The Historic Extinctions

Predation has been hugely significant in the historic decline in New Zealand's native fauna (Innes & Hay 1991; Holdaway 1999; McDonald & Murphy 2000; Worthy & Holdaway 2002), but most of the historical extinctions could not have been the work of stoats—not because they were not capable, but because they had no opportunity. Other predators were the first to find the dozens of colonies of tame, defenseless, ground-nesting, and meaty birds that have since disappeared, not only in New Zealand but also all around the Pacific (Steadman 1995).

Melanesian and Polynesian voyagers and their companions (especially Pacific rats) had discovered almost all island groups in Oceania by about 1000 AD. The present Maori population is descended from Polynesian settlers, who arrived in about 1300. European explorers and their companions (Norway and ship rats, plus shipboard cats and assorted livestock, especially goats and pigs) arrived in an accelerating tide from the 1770s onward (Holdaway 1999).

By the time the first stoats arrived in New Zealand in 1884, the native species had been suffering centuries of irreplaceable losses. During Polynesian times, birds and insects that were flightless, or that nested and foraged on the ground, were the first to disappear, along with lizards and frogs. Rats wiped out the small species, spears and clubs the large ones. The medium-sized birds, especially those that nested in trees, fared a little better, but only for a while.

Then, between the first landings by Europeans in 1769 and the first releases of stoats in 1884, more than another century of further damage had been added by cats, by Norway and ship rats and dogs, and by rapid and drastic habitat modification. From data available, at least 142 separate island populations of native birds are known to have been extinguished from the main and offshore islands (Holdaway 1999; King 2005c). Of these, 114 (80%) were never in contact with stoats. Conversely, stoats have never reached the most important offshore islands (Stewart, Kapiti, Little Barrier, or any of the outlying islands) on which many endemic birds have survived, sheltered from the disturbances on the mainland.

On the other hand, on parts of the two main islands, especially in the rugged southwest South Island (now the Te Wahipounamu World Heritage Area,

26,000 km2), the ancient fauna was still largely intact when stoats arrived. Some populations of birds that are now lost or severely threatened were still hanging on there, and for them the arrival of stoats was the last straw (King 1984b). Stoats certainly contributed, with the help of ship rats (which arrived at about the same time), to the final disappearance of the South Island subspecies of the bush wren, NZ thrush, laughing owl, saddleback, and kokako (King 1984b). No doubt stoats also immediately began to aid the already advanced and still ongoing losses of the kakapo, both subspecies of takahe, at least three species of kiwi (Figure 13.1), plus the kaka and the yellowhead (Figure 13.2). The periodic increases in predation by stoats after beech mast years (Chapter 10) may explain why the South Island kokako, which lived mainly in beech forest, disappeared while the North Island kokako, which lives mostly in nonbeech forests, has survived into the era of effective predator management (Clout & Hay 1981; Innes et al. 1999).

These grim figures do not mean that the colonizing peoples and their animal companions were unusually rapacious, only that long-isolated island faunas are extremely susceptible to invasion and losses of endemic species cannot be made good from elsewhere. Invasions by commensal rodents were accidental and could not have been prevented, but the deliberate addition of stoats and common weasels to the list of immigrants has arguably made the tragedy far worse. It is all the more sad because the consequences were predicted by conservationists at the time. Their warnings were ignored, and the legislation they proposed to prohibit the import of mustelids was opposed by powerful economic interests (Hill & Hill 1987).

Figure 13.1 Young kiwi (<800 g) are too small to defend themselves from stoats and, consequently, stoat predation on young kiwi is a serious threat to contemporary kiwi populations in New Zealand.
Himantolophus Azurlucens

Figure 13.2 Predation by stoats has contributed to the continuing, severe decreases in populations of yellowheads, kakapo, takahe, and saddlebacks from the late nineteenth century onward. Kakapo and saddlebacks no longer survive on the New Zealand mainland at all; yellowheads and takahe do so only in some protected areas.

Figure 13.2 Predation by stoats has contributed to the continuing, severe decreases in populations of yellowheads, kakapo, takahe, and saddlebacks from the late nineteenth century onward. Kakapo and saddlebacks no longer survive on the New Zealand mainland at all; yellowheads and takahe do so only in some protected areas.

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