Although people came to New Zealand relatively late – only about 700-800 years ago – human impact on the land and natural ecosystems has been extensive. The first great impact was from hunting, fishing, and gathering, which caused the extinction of native bird species such as the giant moas and eagles.
However, an even greater threat to the native biodiversity of New Zealand was the introduction of invasive alien species. When Europeans arrived on the islands in the early nineteenth century, they brought with them 34 exotic mammal species (including brush-tailed possums, rabbits, cats, goats, stoats and ferrets) and hundreds of invasive weedy plant species. In conjunction with the impact of hunting (and also extensive habitat destruction), the last two hundred years have witnessed the extinction of 16 land birds, one endemic bat, one fish, at least a dozen invertebrates, and ten plants. Several other species survive only in tiny populations on offshore islands.
Today, invasive species remain an important threat to New Zealand's biodiversity, but large-scale habitat destruction, through deforestation, wetland drainage and ecosystem degradation, represents as serious an issue. In terms of natural habitat, it is estimated that remaining indigenous habitat in more or less primary condition amounts to 35,000 km² of forest (down from roughly 230,000 km²), 15,000 km² of native grassland-scrub, 4,000 km² of wetlands and other aquatic systems, 2,600 km² of smaller island ecosystems, 1,800 km² of alpine systems, and about 1,000 km² of coastal systems, for a total of 59,400 km² (or 22 percent of the land surface of the country).