Above picture: The Mouse-Free Marion Project’s Operations Manager, Keith Springer, presenting a talk at the 31st Vertebrate Pest Conference in Monterey, California, USA in March 2024
In November 2023, the Mouse-Free Marion (MFM) Project initiated and co-organised a Mouse Eradication Workshop in Palmerston North, New Zealand. The workshop, attended by Anton Wolfaardt, MFM Project Manager and Keith Springer, MFM Operations Manager, was conceived to gather experienced eradication practitioners and consider potential reasons for the failure of two recent mouse eradication projects – Gough Island (South Atlantic) in 2021 and Midway Atoll (North Pacific) in 2023.
The MFM Project team has a strong interest in the outcome of these projects, because they were two of the three islands where invasive House Mice Mus musculus have been observed to prey upon the chicks and adults of breeding seabirds. Because Marion Island is the third such island where this occurs, and where eradication is still being planned, we wanted to understand which factors might have contributed to these failed outcomes, and to learn what we could from the experience of the project teams that implemented the two projects in order to refine our planning.
It was not clear (and still isn’t) whether the commonality of these islands where mice prey upon seabirds was a core factor in the failure to achieve mouse eradication. But, if it was, we need to understand what we could do differently if we are to succeed on Marion Island. This provided the impetus to get the Mouse Eradication Workshop underway, and gain insights into what may have contributed to eradication failures on Gough and Midway. This had to be considered in context though, and the relevant context was that for the previous 15 years, nearly all mouse eradication projects that used the same method (aerial distribution of rodenticide bait) had been successful.
The “in-person” attendees at the Mouse Eradication Workshop, Palmerston North, New Zealand, November 2023; photograph by Iain Rayner
The Palmerston North workshop drew 26 participants from six countries in a hybrid format, with 18 attending in-person and the remainder participating on-line. The workshop was structured around discussing three key hypotheses:
- That mice could not eat bait (not available for various reasons including insufficient application rate or competition with non-target consumers).
- That mice would not eat bait (palatability or bait composition issues, alternative preferred food sources).
- That bait toxicity is a problem (mice needing a higher toxin concentration to ingest a lethal dose of bait, especially if in conjunction with 1 above).
Discussions around these hypotheses considered information from both the Gough and Midway mouse eradications, and from contributing planning and review documents. Participants sought to understand what might have changed in these two eradications after a long period of successful operations where these three hypotheses had not been apparent issues preventing the success of mouse eradication operations; whether this circumstance was merely a coincidence, or whether some new factor had emerged that was contributing to eradication failure.
The fact that some mice on Midway and Gough (and Marion) had learnt to prey on seabirds was a primary consideration, and lead to much discussion about how to conduct eradication projects when mice may be habituated to protein as a food source, that they would usually obtain from feeding on invertebrates.
A House Mouse on Marion Island; photograph by Ben Dilley
In March 2024, the 31st Vertebrate Pest Conference was held in Monterey, California. The MFM Project was represented by Keith Springer who delivered a co-authored presentation titled “Factors contributing to recent house mouse eradication failures on islands: An initial assessment following a workshop in New Zealand”.
The presentation focused on outlining the core hypotheses discussed at the workshop in November 2023 and the initial findings from those discussions. The value of international collaboration was also emphasised, with ongoing liaison between staff from different institutions across different countries working towards various outputs from the workshop. These include updating the New Zealand Department of Conservation’s Best Practice for Mouse Eradications Using Aerial Baiting document, and initiatives to identify and allocate research topics to better understand what may improve the success rates of eradication success in future mouse eradication projects.
Symposia topics at the Vertebrate Pest Conference included management of pest birds, predators, commensal rodents, feral pigs and vertebrate toxicants. Several presentations were of relevance or of interest to the MFM Project, including presentations on the use of drones on island eradication projects (although not something likely to be suitable for use on an island the size of Marion), non-toxic rodent control methods, including gene editing (not likely to be an available tool in time for Marion), fertility control (some treatments need to be repeated four times annually), new rodenticides being developed, monitoring methods and rodent behaviour, and an update on the Midway Atoll mouse eradication attempt.
Other than attending a range of interesting and informative presentations, useful connections were made with other conference attendees who are involved in rodent control or eradication work. Participation in the New Zealand and California events has contributed to the MFM Project’s planning towards the successful eradication of Marion Island’s introduced mice.
References:
Broome, K., Callender, A., Griffiths, R., Le Bouard, F., Shiels, A., Springer, K., Thomas, S., Will, D. & Wolfaardt, A.C. 2024. Factors contributing to recent house mouse eradication failures on islands: an initial assessment following a workshop in New Zealand. 31th Vertebrate Pest Conference, March 11-14, 2024, Monterey, California. 18 pp.
Abstract: Invasive house mice (Mus musculus) threaten native biodiversity on many of the world’s islands. Best practice for eradicating house mouse populations from islands currently relies on bait containing the anticoagulant rodenticide, Brodifacoum. These baits are typically either broadcast (by hand or by helicopter in natural areas) or placed in bait stations (in human infrastructure or in areas where aerial broadcast is not permitted). There have been many successful mouse eradications using these methods, including 29 of 36 attempts of islands being successful (81%) in New Zealand alone. Following recent failed mouse eradications on Gough Island (South Atlantic, 2021) and Midway Atoll (North Pacific, 2023), a workshop was convened with 24 people attending (16 in-person, 8 on-line) from seven countries (Australia, Canada, France, NZ, South Africa, UK, US), to discuss some hypotheses for what may have contributed to these unsuccessful outcomes. The workshop was held in Palmerston North, New Zealand, between November 27 and 29, 2023. Discussions over the three days revolved around these hypotheses. We present the key factors hypothesized for why eradications failed on these two islands. We also outline research and operational needs that were identified in the workshop that can contribute to improved outcomes for future eradications of house mice from targeted islands.
Broome, K.G., Golding, C., Brown, K.P., Horn, S., Corson P. & Bell, P. 2017. Mouse Eradication using Aerial Baiting: Current agreed Best Practice used in New Zealand (Version 1.0). DOC-3034281. Wellington: Department of Conservation. 23 pp.
Keith Springer, Mouse-Free Marion Project Operations Manager, 25 April 2024
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A Wandering Albatross rests beside its chick on Marion Island; photograph by Sean Evans and poster design by Michelle Risi
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.
