Wyre Forest Study Group

Transcription

1 Background to Project The Pearl-bordered Fritillary Boloria euphrosyne was once a widespread and abundant butterfly in England but has undergone a dramatic and accelerating decline over the past 100 years, such that it is extinct in most eastern and central counties. Within the West Midlands Butterfly Conservation region (i.e. the counties of Gloucestershire, Herefordshire, Shropshire, Staffordshire, Warwickshire, West Midlands and Worcestershire) the Pearl-bordered Fritillary retains strongholds in the Wyre Forest (on the Shropshire/Worcestershire border) and Cirencester Park woodlands (in Gloucestershire). It has responded well to recent management at Haugh Wood (Herefordshire) and survives at a few other scattered localities in the region (most notably in the Oswestry Uplands). However, over the past 10 years it has been lost from former strongholds, including the Forest of Dean, Malvern Hills and the Cotswolds away from Cirencester Park, and most single site localities, including Trench Wood. This was the last site for the Pearl-bordered Fritillary within the complex of woodlands in east Worcestershire which are relics of the ancient Feckenham Forest. The main habitat in which the Pearl-bordered Fritillary occurs (and occurred) in the West Midlands region is woodland clearings, although it is/was also associated with bracken, grass and scrub mosaics (e.g. in the Malverns). Occupied habitat patches are characterized by: PEARL-BORDERED FRITILLARY SURVEY 2002 being dry, sunny, sheltered and usually southfacing containing an abundance of common dogviolets (Viola riviniana) growing amongst a shallow (<15cm deep) layer of litter (bracken or leaves) The presence of spring woodland herbs for nectaring, especially bugle (Ajuga reptans) These conditions reflect the critical requirement for a warm microclimate to stimulate rapid larval development in the early spring. Historically, the Pearl-bordered Fritillary was widespread in coppiced woodlands. The abandonment of most large scale commercial coppicing saw many former sites becoming too shady to support the butterfly with a consequent loss of colonies, increasing isolation of surviving ones and a breakdown of metapopulation structures resulting in an accelerating pattern of local extinctions. The decline of the Pearl-bordered Fritillary has been so dramatic that of British butterflies possibly Jenny Joy only the High Brown Fritillary (Argynnis adippe) currently surpasses it as a focus for conservation concern. Nationally, the Pearl-bordered Fritillary is a priority species within the UK. Aims The main aim of this project was to determine the current status and distribution of the Pearl-bordered Fritillary within the Wyre Forest. It was anticipated that the results of this survey could then be used to: Assess whether the Wyre Forest population is strong enough to be used as a donor population for future re-establishments in the region (see Barker, 2002) Identify the future monitoring requirements of this species. As the flight period of the Pearl-bordered Fritillary coincides with that of the Argent & Sable and Drab Looper moths (both Biodiversity Action Plan (BAP) species - and both have been recorded in the Wyre Forest in the recent past), one additional aim of this project was to try to record these two moth species and to identify some of the characteristics of the areas where they are recorded within the Wyre Forest. One former stronghold of the Pearl-bordered Fritillary in east Worcestershire is Feckenham Forest which has been identified by Butterfly Conservation's West Midlands Region Conservation Committee as having a network of sites with the potential to re-establish this species. An additional part of this project (see Barker, 2002) was therefore to look at the feasibility of reestablishing this species in the Feckenham Forest. This appeared to be the first time that the possibility of re-establishing this species had been considered at the landscape rather than individual site level. The Wyre Forest and Forest of Feckenham projects addressed a number of the actions listed in the UK BAP Species Action Plan for the Pearl-bordered Fritillary (Biodiversity Steering Group Report, 1995). These actions are as follows: Where feasible, encourage restoration of suitable habitats throughout the butterfly's former range to aid restoration programs. Following feasibility assessments and habitat restoration, where necessary, seek to restore 35

