Mana Island rodent-free

Forest and Bird, Volume 23, Issue 1, 1 February 1992, Page 4

Mana Island rodent-free

MANA ISLAND off the coast near Wellington has been officially declared free of rodents after a successful poisoning programme. The 217-hectare island had been infested with mice ever since they arrived with European farmers in the 1830s. Numbers exploded when stock were removed from the island in 1986 and all the pasture grasses seeded together, providing an abundance of food. Prior to the poisoning the Department of Conservation estimated that the island contained over five million mice. A baiting programme began in 1989 at the instigation of Colin Ryder from

Forest and Bird’s Wellington branch (see Forest & Bird, May 1990). Colin received funding for a Conservation Corps project which included the eradication of the Mana Island mice under the management of DoC. Five and a half thousand bait stations were laid by July that year and it is estimated that 90 percent of the mice were killed in the first month of poisoning. No mice have been seen since the first half of 1990 which allowed DoC to officially claim success last October. The island is now being cleared of bait stations by a small team funded by Rotary. However, the problems of

potential rodent infestation remain. Any rats or mice which reached the island now would thrive on the abundant food supply and the populations could increase dramatically. DoC is therefore examining what steps will be necessary to safeguard the island from accidental reintroductions. A number of permanent bait stations will remain near the main landing area. The Mana branch of Forest and Bird is coordinating a long-term native revegetation programme of the island using local genetic stock. Tens of thousands of trees have been planted and already there has been a significant

increase in bird and invertebrate life on the island. Mana Island is the only island larger than 200 hectares entirely free of introduced mammals and within 50 km of the New Zealand coast. It is also thought to be the first island of its size in the world to be cleared of mice after having been infested with them. It now has the potential to play a significant role as an island refuge for the transfer of endangered native plants and animals, although no decision has yet been made as to which species would be suitable.