Story: Human effects on the environment
Page 4 – Impact on animals
From their first arrival in New Zealand in 1769, Europeans brought animals deliberately (such as pigs, for food) or accidentally (such as stowaway rats). This was the beginning of a new period of extinctions and range reductions for native animals.
Loss of marine mammals
From 1792, sealers arrived to hunt marine mammals, mostly in the southern South Island and subantarctic islands. Whalers followed from about 1800. By about 1850, this brief but devastating exploitation was over, leaving New Zealand sea lions and fur seals exterminated from most of the areas they had occupied before the hunters came. The total number of seals killed is unknown, but more were taken from the Bounty and Antipodes islands alone than the entire fur seal population in New Zealand today.
Effect of introduced mammals
Since the late 1700s, 54 more mammal species have been brought to New Zealand. Nineteen of these, including two devastating predators (the Indian grey mongoose and the North American raccoon) did not become established in the wild. However, 11 predators successfully became naturalised: three more rodents; three mustelids (ferrets, stoats and weasels); pigs, hedgehogs, possums, dogs and cats. These have had a massive impact on the remaining native birds, invertebrates and reptiles. Forty out of a total 91 land birds are now extinct, with many others in serious decline.
Loss of seabirds
Fewer seabird species have become totally extinct, but only because small numbers have survived on islands free of rats, mustelids or cats. The many millions of seabirds that once bred on the main islands have been reduced to just a few small colonies. When kiore (Pacific rats) arrived in New Zealand, they killed the smallest birds such as storm petrels and prions. Larger predators introduced by Europeans attacked larger seabirds – particularly eggs and chicks in burrows. This has also affected soil fertility, as seabirds transport key nutrients such as nitrogen and phosphorus from the sea to the land.
Tally of loss
Sixty-four endemic species of birds, lizards, frogs and a bat have become extinct since humans settled in New Zealand. They succumbed to hunting by people, and predation by kiore (Pacific rats) and 11 other mammals. Over 30 more species survive only on small predator-free offshore islands.
Impact of grazing animals
New Zealand’s forests are now home to 14 wild introduced grazing animals, such as goats, deer and the brushtail possum. These have transformed forest understoreys and regeneration patterns. Some forest trees are very long-lived, so it may be hundreds of years before the effects of browsing by mammals shows in the forest canopy.