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Rat-free islands are a New Zealand conservation success story, a haven for species that cannot survive alongside introduced predators.
It's a story that began with disaster. Taukihepa (Big South Cape Island) hit headlines in the 1960s when ship rats invaded in a deadly plague. Their irruption caused the extinction of two bird species - the New Zealand snipe and bush wren - and the greater short-tailed bat.
At the time, conservation managers concluded (rather depressingly) that such rat invasions were irreversible. Fortunately, one of the great breakthroughs of New Zealand conservation proved them wrong.
1960-1978: The first island rat eradications were happy accidents, unexpected by-products of local control attempts on mostly small islands, between 1 and 32 hectares in size.
Largest island: Titi, 32 hectares, declared rat-free in 1975.
1977-1992: Deliberate, experimental attempts to eradicate rats from small islands began, using new types of anticoagulant poisons. Initially most operations were ground based and labour intensive, with track networks cut over entire islands and bait stations serviced on foot. Early successes provided the impetus for larger campaigns and, from 1981, islands up to 270 hectares in size were treated.
Largest island: Ulva, 270 hectares, declared rat-free in 1997.
1990-2008: Aerial operations took off, spreading baits by helicopter. From using monsoon buckets in 1990, to today's high-tech mechanical spreaders guided by satellite navigational systems, techniques have evolved to allow the rapid and effective spread of baits over very large areas.
Largest island: Campbell, 11,300 hectares, declared rat-free in 2001.
More than 90 islands, covering 20,000 hectares, are now free of rodents, allowing the restoration of burrow-nesting seabird colonies and the recovery of threatened species.
Rat-free islands are precious storehouses for much of New Zealand's biodiversity.
Towns, D.R.; Broome, K.G. 2003: From small Maria to massive Campbell: forty years of rat eradications from New Zealand islands. New Zealand Journal of Zoology 30: 377-398.
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