Pest Eradication

Pest Eradication Subantarctic Islands
A priority for restoring the islands’ ecosystems is the removal of the invasive mammal species that were introduced in the late 1800s. We plan to eradicate the rats, mice, and rabbits using the standard techniques developed in New Zealand and now practiced worldwide in the fight against invasive pests. The operation involves the dispersal of cereal pellets laced with a common rodenticide, brodifacoum. The baits will be hand-cast along the coasts of Bense and Little Bense, and also along transects across the interior of the islands. The key to a successful operation is to ensure every rodent has access to the poisoned pellets within the range in which it normally moves. Rats have relatively large home-ranges and are therefore are easy to “cater” to, but mice present a more difficult problem. Because mice have such restricted home-ranges, the bait application has to be particularly dense if one wants to ensure each mouse encounters a pellet on its nightly foraging. Bense and Little Bense Islands are the first in the Falklands where mouse eradication will be attempted.

There is a small risk that non-target species will be affected, but similar operations elsewhere have shown this is minimal. Vultures, gulls, and caracaras are all carrion feeders and can be harmed by eating a poisoned rat. However, because they are diurnal predators, they are unlikely to encounter any poisoned rodents, which are active only at night and usually die underground in their burrows.

SAFER’s eradication operation is scheduled for August 2016. Late winter is the best time to do this as there is very little natural food available to the rodents, thereby increasing the chances they’ll dine on one of our bait pellets. The logistics of importing, storing, and then accurately deploying almost 4000 kg of cereal pellets is complex but, if done correctly, the islands will be pest-free for the first time in over a century. The Falkland Islands Government has very generously offered to donate all the cereal pellets needed for this operation.

Update – Pest Eradication Plan Implemented!

During August and September 2016 SAFER was busy clearing the invasive species from Bense and Little Bense Islands. Peter Carey directed the operation with the assistance of two teams of local Falkland Islanders.

Like most eradication operations, this one used cereal pellets laced with brodifacoum to kill the pest species. The Falkland Islands government generously donated the pellets, using surplus stock from the eradication operation on South Georgia. This was spread by hand across both islands (145 hectares / 358 acres in total) in two distinct applications. For the first application, Dr Carey was joined by Toby Poole, Johnny Henry, Lee Hartnoll, and Spurs Henry. Using handheld GPS units to navigate along specific transects, the bait was meticulously distributed in a tight grid pattern. The goal was to ensure every individual rodent would have access to the bait. The presence of mice complicated this process since mice don’t often roam very far when looking for food. To be sure they had a chance to encounter pellets, baiting transects were placed only 20 metres apart instead of the usual 50-metre interval used for rat-only islands. As a result of such close parallel baiting lines, each team member ended up walking 15-20 km a day as they criss-crossed the islands. It took 8 days for the team to cover both islands completely, including extra coverage along the coasts. Bense and Little Bense are only 200 m apart and at low tide it is easy to walk across on the rocky reef between them. This proximity also makes it easy for rats to move between islands so both islands needed to be treated similarly, and simultaneously.

In open country, like that covered by diddle-dee (Empetrum rubrum) and white grass (Cortaderia pilosa), throwing bait while walking a straight line was easily done. However, in dense tussock grass (Poa flabellata) this process became quite testing. Little Bense in particular has extensive stands of dense tussock that slowed progress and drained energy. It is hard enough to climb through 2-metre high tussocks, but when you’re also carrying 15 kg (35 lbs) of bait in a bucket, the task becomes even more challenging. The north coast of Little Bense is wreathed in the densest tussock, and it is also cut by over a dozen small chasms which dramatically complicate the coastline. For this portion of the operation, the team were joined by Bill Pole-Evans of Port Howard, who used his small boat as a mobile baiting platform. This allowed the team to efficiently cover the most challenging parts of the coast.

Eleven days after completing the first application, the second round of baiting began with a new team comprised of Sacha Cleminson, David Hewitt, and Peter Carey. With fewer people the goal was not to repeat the overall coverage of the first application, but rather to give supplemental coverage to the priority areas of dense tussock and the coastlines. The second team took 7 days to re-bait these crucial areas, again using the help of Mr Pole-Evans and his boat to reach the difficult north coast of Little Bense.

The operation on Bense and Little Bense has implications beyond just these islands. This was the first eradication attempt in the Falklands to target 3 species at the same time, and also the first to go after mice. These efforts may therefore provide valuable lessons to assist future eradications on larger, more important wildlife islands like New Island and Steeple Jason.

It will take more than a year to know if the operation was a success. But if all rodents have been removed from these islands, the native flora and fauna of the Falklands will once again flourish here.

Acknowledgements – Although the bulk of this project has been self-funded by SAFER, the Foundation is also pleased to acknowledge support from the Environmental Planning Department, Falkland Islands Government, for the donation of bait and a grant from the Environmental Studies Budget, from Falklands Conservation, for the award of a Small Grant, and from the Encounter Foundation, New Zealand. Thanks also to Kay McCallum, Bill and Shirley Pole-Evans, and BFSAI and the Ministry of Defence for key logistics support.