The eradication of mammalian predators from Quail Island, Banks Peninsula, Canterbury, New Zealand

Abstract

In the period from January 2000 to January 2003 an attempt was made to eradicate mammalian pests (rodents, mustelids and hedgehogs) from Quail Island (Otamahua) to allow re-introductions of native species that were once present. Eradication techniques involved live trapping, kill trapping using Fenn traps and night searches that removed a total of 353 individuals. A ground-based poison operation was also undertaken. During 2 - 9 August 2002, 555 bait stations (yellow and black) were placed at 40m intervals covering Quail Island. Stations were baited with Pestoff 20R rodent bait pellets (0.002% brodifacoum) and, at later stages of the operation, Talon 50 WB briquette (0.005% brodifacoum). An analysis of predominant vegetation surrounding stations was also undertaken.

Exotic grassland was the dominant habitat where hedgehogs were trapped and found during night searches. Hedgehogs were caught more readily on or near tracks, which they presumably use to feed and travel around the island. Male rats made up 70% of the rat catch. Bait-take by rodents was highest from black bait stations and from scrubland habitats surrounding bait stations on Quail Island.

Eradication could not be confirmed, as a few bait stations were still active but most, if not all damage, appears to be by ground (Hemiandrus sp.) and cave weta (Pleioplectron simplex Hutton). Furthermore, a few hedgehog scats have been found since the poison operation began and no hedgehogs have been observed or trapped for 18 months indicating they have become vary scarce or have been eradicated. This information will be important for future management of Quail Island due to the proximity of the mainland, via mudflats, will need ongoing vigilance to protect against pest reinvasion.