The ability of feral goats to become pests is partly a consequence of the process of domestication. Neolithic people selected biological characteristics from wild goats, such as higher intrinsic rates of increase and increased sociability that have resulted in their domestic descendants becoming a particular nuisance when they escape to become feral. Feral goats live in about 11 % of New Zealand, mostly on land reserved for conservation of the indigenous biota. Their uncontrolled densities are usually less than 1 ha-1, but have reached 10 ha-1 in one area.
Feral cats became established on Raoul Island some time between 1836 and 1872; the prey available to them included a great variety of nesting seabirds, few of which are present now, landbirds and kiore (Rattus exulans). Norway rats reached the island in 1921, providing additional prey for cats, but also another potential predator of seabirds. The diet of cats is described from guts and scats collected between 1972 and 1980. Rats are the main food, with land birds second in importance, and seabirds are now a minor item.
Feral goats (Capra hircus) have been hunted intensively every year since 1972 on the 2950 ha Raoul Island to protect the indigenous vegetation. Rumen samples taken from 103 goats shot in 1982-83 showed that a minimum of 48 species of vascular plants, mostly indigenous species, were eaten. Only seven foods—Metrosideros kermadecensis, Coriaria arborea var. kermadecensis, Me/icytus ramiflorus spp. ramiflorus, Rhopalostylis baueri var.
Goats were liberated on Raoul Island early in the 19th century. Attempts to eliminate the goats commenced in 1937 and have accounted for at least 15 000 animals. Since 1972, when annual hunting expeditions began, both the number of goats and the area over which they range have steadily declined and the herd is now almost extinct. Despite these changes, the mean group size of goats in 1981-83 remained the same at 3.19, 2.74 and 3.24 respectively. On average, 19% of goats escaped each encounter with the hunters.