Above picture: Soon the mice will be gone. Filling the bait bucket on Antipodes Island
Note: Keith Springer, the Mouse-Free Marion Project’s Operations Manager, has over 20 years of experience in the field of eradicating introduced mammals on Southern Ocean islands. Most notably he led the Macquarie Island Pest Eradication Project (MIPEP) from design to completion over 2006-2015. As well as his roles on sub-Antarctic islands, he has also been involved in an advisory or an operational capacity with rodent eradications on seabird islands in both hemispheres, including Alaska’s Hawadax, Italy’s Tavolara and Australia’s Lord Howe.
In his invited essay that follows he gives his thoughts on the need for this work and just what is required to achieve success.
A key feature of remote oceanic island-dwelling wildlife is that species have evolved in the absence of terrestrial mammals. Prior to the expansion of human exploration and exploitation, land-based mammals never had the means to reach far-flung oceanic islands. The upshot of this is that many species of plants, invertebrates and birds evolved in isolation from mammals – a group that includes browsers, grazers and predators. With increasing human technology and innovation, and spurred on by a mixture of nationalism, curiosity and profit motives, many hitherto unknown islands in the Southern Ocean were discovered and their resident wildlife subsequently exploited for profit. Mammal species were released on most of these islands deliberately for a subsequent food source (the grazers and browsers), arrived as stowaways or via shipwrecks (the rodents) or as human companions (dogs and cats).
Having evolved in the absence of the mammals, plants and wildlife native to many of these islands were unable to cope with these new stresses to their populations. Species were lost even before they were described by scientists. Some may even have gone extinct before humans were even aware of their existence, especially among the more cryptic invertebrates. Some species not yet globally extinct have been extirpated on breeding islands through the impacts of invasive species. This puts incredible pressure on remaining populations and impoverishes the biodiversity of islands from which they have been lost. Whereas no Southern Ocean seabird species has as yet gone extinct (due to their individual longevity) their low breeding success due to predation (and often for albatrosses and petrels, longline fishery mortality) has many of them staring down that particular barrel.
Put simply, removing introduced predators from islands is one of the most powerful tools available for stemming the decline in global seabird populations. Seabird populations are resilient, even though the impacts of a changing climate and especially rising sea temperatures are testing them in other ways. However, they cannot withstand predation of eggs, chicks and adults on their breeding islands, and still have a viable future.
I have been fortunate, in many ways, to visit and work on a number of sub-Antarctic islands. What I have seen there, and especially what I have not seen – such as dense clouds of wheeling seabirds because there aren’t any left – has reinforced the gravity of the situation facing these birds, and the need for us to help them. However, often the problem is underappreciated and unrecognised on a global scale, because so few people have the opportunity to visit these remote places. More than anything, the advent of trail and burrow cameras has finally given proof of what has been happening year after year for many decades; the slow whittling away of seabird populations as predation by cats, rats and mice has taken its toll.
My first significant involvement in assisting with the removal of introduced pests from islands was as a team leader for the feral cat eradication on Australia’s Macquarie Island. Even before the last cat was removed, Grey Petrels Procellaria cinerea – not confirmed breeding on Macquarie in a century – were discovered breeding. After removal of European Rabbits, Black Rats and House Mice from the island by the Macquarie Island Pest Eradication Project (MIPEP) in 2011 (confirmed as successful in 2014), the very next summer dozens of active Blue Petrel Halobaena cerulea burrows were found on coastal headlands, whereas previously only a handful were present on offshore rock-stacks free of predators. Pintado or Cape Petrels Daption capense are also now breeding back on Macquarie, and other burrowing petrel species such as Soft-plumaged Petrels Pterodroma mollis and Sooty Shearwaters Ardenna grisea are re-establishing themselves. During the early 2000s, with the waning of the effectiveness of Myxoma virus, rabbits grazed the island to the quick, leaving large expanses of bare earth. Within months of their eradication, the island was visibly greening, and now – some 10 years later – the vegetation community is reaching a distribution and abundance previously unknown to anyone alive today.
The South Georgia Heritage Trust achieved a similar outcome on the United Kingdom’s South Georgia in the South Atlantic, another island where I joined the eradication team. Within a couple of breeding seasons of Norway Rat eradication, numbers of South Georgia Pipits Anthus antarcticus, South Georgia Pintails Anas georgica georgica and numerous burrowing petrel species (including storm petrels) were far more abundant.
Likewise on New Zealand’s Antipodes Island, where I was involved with the Million Dollar Mouse project that led to the successful eradication of House Mice in 2016, the endemic Antipodes Island Pipit Anthus novaeseelandiae steindachneri and Antipodes Island Snipe Coenocorypha aucklandica meinertzhagenae have both subsequently increased in abundance.