2 populations to at least three sites per previously occupied county. Promote surveys to identify the locations of large and medium-sized colonies and to identify potential sites for re-introduction. Encourage regular monitoring of extant sites. This project also addressed a number of the actions listed in Butterfly Conservation's Species Action Plan for the Pearl-bordered Fritillary (Barnett & Warren, 1995). These actions are as follows: Maintain/restore coppicing and active broadleaved management throughout range (especially measures that will increase the frequency of large canopy gaps near existing populations). Encourage restoration of suitable breeding habitat within former range, where there is potential for re-establishing viable networks of populations. Conduct strategic re-introductions of Pearlbordered Fritillary into networks of suitably restored habitat. Identify location of all large/medium colonies. Identify potentially suitable, unoccupied habitats within km of existing populations. Identify potentially suitable, unoccupied habitats in former range greater than 20 km from existing populations. In addition, these projects also addressed several of the actions listed in Butterfly Conservation's West Midlands Regional Action Plan (Joy, 1997). These actions are as follows: Increase the level of monitoring to cover all surviving colonies by at least a spot check, a full species transect or a timed count. Seek to safeguard all existing colonies and take opportunities to extend suitable breeding areas within or adjacent to surviving colonies. Consider a programme of re-establishment to former sites as ecological knowledge, opportunity and resources allow, in line with the national species action plan drawn up by Butterfly Conservation. Methods The Study Area Large parts of the Wyre Forest are managed by Forest Enterprise (FE). The National Nature Reserve (NNR) is managed by English Nature (EN) and FE amongst others and other parts of the wood are in private ownership. The Worcestershire Wildlife Trust (WWT) also has a small reserve within the Forest (Knowles Coppice and Betts Reserve). The main block of forestry is around 2430 hectares with the Site of Special Scientific Interest (SSSI) covering some 1753 hectares and the NNR some 572 hectares. Due to its scale, this project involved considerable volunteer input as well as liaison with EN, FE and private landowners. Different areas of the forest were identified and volunteers given a section in which to target their recording effort. Recording sheets were handed out to try to ensure consistency in recording methods and to encourage identification of other factors in addition to the number of adults present. These factors included behaviour (e.g. feeding records, egg-laying or territorial behaviour), abundance of foodplants in the area where adults were seen and the type of habitat (e.g. meadow or area of clear-fell). If individual volunteers managed to cover their target areas, they were then encouraged to take on additional areas. The following land was initially targeted for survey: All land managed by FE All areas of the NNR (including land under private ownership). Land owned by private individuals Additional sites and areas around the periphery of the forest which were thought to possibly contain suitable habitat. Within these areas of the forest, priority was given to: Areas where Pearl-bordered Fritillary had been recorded in the past Areas which had recently been coppiced or clear-felled Areas which were found to support potentially suitable foodplants for the Argent & Sable and Drab Looper moths. Attempts were also made to ensure that all the timed counts carried out by Frank Lancaster and Michael Taylor in 1997, (as part of a national survey co-ordinated by Butterfly Conservation and targeted at the Pearl-bordered Fritillary), were repeated in order to identify any changes in the size of colonies at these locations. Additional timed counts were carried out at as many sites as was possible to give estimates of colony size in additional areas of the forest. Timed Counts In a certain number of butterfly species, e.g. the Heath Fritillary (Warren et al., 1984) and the Small Pearl-bordered Fritillary (Stewart et al., 2002), absolute population estimates have been worked out using mark-release-recapture (MRR) experiments. They are then compared with rough population estimates obtained from the same sites using timed counts. As the timed counts obtained during these research projects have been found to 36

3 be a good indicator of population size, they have recently been increasingly used by Butterfly Conservation to obtain a rough estimate of population size on sites where it is not practical to carry out lengthy MRR experiments. Timed counts are also a simple way of recording variations in abundance from year to year. They identify whether numbers are increasing or decreasing in response to management or other factors. A single visit is usually sufficient if this is made close to the predicted peak adult flight period. The number of butterflies seen during a systematic search of the flight area is recorded in a measured time period. If the count is not undertaken at the peak flight period it can be adjusted by comparing it to numbers recorded on the nearest butterfly transect (and multiplying it up accordingly). Timed count data is frequently converted to relative density by using the following formula: Relative Density = Number seen per hour x flight area (in hectares) The relative density can then be used to identify whether the colony is likely to be large (>1,000 adults), medium (100-1,000 adults) or small (<100 adults) following Butterfly Conservation's definition of colony size for Pearl-bordered Fritillary (Barnett & Warren, 1995). However, as many of the Wyre sites were only visited by one recorder in 2002, the identified flight areas and time spent undertaking timed counts were often very small. There was confusion as to which week was the peak flight period for the Pearl-bordered Fritillary in the Wyre Forest in It was felt that the conversion of timed count data to relative density estimates were not appropriate here and could have given erroneous results. For this reason, the categories of population size used by Matthew Oates in his study of the Pearl-bordered Fritillary in Cirencester Park Woods (which used similar methods to those used here, see Oates, in prep.) were adopted for this study and are as follows: Large = peak season counts of >50 Medium = Small = <21 Summary of Results A comparison of the 1997 and 2002 timed count data initially presented a depressing picture. At only one site does the Pearl-bordered Fritillary colony appear to have increased in size, at 9 sites they appear to be stable and at 24 sites they appear to have undergone decline. These results cannot be attributable to the weather as there was fine weather from mid March onwards in both years (suggesting comparable levels of adult emergence) and the timed counts were carried out under similar weather conditions. The majority of these sites (76%) currently only support small colonies, 24% support medium sized colonies with no sites continuing to support large colonies. Nevertheless, the 2002 survey has identified 9 additional sites and areas, which are now important for the Pearl-bordered Fritillary with singletons being recorded in four additional places. Colony size assessments suggests that six of these additional colonies were small and three were of medium size. Overall, the 2002 results suggest that the Wyre Forest still supports a healthy Pearl-bordered Fritillary population and therefore is currently strong enough to be used as a donor population for future re-establishments of this species in the West Midlands region. However, stock should only be taken in years when the level of emergence is likely to be high (i.e. when there is good weather from March onwards) and from sites or areas which are known to support strong colonies. Also, as work by Matthew Oates (Oates, in prep.) has shown that the status of the Pearl-bordered Fritillary can change very rapidly (in Cirencester Park Woods in Gloucestershire from 22 distinct colonies in 1997 to only 5 colonies in 2002), it is important that the status of this species in the Wyre Forest is continually reviewed so that it is only used as a donor population when it is appropriate. One feature that many of the additional Pearlbordered Fritillary sites identified in 2002 share is that they contain an extensive area of clear-fell or recently opened up area of land. As the extent of clear-fell planned for the FE section of the Wyre Forest in the future is much reduced, (due to the planned reversion of the forest to broad-leaved woodland), and the level of coppicing may also be lower here than originally envisaged, (due to slow coppice re-growth), the impact this will have on the Pearl-bordered Fritillary in the future needs consideration. Some possible ways forward may be: To increase the amount of land in the coppice cycle To see whether open space can be maintained as suitable breeding habitat by management such as rotational scarifying and cutting. Bugle was found to be the major nectar source utilized although adults were seen feeding on seven other plant species including tormentil and bird'sfoot trefoil. Egg laying behaviour was only observed at three sites with two eggs being located at one site. Interestingly, in 60% of cases where adults were found, violet abundance was recorded as rare (in contrast to 37% of cases where violet abundance was frequent or 3% of cases when they were abundant). This result may reflect the time of year the recording were made and the fact that it was difficult to look for butterflies and search for violets simultaneously. 37

