Habitat selection and breeding ecology of three species of waders in the Western Isles of Scotland
The habitat requirements and population dynamics of Redshank, Dunlin and Ringed Plover on internationally important breeding grounds in the Western Isles of Scotland were studied from 1985 to 1987 using individually colour-ringed birds. Twenty-six habitat types were recognised at four study-sites on South Uist. The temporal and spatial use of the habitats by the three species were quantified. Redshank used a wide variety of pasture, marsh and water's-edge habitats and occurred mainly on "blackland" areas. Dunlin were largely confined to areas of old fallow machair and machair marsh. Ringed Plover occurred almost exclusively on the areas of machair used for cultivation. Redshank did not defend breeding territories and individuals ranged over wide areas. Dunlin and Ringed Plover held breeding territories within which most of their activities were confined. Late in the breeding season the seashore was an important feeding habitat for Dunlin and Ringed Plover. Breeding densities varied markedly between major habitat divisions and appeared to be mainly determined by the availability and quality of potential nest-sites as indicated by their conspicuousness to avian predators. Adults, especially males, nearly always returned to their previous year's nest-site or to close by. Young males bred significantly closer to their natal site than young females. Most birds settled within 4 km of their natal site. Breeding success, first-year and adult survival, and the age of first’ breeding were evaluated. The data were used to predict population trends, which were compared to results from large-scale population surveys. It is concluded that Redshank and Dunlin numbers are approximately stable but that Ringed Plover are decreasing. Avian predation was the main factor limiting productivity. Both early season and well concealed/camouflaged nests were more likely to be successful.The conservation of these birds is discussed and some measures suggested that might increase their productivity.