Similar recovery of sea and other birds has been recorded following many other island eradication projects globally, including in the Mediterranean, Pacific, Caribbean, North and Central America and the United Kingdom.
The empirical and anecdotal evidence is clear. If invasive predators and grazers can be removed from islands, the rebound in native vegetation and wildlife is immediate and dramatic; all the birds need is a chance to breed without being preyed upon.
Eradicating invasive species from remote islands does not come easy. But the physical implementation of the work is the last of three stages and is usually less challenging than the first two stages. Of these, the first is raising awareness of the problem, and generating the political and public will to do something about it, as expressed in successfully raising the requisite funding. The second stage is the multiple years of planning, organising and securing regulatory approvals to undertake the work. It’s a part of human nature that in this stage we invariably encounter people who tell us all the reasons why it can’t be done, as well as those more well-intentioned who do not understand why the eradication cannot be undertaken immediately. Many pieces of environmental legislation and regulations were never written with the scenario in mind whereby invasive species could be removed from islands, using techniques unimaginable when the legislation was prepared, and thus can preclude various activities now vital to the implementation of an eradication programme. Yet to succeed, a way around or through these administrative challenges needs to be found.
Island eradication programmes, especially for rodents, ungulates and cats, have a very high success rate. They are not, and probably never will be, 100% successful. But the high proportion of successes, and the startling recovery of native species once predators are removed, is the proof in the pudding that this work is so worthwhile.
The task of eradicating invasive species needs many things to be successful. Sufficient funding to implement an operational plan is critical. There are no half-measures, so half a budget is of little use. It needs the time to undertake all the planning components to the requisite level of detail. Once on the islands, it is too late to go back for a critical piece of equipment that hadn’t been remembered or thought of. It demands people working on the project to have total commitment, who will do whatever is necessary to get the project over the line. It isn’t a suitable vocation for 9 to 5-ers. It needs people with an unshakeable belief in what they are doing. It needs key supporters, influential people who can champion the project and smooth the way past the numerous regulatory and logistical challenges that will inevitably arise. It needs at least some luck to be on your side, because especially in eradication operations involving flying helicopters in sub-Antarctic weather conditions, the weather can play a make-it-or-break-it role. It needs rigorous peer review, because there is a body of global experience that has been built up over decades, that can help in formulating the particular eradication strategy for an individual island. And it needs experienced people. As in many endeavours, the specialist roles are done best if done by people who have done them before and have already learnt the lessons that contribute to successful outcomes.
Typically, eradication projects are ‘over-engineered’, firstly because we are risk-averse and want to do everything possible to enhance our chances of a successful outcome. And secondly, because these are projects with binary outcomes. We can’t ‘almost eradicate’ an invasive species from an island – we either get the last individual, or we fail. Failed eradications are often difficult to account for a single reason why, so we try and ‘over-engineer’ the project design to cover off against as many potential points of failure as possible. An example of this might be as simple as taking considerably more helicopter fuel than we calculate we would need for a rodent eradication involving aerial distribution of rodenticide bait, simply because if our calculations were out, we can’t go and get more fuel, and the operation would stop in its tracks.
With these aspects in place, and enough political will to act, there is no doubt that the carnage humans have wrought on island biodiversity by introducing alien species can be reversed. Often there are suggestions of active restoration once introduced species are removed, but in general this is rarely necessary – take away the predation pressure and the remnants of the native species will do the rest and restore themselves.
This outcome has been demonstrated many times globally, especially following the eradication of rodents, and we fully expect the same outcomes to be evident after the anticipated removal of House Mice from Marion Island. Marion will be the largest island globally where mouse eradication is being attempted, and it brings specific challenges, especially in the size, shape and altitude of the island, plus the known adverse weather conditions that frequently prevail. Whereas it is largely the lessons learned from previous eradications that make it feasible to even attempt mouse eradication on Marion Island, those same projects demonstrate the likely recovery in seabird and invertebrate populations if we are successful in ridding the island of mice. There is no doubt that the images of albatross chicks with wounds on their flanks or elsewhere on their bodies are a strong motivator in wanting to be involved in the Mouse-Free Marion Project. Hopefully with the experience gained elsewhere, I can contribute to the team striving to achieve what would be a most remarkable conservation outcome.
Keith Springer, Mouse-Free Marion Operations Manager, 11 July 2022
The Mouse-Free Marion Project is a registered non-profit company (No. 2020/922433/08) in South Africa, established to eradicate the invasive albatross-killing mice on Marion Island in the Southern Ocean. The project was initiated by BirdLife South Africa and the South African Department of Forestry, Fisheries and the Environment. Upon successful completion, the project will restore the critical breeding habitat of over two million seabirds, many globally threatened, and improve the island’s resilience to a warming climate. For more information or to support the project please visit mousefreemarion.org.