4 Two transects continued to be recorded in the Wyre Forest during 2002 (Wyre Forest East and Wyre Forest West). While there is no doubt that it is important that these two transects continue, it is suggested that an additional ten sites be monitored annually by timed counts. The initial sites proposed are the IMI Compound, FE Pipeline, FE Longdon Orchard, FE clear-fell above the Experimental Pond, FE Wimperhill Deer Lawn and Wildlife Corridor, FE Railway Line, NNR Railway Line, NNR Withybed Wood, NNR Longdon Wood and one of the NNR coppice coupes. Ideally this list should be reviewed annually (with any unsuitable sites being removed and newly created areas of habitat included) so that it adapts to changing circumstances. Additional priority work for 2003 should ideally include: Violet assessment in April on all key Pearlbordered Fritillary sites (giving priority to medium colonies). Identification of Pearl-bordered Fritillary breeding areas and types of habitat involved (e.g. deer lawns, meadows and pipelines etc.). Expansion of the experimental management programme. Assessment of the use of scallops by Pearlbordered Fritillary. Further work on Pearlbordered Fritillary breeding sites (including violet assessment) in the Wyre Forest is particularly important as this information could be used to 'guide' future management as well as helping to determine whether the Forest of Feckenham area of Worcestershire is in a suitable condition for a re-establishment. It was disappointing to record no Argent and Sable or Drab Looper Moths as part of the 2002 survey. Nevertheless a number of other interesting moth species were recorded. These included Small Purple-barred (a species which is rare in Shropshire and in Worcestershire was last recorded in the Wyre in 1991), Marbled White-spot (the Wyre Forest being a well-known site for this uncommon species) and Schiffermuellerina grandis at Ribbesford Woods. This last species feeds on dead wood, is classified as a proposed Red Data Book (prdb) 1 species and is currently only known from Somerset and south Devon. References Barker, S The feasibility of re-establishing the Pearlbordered Fritillary Boloria euphrosyne in Feckenham Forest, East Worcestershire. Unpublished report to English Nature and Butterfly Conservation. Barnett L. K. & Warren, M. S Species Action Plan Pearlbordered Fritillary Boloria euphrosyne. Butterfly Conservation, Wareham. Biodiversity: The UK Steering Group Report Volume 2: Action Plans. HMSO, London. Joy, J West Midlands Regional Action Plan. Butterfly Conservation, Wareham. Oates, M. In prep. Aspects of the ecology of the Pearl-bordered Fritillary Boloria euphrosyne in Woodland. Butterfly Conservation Occasional Paper, Wareham. Stewart, K. E. J., Bourn, N. A. D., Joy, J. & Roberts, R. E The status, mobility and habitat requirements of the Small Pearlbordered Fritillary (Boloria selene) in Clocaenog Forest. Butterfly Conservation Contract Report to Forest Research Report No. SO2-17. Warren, M. S., Thomas, C. D. & Thomas, J. A The status of the Heath Fritillary butterfly Mellicta athalia Rott. in Britain. Biological Conservation 29,

5 Wyre Forest Study Group Pearl-bordered Fritillary Phil Rudlin 39