Long-term population changes among breeding shorebirds in the Outer Hebrides, Scotland, in relation to introduced hedgehogs ( Erinaceus europaeus)

Abstract

In 1974, hedgehogs ( Erinaceus europaeus) were introduced to the island of South Uist, which forms part of an area holding one of the largest concentrations of breeding shorebirds in Western Europe. By the 1990s these mammals had spread widely and become major predators of shorebird eggs. Breeding shorebirds were surveyed in 1983, when hedgehogs were confined to a small part of South Uist. They were surveyed again in 2000 by when hedgehogs had occupied all of the southern part (South Uist and Benbecula) of the 250 km 2 of lowland shorebird nesting habitat for at least 10 years but had not yet colonised large parts of North Uist and adjacent small islands. Between surveys the overall numbers of shorebirds in the hedgehog-free northern zone increased by 9% but in the southern zone, where hedgehogs were present, numbers decreased by 39%. Population changes differed among species, but for all species the population in the hedgehog-free northern zone outperformed that in the southern zone. The most marked differences occurred in northern lapwing ( Vanellus vanellus) and common redshank ( Tringa totanus), which both showed large declines in the southern zone and moderate to large increases in the northern zone. The north–south differences in population change could not be explained in terms of habitat change and were probably largely driven by hedgehog predation.