Rodents

Kiore, or Polynesian rats, Rattus exulans, arrived in New Zealand either by accident, hidden amid food supplies of the Polynesian people, or on purpose, to be itself a food supply. Kiore rapidly became widespread throughout the country and often reached very high numbers, especially in years of abundant berry or seedfall from the native vegetation. The effects on the native animals are largely unknown, but they probably had a substantial effect on the smaller bush birds, lizards and invertebrates.

Soon after James Cook set foot on New Zealand in 1769, sealing and whaling camps were established and numerous vessels trading for timber and flax began to visit the coasts. Rodents traveled as stowaways on all of the vessels and rapidly spread throughout New Zealand. Plague proportions of mice Mus musculus were reported in some areas as early as 1830. By 1840 wheat-growing attempts near Christchurch had to be abandoned because the crops were overrun by Norway rats Rattus norvegicus. The ship rat Rattus rattus did not become well established until the 1860's in the North Island and the 1890's in the South, however, this species is more arboreal and is a far more effective predator of tree nesting forest birds and its late spread may account for the final disappearance of several bird species from the mainland.