential sites for the species within the county, with data collected on the condition of the heathland vegetation and on the densities of local ant populations (like a number of other blue butterflies, the silver-studded blue has a symbiotic relationship with one or more species of ant).

The result of all this work is a management plan for the species within Norfolk. The plan has established the size of the current silver-studded blue population and where it occurs. It has also highlighted sites where it is hoped that the butterfly can be established by moving a small number of individuals from existing sites with healthy populations. With luck, and quite a bit of effort, the future of the silver-studded blue should be secure. Now all we need to do is work on some of the other species that have declined over the years.

Common Moths undergo pronounced decline

It is about this time of year that I first put out my moth trap; a powerful light positioned above a collecting box. This enables me to record the many different species of moths that are nocturnal visitors to my garden, which would otherwise go unnoticed. The special mv bulb emits a light that is particularly attractive to moths, and those that collide with the bulb drop into the box below, ready to be identified and released the next morning. At the height of summer, following a warm, dark night, there may be dozens of moths in the trap.

Moth trapping is more than just an increasingly popular hobby, because the information collected can tell us about changes in the distribution and abundance of many of the 2,500 moth species to be found in Britain. Systematic recording using moth traps is at the centre of a new study published by Butterfly Conservation and Rothamsted Research. The Rothamsted network of light traps has been operating since 1968, collecting information from an average of 83 traps per year at sites across a range of habitats, from gardens and woodland through to moorland and coastal sites. An analysis of the trapping records, funded by the Esmée Fairbairn Foundation, has highlighted some staggering changes to the populations of many of our ‘common’ moths. The study charted what happened to 337 moth species over the period 1968 to 2002 and showed that two-thirds of the species had undergone a decline. The populations of 75 species had declined by over 70%, with an additional 57 species showing declines of over 50% and 60 species showing declines of over 25%.

Perhaps the most alarming thing about these findings is that virtually none of the declining species was previously thought to warrant any conservation action – these are species regarded by many as being ‘common and widespread’. Some of the biggest declines have hit familiar garden species, like Heart and Dart, Garden Carpet, Scalloped Oak and Common Wainscot. Since those species that use gardens tend to be generalists, the fact that they, too, are in decline should be sounding alarm bells. The reasons for such a general decline across species are likely to lay with habitat loss and a decline in habitat quality, with increasing pesticide use, light pollution and global climate change also playing a part.

Although the study did reveal an increase in a small number of moths, these were typically introduced species or those expanding their range northwards from the Continent. The results reinforce what many of us have noted over the years, a general reduction in the number of moths seen in car headlights while driving about at night and smaller catches in our traps.