RESEARCHING THE DECLINE
OF TWO ONCE-COMMON BUTTERFLIES

Small Heath

The Small Heath occurs in a wide variety of agriculturally unimproved grassland habitats. Recent analysis of butterfly transect data, collated by Butterfly Conservation, has highlighted an alarming population decline at monitored sites of more than 60% over the last 25 years (1976-2000). In Suffolk, large heathland sites such as Cavenham Heath NNR still support strong populations, but smaller sites within agricultural areas seem to be losing their colonies. As a consequence, a series of research projects has been established to identify the species conservation and management requirements and to identify factors influencing population trends.

In 2003, Gideon King of University College London carried out research into the species ecology and habitat requirements in lowland calcareous grassland.  Transect studies revealed that the highest densities of adults were located in short and species-rich grassland (NVC vegetation community CG2) with a relatively high cover of fine-leaved grass litter, herbs and nectar sources. The butterfly was found to be a generalist in terms of perches, and nectar sources used, but was quite fussy in terms of where it laid eggs.

Egg-laying requirements

The majority of eggs were laid:

In clumps of Sheep’s Fescue, in sheltered positions, in areas with an uneven topography
On dead brown leaf blades (litter) of Sheep’s Fescue, which provide a warmer microclimate
In short vegetation (two thirds eggs were in swards 4-5cm high)
Above soils with a uniformly low fertility.

Comparative analysis of trends in the butterfly at agri-environment scheme/non-scheme sites and SSSIs/non SSSIs, indicated that the butterfly has fared better at SSSIs than sites in agri-environment schemes. This may possibly be a reflection of (1) the more consistent management culture at downland SSSIs, which are managed chiefly for their short-turf botanical communities preferred by the butterfly, or (2) the greater variation in soil fertility at agri-environment scheme sites (including downland sites recently restored from arable land).

Management implications from the research

The butterfly requires a short (preferably herb-rich) sward though heavy summer grazing may be detrimental by removing grass litter required for breeding.

Research data suggests that the butterfly requires downland sites with an uneven terrain (created by stock poaching or naturally by erosion on slopes with a steep gradient).

Winter grazing by cattle or cattle and sheep mixtures, is likely to be a beneficial management regime for this butterfly.

Low soil fertility may be a requirement when creating and managing grassland habitat for the benefit of this butterfly.

Two further MSc research projects on the Small Heath have been established in 2004. Fieldwork is being conducted to identify thespecies requirements (especially egg-laying preferences) in two important (but previously unstudied) habitats: acid grassland and heathland. Neutral meadows and post-industrial grasslands are being studied separately. Investigation of weather associations is also to be investigated as the Small Heath thankfully fared much better at monitored sites in 2003, with favourable weather likely playing an important part in the recovery.

Wall Brown

Butterfly Conservation transect and distribution data highlight a rapid and worrying trend in the status of the Wall Brown butterfly, making it the fastest declining species of the general countryside. The geographic range of this once common, short-grassland butterfly has shifted southwards and it has declined dramatically or even disappeared from many inland sites resulting in a now largely coastal distribution. Over the last 25 years it has declined by over 70% nationally, raising it above the 50% threshold for UK BAP priority status. In Suffolk, its distribution is polarising; it is still found locally around Mildenhall, and is reasonably widespread within about 15 miles of the coast, but sightings in the rest of the county are now few and far between.

There is an urgent need to understand what is happening to this species and to establish methods to arrest its decline and enhance its status. Rebecca Harker (PhD student) and Dr Tim Shreeve from Oxford Brookes University will be researching between 2004 and 2006  the precise ecological requirements of the Wall Brown. The project will utilise butterfly transect data to research weather and management effects on trends in abundance.  The overall aim of this research is to make scientifically based recommendations for the management of sites in order to prevent further declines of the Wall Brown. 

Agri-environment scheme implications

As this is a wider countryside butterfly species, it is hoped the research will provide information which can feed into future refinements of the new Environmental Stewardship Entry Level Scheme (see below).

Changes to agri-environment schemes and future monitoring

In 2005, there will be substantial reform of agri-environment schemes in England.  Environmental Stewardship (ES) will be launched in 2005 to replace existing schemes.  CSS and ESAs will be merged to form part of Higher Level Environmental Stewardship (HLES), whilst more basic environmental improvements will be carried out through a new Entry Level Scheme (ELS). Organic Entry Level Stewardship will form the scheme’s third element.  Butterfly Conservation has made a substantial contribution to the design of the new scheme, to ensure that measures to help land managers conserve butterflies are fully incorporated.  The structure of ES, with many new positive elements and the emphasis on ‘outcomes’ rather than ‘management by rules’, has huge potential to improve the fortunes of butterflies and moths. Consequently, monitoring the impacts, in these exciting times, will be more important than ever. 

Butterfly Conservation and CEH have submitted an ambitious proposal to Defra to develop butterflies as governmental biodiversity indicators and to co-ordinate an integrated UK-wide scheme to monitor butterfly abundance. The proposals include  (1) merging CEH and BC transect datasets, and expanding the network of transects on special sites (where HLES will be  targeted) and (2) the development of a new monitoring scheme (using scientific sampling) for common species in the wider countryside (land open to the ELS).  Because butterflies are such sensitive biodiversity indicators, this new integrated butterfly monitoring scheme would undoubtedly play a key role in assessing the effectiveness of ES in conserving biodiversity.

Rob Parker, Chairman of the Suffolk Branch of Butterfly Conservation
66 Cornfield Road, Bury St Edmunds, IP33 3BN

© 2004   Suffolk Naturalists' Society

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