Kapiti rat blitz

Forest and Bird, Issue 281, 1 August 1996, Page 4

Kapiti rat blitz

BY THE TIME you read this, New Zealand’s largest rat eradication should have taken place. At the time of writing in mid-August, DoC staff had closed Kapiti Island to the public and were watching the weather for the best time to drop the 26 tonnes of poisoned bait needed to remove the island’s last two mammalian predators — Norway rats and kiore. Under consideration for four years, the eradication is now considered operationally feasible on the 1,960-hectare island. No other area of this size anywhere in the world has been successfully cleared of rats, and the procedure is complicated by the need to wipe out the two species at the same time. Weka, since they eat rats, are the only birds likely to be affected by the poison in any numbers. A hundred of the estimated 2,000 weka on Kapiti have been put into four pens on the island where they will be held until the baits have decomposed. Another 140 have been removed to the mainland. It is expected the Kapiti weka population will be back to full strength within five years. Although the eradication

cannot be officially considered successful until the island has been monitored for rats for two or three years, DoC regional conservator Allan Ross expects to see a rapid increase in birdlife in the important wildlife sanctuary following the poison drop. "Some of our rarest native birds such as saddleback, stitchbird, kaka and brown teal are currently suffering massive predation losses to the rats," said Ross. "Even those birds which can uneasily coexist with rats such as tui, bellbirds and robins, plus a colony of longtailed bats, will also benefit from the rodent removal." Once the rats are removed, DoC will need to increase efforts to prevent any accidental introductions. Ecologist and expert on rodent impacts, Dr Ian Atkinson, says that the removal of Norway rats might make the island more susceptible to the invasion of the dreaded ship rat — a better swimmer and more agile climber. "The occasional ship rat that currently lands on Kapiti may have been killed by the resident Norway rats," Atkinson told the Wellington Conservation Board. Atkinson was particu-

larly worried about the risk of ship-rat invasion from the four slipways that exist on Maori land on the northern end of the island. He also argued that a private commercial lodge proposed on Crown land between the Maori land and the nature reserve would generate a continuous flow of foodstuffs, stores and building material all of which increase the risk of rat introduction. No decision on the lodge can be made until complicated tenure issues relating to the status of the land are sorted out by the Commissioner of Crown lands.