The pearl-bordered fritillary is a medium-sized butterfly with a wingspan of about 40 mm. Like many other fritillaries, the upper wing surface has black markings on an orange background. Underneath the hindwing there are two silver spots and, on the outer border, seven silvery 'pearl' markings. The adults are on the wing in May/June. There are several similarities in the lifecycle of this species and of that of the high brown fritillary, a species that is also covered by a SAP in this Plan:
One important difference is that the high brown fritillary overwinters as an egg and caterpillars first emerge in the spring. The caterpillars of the pearl-bordered fritillary emerge first in autumn, overwinter in this stage and then re-emerge in the spring.
The similarities mean that the pearl-bordered and high brown fritillaries share many of the same habitats and they are found at many of the same sites. For these reasons, the two species tend to be affected by the same environmental factors. Most of the sections in this Species Action Plan (SAP) are identical, therefore with their counterparts in the high brown fritillary SAP.
Main Habitat(s): Open deciduous woodland; scrub or coppiced woodland on limestone outcrops; well-drained grassland with either scattered scrub or abundant bracken.
The species has declined very rapidly during the present century, most notably in woodland in the last 50 years, and is now extinct in large parts of its former range. Current rates of loss stand at c.40% per decade in places (1).
The species is nationally scarce in Britain and is listed as a UK BAP Priority Species. It is included on Schedule 5 of the Wildlife and Countryside Act 1981 (for sale only).
In North West England the species occurs in suitable habitat in the limestone hills of the Morecambe Bay region, and in adjacent bracken rich habitats in North Lancashire and South Cumbria. Generally, these populations are regarded as stable (2).
Important sites in Lancashire are Gait Barrows NNR, Silverdale; Eaves Wood, Silverdale; Yealand Hall Allotments, Yealand Storrs; Warton Crag LWT/LCC/RSPB sites; Carnforth. Smaller populations occur at Silverdale Golf Course, Jack Scout, Three Brothers Allotment, and Heald Brow.
Current factors affecting the species
The continued careful management of habitat to benefit the species is crucial to its survival in the county.
In the butterfly's bracken habitats, for example, it is vital that bracken beds contain a dead litter layer that is not so dense that it prevents violet growth in the spring, but dense enough to suppress grass growth. This may be compromised by cessation of grazing or by inappropriate grazing regimes.
Winter and spring grazing by cattle is essential to prevent bracken stands becoming too dense and shading-out or smothering violet growth. Some light summer grazing may be beneficial as well. Trampling of actively growing bracken fronds can help to reduce the densiy of the bracken bed canopy, making it more favorable to violets and other ground flora. The replacement of heavier stock (cattle) with lighter animals (sheep) may result in development of over-dense stands and loss of violets.
In woodland on limestone, the species is dependent on the continuation of regular management by coppicing. Yet, even where coppicing is practised, a lack of deer management (by appropriate population control and exclusion measures) can threaten the long-term viability of coppice management.
Wide rides with sunny glades linking coppice plots are needed to provide breeding, feeding, and movement opportunities within sites. The cessation of such types of habitat management, particularly in small or isolated sites may cause individual populations to fail.
In an ideal situation, there should be a widespread network of several coppice rotations over an area to allow interaction between different breeding colonies and promote genetic diversity.
Current Action / Mechanisms
Within its range in north Lancashire, the pearl-bordered fritillary's preferred habitats of bracken, and coppice woodland on limestone are being actively managed by several agencies and organisations, including English Nature, RSPB, Wildlife Trust, Lancaster City Council and National Trust. Much of this habitat is on nature reserves, but several sites remain in commercial agriculture and forestry.
English Nature, the Farming and Rural Conservation Agency and Forestry Commission are developing and applying a protocol for advising landowners/managers of non-nature reserve sites.
A High Brown Fritillary Action Group (HBFAG) has existed since 1989. It is a partnership of statutory agencies, conservation groups, landowners and other key sectoral interests. In addition to working towards the conservation of the high brown fritillary, the HBFAG addresses the pearl-bordered fritillary as well
HBFAG co-ordinates annual monitoring of most known breeding sites. (Gait Barrows NNR; Yealand Hall Allotment; Eaves Wood; Warton Crag). This data is supplied to Butterfly Conservation nationally to contribute to monitoring progress with the UK SAP for this species.
A leaflet ‘Bracken for Butterflies’ was produced in 1997 by Butterfly Conservation and English Nature (3), outlining action for positive bracken management, and is available free to all.
Objectives, targets and proposed actions for pearl-bordered fritillary in Lancashire
References & additional reading:
1. HMSO (1995) Biodiversity: The UK Steering Group Report. Volume 2: Action Plans. Pearl-Bordered Fritillary SAP p.126.
2. Ellis, S. & Bourn, N. (2000) Butterfly Conservation Regional Action Plan North West England. Butterfly Conservation, Wareham, Dorset.
3. Joy, J. (1998) Bracken for butterflies. A leaflet published by West Midlands Branch of Butterfly Conservation.
Date: April 2001