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A BTO Research Report No. 329

Breeding Wader Populations in the Severn & Avon Vales Natural Area in 2002

(EXTRACT)

Authors
Andy Wilson and Mike Smart

Report of work carried out by The British Trust for Ornithology under contract to the
Environment Agency and English Nature

June 2003

© British Trust for Ornithology

British Trust for Ornithology, The Nunnery, Thetford, Norfolk, IP24 2PU
Registered Charity No. 216652

• A total of 72 sites were surveyed for breeding waders in the Severn and Avon Vales Natural Area in 2002.
• 196 pairs of waders were located: 109 pairs of Lapwings, 45 pairs of Redshank, 34 pairs of Curlew, seven pairs of Oystercatchers and one pair of Snipe.Counts were compared with a previous survey. Wader population changes between 1982 and 2002 were in line with those elsewhere, as indicated by the national Breeding Waders of Wet Meadows surveys in those years. Comparison with a RSPB survey from 1995 indicate that the declines have not halted during the last seven years; Redshank in particular is rapidly decreasing in the Severn Vale, and away from the estuary is now found almost exclusively on artificial gravel pit-type sites.Densities of Lapwing and Redshank are only one-third of the average found on wet lowland grassland in England and Wales in 2002, Curlew densities in the Severn and Avon Vales were higher then the national average.Oystercatchers have colonised the Severn Vale within the last 10 years but remain scarce.The only site in the Severn or Avon Vales that attracts drumming Snipe annually is Ashleworth Ham.Efforts to stop and reverse these declines should initially concentrate on safe guarding existing wader populations, through conservation measures at near-natural sites such as the Great Hay Meadow, Coombe Hill, the Chelt/Leigh Meadows, Gooseham and Aysham, and Eckington Marshes. Particular attention should be devoted to the Carrant Catchment, hitherto neglected.Observations in 2002 indicate that Curlew young could be vulnerable to hay cutting well into July, delaying cutting would be beneficial to this species.
• Long-term strategies for wetland recreation in the Severn or Avon Vales should be strongly influenced by the habitat requirements of breeding waders. It should be noted that an element of arable land is important in providing nest sites for Lapwings.

1. INTRODUCTION

Land use changes in river floodplains have come under increasing scrutiny in Great Britain, and in lowland England in particular, in recent years. An increased prevalence in the flooding of built-up areas coupled with a loss of biodiversity along river flood plains have prompted debate about the way in which our floodplains are managed.

Loss of biodiversity on floodplain grassland has been widely reported and ties in with a general loss of biodiversity on farmland across the UK, widely attributed to increased agricultural intensification. Changes in grassland management have been especially pronounced since the mid 1970s, with drainage, re-seeding of permanent pasture, increased use of fertilisers, conversion to arable and changes in stocking regimes all known to have adverse effects on wildlife. Of the bird species found in these habitats, it is the waders that are widely perceived to have been most affected. Substantial proportions of the breeding populations of Lapwing Vanellus vanellus, Redshank Tringa totanus, and Snipe Gallinago gallinago in particular have traditionally been found on wet grassland sites; the reduction or loss of these grassland populations have therefore contributed to local extinctions across some parts of lowland England and Wales.

The changes in floodplain use and management of the Severn and Avon Valleys have reflected those witnessed across lowland Britain. The adverse effects on the Severn catchment’s breeding wader populations have been pronounced. During a national survey of breeding waders on wet grasslands carried out by the British Trust for Ornithology (BTO) in 1982 (Smith 1983) it was found that most areas in the Severn Valley held very few breeding waders. A more extensive survey by the Royal Society for the Protection of Birds (RSPB) in 1995 revealed that wader numbers had dwindled still further (Quinn 1995).

A comprehensive appraisal of options for the re-creation of River Severn/Avon floodplain wetlands was carried out on behalf of the Environment Agency, English Nature and RSPB in 1999. This report (henceforth referred to as Ecoscope) gave detailed information on the history of drainage and land management within the Severn and Avon Vales Natural Area and identified 18 areas (Ecoscope Zones) for potential wetland recreation (Table 1.1). Sites were assessed for their suitability for re-creation of floodplain wetlands based on criteria such as constraining factors (e.g. housing, transport infrastructure, archaeological features, flood defence considerations), habitat requirements (e.g. soil type, water supply, existing habitat) and their suitability for target species groups.

A second national Breeding Waders of Wet Meadows was planned by BTO on behalf of the RSPB in 2001. It was thought worthwhile achieving an extensive survey of the Severn and Avon Vales again in 2001 in the light of the Ecoscope report. This survey was postponed in 2001 due to the Foot & Mouth outbreak but went ahead in the spring of 2002.

This report presents the findings of the 2002 wader survey in the Severn & Avon Vales (henceforth called BTO02). The results for each site are presented and comparative figures for areas surveyed in 1982 and 1995 (henceforth called BTO82 and RSPB95 respectively) are given to provide evidence of changes in wader numbers over the last 20 years. Maps of the distribution of 2002 and 1995 survey sites can be found in Appendices 4 and 5 respectively, along with a map of Ecoscope Zones in Appendix 6.

2. METHODS

Site Selection

The aim was to cover all suitable wet meadow sites within the Severn and Avon Vales in 2002. This was to be done by a combination of volunteer BTO surveyors and a professional surveyor. Priorities for coverage were the Ecoscope Zones and the sites for which previous survey data was available (BTO82 or RSPB95). Due to the complex nature of overlaying results from three sets of site boundaries (BTO82, RSPB95 and Ecoscope Zones), some sites were merged or split to ease survey coverage. Sites covered along the River Leadon were not included in the survey as these were not covered in the original BTO survey and only a single pair of breeding waders (Lapwings) was found in RSPB95. The Carrant catchment, not covered in previous surveys, was covered in BTO02, as were some recently created gravel pits. The final list of sites to be covered comprised over 70 areas of varying size, totalling around 120 square kilometres.

Field Surveys

The methodology followed that from previous surveys (Smith 1983) with three visits to each site between mid April and late June. This spread of visits ensures that at least one visit coincides with the peak activity of each species. The survey method is the “field by field approach”, whereby the observer walks across the site, aiming to walk within 100 metres of the whole area, mapping the locations of waders on large-scale maps. A set of survey instructions can be found in Appendix 12.

Analytical Methods

Wader numbers for each site were estimated using established protocols (O’Brien & Smith 1992; Gilbert et al. 1998) for each species (Table 2.1).

In some cases (e.g. pairs of Redshanks at Saul Warth or Twyning Green) these protocols produced population estimates that were considered to be optimistic by the observers concerned but using these established methods does allow direct comparability with previous surveys.

Each of the site boundaries from the BTO82, RSPB95, BTO02 surveys and the Ecoscope study were digitised so that the data could be analysed using ArcView Geographic Information System (Environment Systems Research Institute 1996). This approach ensured that comparisons of wader counts between surveys referred only to those areas of each site that were covered in both surveys.

3. RESULTS

3.1 Survey Coverage

Seventy-two sites were surveyed (Table 3.1), including all those likely to support breeding waders. The total area covered was 11,868 hectares, considerably more than in BTO82 and RSPB95 (6446 hectares in the Severn and Avon Vales). Most of the sites covered in BTO82 were re-surveyed, giving a sample of 27 sites covering 4653 hectares from which to make paired comparisons while 53 of the RSPB95 sites were covered, totalling 6295 hectares.