The importance of the introduced hedgehog (Erinaceus europaeus) as a predator of the eggs of waders (Charadrii) on machair in South Uist, Scotland

Populations of waders (Charadrii) on machair habitats on the island of South Uist were counted and wader nests were monitored to determine nest success and causes of failure. There were large declines in wader numbers and nest success following the spread of the introduced hedgehog throughout the island. Predation of wader eggs by hedgehogs was frequent, but susceptibility varied among wader species, being between 0 and 60{%} of the nests started. Wader species that were susceptible to hedgehog predation tended to suffer larger population declines than those that were less susceptible, with the exception that the ringed plover (Charadrius hiaticula) population declined markedly even though their nests were depredated by hedgehogs infrequently. A combined analysis of mark-resighting and radio-tracking data produced an average hedgehog population density estimate of 57 adults km−2. It was estimated that wader eggs only provided 0.7–5.5 % of the energy requirements of hedgehogs, even during the season when most eggs were taken. From this it is argued that the abundance of hedgehogs and the intensity of their predation on wader eggs are unlikely to diminish in response to wader population declines. Unless some presently unidentified density-dependent mechanism compensates for low nest success, local extinctions of susceptible wader species are likely if no action is taken to reduce hedgehog predation. This appears to be the first documented case of hedgehogs threatening an internationally important bird population with regional extinction.