CAUSES AND EFFECTS OF LATE HOLOCENE VERTEBRATE EXTINCTIONS IN NEW ZEALAND

The end-Pleistocene glacial-interglacial transition (14-10,000 b.p.) was not accompanied by a vertebrate extinction event in New Zealand. However, a major vertebrate extinction event involving both megafauna (fur seals, sea lions, birds) and microfauna (large invertebrates, frogs, lizards, a sphenodontid, birds) began some time after 2000 b.p., intensified briefly after 700 b.p.(when settlement by Polynesians began), and was renewed after 200 b.p. (after European settlement).

Each phase of the event followed the introduction of additional mammalian predators, including man. The size range of taxa associated with each extinction phase was related to the body size and habitat of indigenous species and introduced predators. Nearly all small (< 1000 g) taxa vulnerable to predation by the Pacific rat (Rattus exulans) were extinct before 1779 AD and almost all megafaunal species (> 5 kg body mass) are known to have survived until Polynesian settlement but were extinct before European settlement. The extinctions occurred during a period of stable climatic or vegetation patterns. There is no evidence for epidemic disease.

Large deposits of megafaunal remains – sometimes representing >10,000 individual moa, Aves: Dinornithiformes) – are associated with early (14th century AD) Polynesian settlement sites, particularly in the South Island, but not with later (post-1500 AD), “Classic” Maori sites. Extensive anthropogenic environmental degradation in eastern areas of both islands contributed to, but did not itself cause, extinctions. Extirpation of large populations (possibly billions) of small petrels by Pacific rats is likely to have affected the terrestrial food webs on the main islands of New Zealand and oceanic food webs in the south-western and northern Pacific Ocean.