Nesting pairs of brown skuas (Catharacta lonnbergi
), black-backed gulls (Larus dominicanus
), red-billed gulls (Larus novaehollandiae
), white-fronted terns (Sterna striata
), Chatham Island oystercatchers (Haematopus chathamensis
) and shore plovers (Thinornis novaeseelandiae
) were counted during 10 seasons on Rangatira (South East) and Mangere islands of the Chatham Islands. It was concluded that the small numbers of skuas, oystercatchers, and shore plovers on the islands was a result of habitat shortage, but that populations of the colonially-breeding gull and tern were constrained by food limitation in the surrounding seas. Whereas skuas, black-backed gulls, and terns nested in the open with conspicuous nests the other shore species on the islands had concealed nests. Comparison with nesting on Chatham Island, the New Zealand mainland, and subantarctic islands suggested that concealed nesting by red-billed gulls, oystercatchers and shore plovers was most likely in response to the presence on the islands of the predacious brown skua.