Ecological studies on wading birds (Charadrii) in some upland areas of Britain
Factors affecting the diversity and abundance of wading birds during the breeding season were studied on an area of moorland and marginal hill farmland in part of Upper Teesdale. Several vegetation types, on both peat and mineral soils, were available as breeding sites. Low vegetation height and an open, treeless habitat favoured by most wader species was maintained by a combination of management for grouse moor and sheep grazing. The interpretation of multivariate analyses suggested that vegetation type and altitude were the most important determinants of distribution for Lapwing, Redshank, Snipe, Curlew, Golden Plover and Dunlin. Wader species richness and abundance decreased with altitude, approximately one species being lost for every 100m increase in altitude. Both relationships were independent of vegetation type and were thought to be food-related. Within the marginal hill farmland, fields with a cover of Juncus effusus exceeding 5% had the highest breeding densities of waders and were preferentially selected by Lapwing, Redshank, Snipe and Curlew. The proximate factors involved in the selection of fields by these species were typically associated with wet habitats, e.g. marshy patches, the cover and distribution of J. effusus, and flat areas. Species richness was greatest on the large, wet, unmanaged fields. Only Lapwing commonly bred on the drier hay meadows. Three wader species, Common Sandpiper, Oystercatcher and Ringed Plover were notably restricted to bodies of permanent standing water. Of these only Common Sandpiper were abundant, breeding densities varying in accordance with stream width and the number of shingle banks which were used as feeding areas. The formation of Cow Green Reservoir in 1970 seems to have been responsible for attracting Ringed Plover as a new breeding species to Upper Teesdale. Changes of land use in upland areas have important consequences for many wader species. From a consideration of factors affecting the diversity and abundance of wading birds in Upper Teesdale, the implications of such changes were discussed with reference to the management and conservation of upland areas as habitats for breeding waders.