Motutapu and Rangitoto February 2010 project update
Operational planning for the eradication of the last seven mammalian pests from Motutapu and Rangitoto may have taken more than a year to complete, but it has paid dividends. Implementation of the first two phases of the pest eradication have gone like clockwork and the project is now well ahead of schedule.
First phase of operation
The three aerial applications of bait undertaken to target rats and mice were carried out on 19 and 20 June, 9 July and 6 August 2009. The excellent coverage achieved, coupled with near perfect weather conditions during and after each drop meant that rodents on Motutapu and Rangitoto were exposed to bait right through the harshest period of the winter, ensuring that the changes of operational success were maximised.
Searching for rabbits on Motutapu
Second phase of operation
The second phase of the operation, which includes follow up work on rabbits, cats, stoats and hedgehogs, was instigated after the second bait drop.
Rabbits
An intensive search effort aimed at locating surviving rabbits began following the second bait drop. The four person rabbit team led by Derek Brown encountered just one live rabbit in two weeks of spotlighting, a spectacular and entirely unexpected result. "We expected the rabbit population to be knocked back by the poisoning, but never to the point of nearly removing the entire population," says Derek.
Incidentally, only one other rabbit has been seen on the islands despite further searches including several sweeps of the island with rabbit dogs. "While it is still early days, the prospects of successful rabbit eradication appear positive," reports Derek.
Stoats
Spotlighting for rabbits on Motutapu
Two weeks after the last application of bait, the islands' stoat and hedgehog trap network was activated. All 1,050 traps have been checked four times now with no stoats detected, providing an earlier than expected indicator that the islands' stoat population may be no longer. "If stoats had been present following bait application, they would have been very hungry and it is more than likely they would have been picked up in the first check of traps", says Kellie Mayo, leader of the stoat/hedgehog team.
Hedgehogs
Hedgehogs have been the great survivors of the suite of pest animals present on Rangitoto and Motutapu and are still present in relatively high numbers on Motutapu. "Hedgehogs have always been somewhat of an unknown quantity because they have not been targeted on this scale in this type of habitat before", says John Nielson who is using specially trained dogs to locate survivors.
Slugs and snails have proliferated in the lush pasture since stock were removed from the Motutapu, providing hedgehogs with an abundant natural food source. "This makes trapping hedgehogs particularly difficult, although we expect trapping results to improve now that stock have returned and the island dries out over summer", says Kellie Mayo.
Cats
Setting a cat trap on Motutapu
Cats are still present on the island but several have now been trapped and a number shot by the rabbit team. "It is possible that we are now dealing with the last few individuals", says Michelle Weakley, leader of the cat team.
Michelle noted that cats seemed to thrive after the bait application because of the availability of animal carcasses. "Interestingly, some cats were eating just the muscle tissue of dead animals and may subsequently not have been at risk of secondary poisoning because brodifacoum does not concentrate in this area of the body", she says.
Rats and mice
Surveillance across the stoat/hedgehog trap grid has failed to detect any mice or rats, providing an early indication that the islands are now free of rodents, although two years of monitoring is required before success can be truly confirmed. This result highlights the importance of being absolutely vigilant when travelling to Rangitoto and Motutapu. Checks of boats, gear and equipment before departing are critical to ensure these pests are not inadvertently reintroduced.