Individual study: Eradication of house mice Mus musculus by aerial and ground-baiting to facilitate recovery of endemic species, Mana Island, Wellington, New Zealand
Newman D. (1994) Effects of a mouse, Mus musculus, eradication programme and habitat change on lizard populations of Mana Island, New Zealand, with special reference to McGregor's skink, Cyclodina macgregori. New Zealand Journal of Zoology, 21, 443-456
Mana Island is a small island situated of the coast of Plimmerton located at the southern end of the North Island of New Zealand. Mana Island is home to many different plant and animal species both native and introduced. In the past it was farmed intensively for cattle and heavily grazed but in the 1980s, the restoration potential of the island was recognised and all livestock were removed. Unfortunately cessation of grazing allowed the introduced grasses to flourish, flower and seed. Subsequently, the introduced house mouse Mus musculus population rocketed to the detriment of several lizard species. The last recorded sighting of the gold-striped gecko Hoplodactylus chrysosireticus was in the late 1970's, and was then thought extinct, whilst the population of McGregor's skink Cyclodina macgregori was in steady decline. Pitfall trap monitoring of surviving lizard populations turned up many half chewed lizards, preyed on by mice. Eradication of mice from the island was therefore considered necessary to enable lizard populations and other biota to survive and hopefully recover.
Ground & aerial baiting: Mouse eradication was carried out by aerial poison drop and ground baiting in 1989/1990. A 25 m grid of bait stations was set up over the entire island. The bait stations were initially baited with 16 g Storm wax blocks (0.005% flocoumafen) on 26 & 27 July 1989, and were maintained with a combination of Storm, Talon 50WB and Kiwi-Care Waxy-pack baits through to February 1992. One tonne of 4 g Storm wax pellets was dropped by air from a helicopter on to the cliffs around the island on 24 July 1989, and two tonnes of Talon 20P pellets (0.002% brodifacoum) were dropped over the entire island on 4 September 1989. No other species mortality at population level was recorded as a result of the poison.
Monitoring: The skink population was monitored throughout and after the baiting. There is ongoing rodent monitoring to ensure that mice and other rodent pests do not return unnoticed.
The last mouse was caught in February 1990 and no other introduced predators have subsequently been recorded on the island. The population of McGregor's skink has increased and they have became more widespread over the island. The gold-striped gecko was rediscovered in 1993 almost 25 years after the last recorded sighting. These geckos were eventually found in significant numbers and persisted in several colonies. Other species e.g. flightless heavy invertebrates such as giant weta Deinacrida rugosa(Orthoptera) also flourished after the mice were eradicated. Since then, other endangered endemic species have been transferred to the island e.g. takahe Porphyrio mantelli (a flightless bird) and the flightless flax weevil Anagotus fairburni.
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