Balancing the risks with the benefits

The Kotuku peninsula restoration programme has been a huge undertaking.

After 8 years of trying to control animal pests to low enough levels where their effects on native species were minimised we found that the costs of trying to do this were unsustainable. Funding as well as people resources are very difficult to maintain over a long time frame.

After completing the pest proof fence in 2008 we embarked on a programme to eradicate the animal pests. This has involved the use of a range of techniques including Pestoff 20R, a cereal based bait containing the toxin brodifacoum which is highly effective against rodents. The baits are about 2g in size and are dyed green to deter birds. Brodifacoum is insoluble in water.

Aerial application of the bait was undertaken at Kotuku in order to get bait into every rodent habitat and ensure an even rate of spread which is essential to get every last rodent. Hand broadcasting was undertaken around and under houses. If we had undertaken this programme by ground it would have required the cutting of an extensive track system and bait stations every 10m in order to eradicate mice. It would also have required considerably more bait than with an aerial drop.

The aerial operation is being followed up with an intensive ground based monitoring programme designed to detect any remaining pests and remove them as quickly as possible. A 50x50m tracking tunnel grid of 1100 tunnels records prints of small pests. This is being checked monthly. If tracks are detected these areas are intensively targeted with traps and bait stations until no more tracking is recorded. This system is further supported by bait stations and traps around the outside of the fence to catch re-invaders prior to them hitting the fence ends. Experienced hunters are also being employed to assist with the detection and removal of the last rabbits, cats and pigs if any.

This system allows us to respond as quickly as possible to any signs of pests. Already only 2 months after the eradication programme was started we are seeing results. One rat was tracked under a house at Arthur’s Bay but this appears to have been dealt with.  No rabbits have been seen and we are currently confirming this with a professional hunter who is also looking for cats and pigs.

However we have had some losses. We lost a number of pukekos, sparrows, mynahs, 3 ruru and 2 pateke. Although unfortunate the loss of ruru is a benefit for the robins. In the 2007 breeding season we lost two females to rats on the nest and then one off the nest to an unknown cause. This left us with one female and four males. The female nested with three of the males but the two chicks that were hatched were taken by moreporks. The adult robins are usually able to avoid morepork predation but they consistently loose eggs and chicks. With the new breeding season underway we have already sighted several juvenile robins on the peninsula during our rodent monitoring runs.
 
Ruru are territorial birds and any vacancy created will soon be filled by other moreporks. Evidence from other similar bait drops shows that morepork populations increased in all the study areas (their chicks are also predated by rats and cats).

The loss of 2 pateke is unfortunate. As a precaution we discontinued hand feeding around the house over a year before the bait drops were due to occur. We didn’t find any sign of pateke when we visited the usual habitats while we were checking the 50m x 50m grid of monitoring lines in advance of the bait drops. An aerial survey was conducted beforehand as well and no pateke were seen. (As a comparison 12 to 13 pateke are known to be lost to road kill on Great Barrier each year and the chicks hatched along the foreshore are always lost to black backed gulls). We expect that releasing pateke from cat and rat predation on the Peninsula will result in an increase in numbers around the wider Port Fitzroy area. Pateke have already been sighted again inside the fence.

Pukeko will also quickly recover. At Tawharanui Regional Park where a similar operation was undertaken pukeko recovered to their pre eradication numbers within a year. At Kotuku the reduction in pukeko numbers will also help pateke as they are known to predate juveniles.

We will continue to monitor the progress of the eradication programme and report the risks and the benefits honestly and accurately as we know them. While it is not ideal that we have lost some native species, we know from the experience of other restoration projects such as Tiritiri Matangi, and Tawharanui Open Sanctuary that the benefits far outweigh the risks. The small numbers of native species that are affected quickly have their numbers replenished in the absence of predators. If we can sustain the removal of pests from Kotuku it’s likely other native species such as kakariki and bellbird may naturally return and that in time other lost species such as kokako and saddleback may be reintroduced.

Caroline Leys living on the outer edge of the Kotuku Peninsula made the following comment:

“We are absolutely delighted with the results even though the ruru are very dear to us and we will miss them. All the bait has now vanished from our property. We have a nesting pair of kaka for the first year, I guess soon we will be cursing them for stripping our fruit trees! The bush is full of seedlings and we have oyster catchers, grey warblers, tui, finches, kingfisher and fantails sounding all day. We also have herons stalking the coast now, and regularly on the shore at Orama. This is really very different to 10 years ago when there were only grey warblers in the dawn chorus on our property.”

We are on the lookout for volunteers to help with the rodent monitoring which we do once a month so would appreciate any offers of help in this regard. Volunteers need to be fit and bushwise. Please contact Tony Bouzaid on 09 4290091.