Above picture: Innocent looking enough, but Marion Island’s House Mice are a threat to the island’s seabirds that must be addressed; photograph by Stefan Schoombie
From time to time, the Mouse-Free Marion (MFM) Project receives queries, often via social media (such as on its Facebook page), as to why attempts are not being made to reduce predatory attacks by House Mice on the island’s seabirds, prior to the planned eradication attempt in 2025. A regular suggestion received is to deploy mouse traps on or around breeding colonies or individual nests of albatrosses and other seabirds. For example, a recent query from a project supporter, referring to the recent observation of a Wandering Albatross Diomedea exulans chick that succumbed to a mouse attack, stated in part “with so many intelligent and very simple mouse traps that could have been deployed around the most sensitive breeding colonies a small dent could be made and could even have saved one Wandering Albatross chick.”
A Wandering Albatross chick on Marion Island recently attacked by mice died from its wounds soon thereafter (click here); photograph by Michelle Risi
This a sensible question to ask and requires a detailed response setting out why the MFM Project is directing all its efforts at a once-off eradication and is therefore not also attempting to intervene beforehand by controlling mice to save the lives of individual birds.
MFM Operations Manager, Keith Springer, a veteran of successful rodent eradications on the sub-Antarctic islands of Antipodes, Macquarie (which he led) and South Georgia, comments “It’s very rare in eradication operations to undertake pre-emptive control measures, although the suggestion is often raised by concerned stakeholders. Apart from anything else, the effort has to be maintained over the long term, because trapped mice are quickly replaced by newcomers taking over vacant territories, so you can’t just trap and leave. But it is usually the requisite logistics that preclude this sort of work on any meaningful scale.”
Marion is a large island – 30 000 ha in size with a coastline of some 100 km. Seabirds at risk of mouse predation breed all around the lowlands of the island, up to, and in some cases, above the upper vegetation line at 400 m above sea level. For all but a couple of weeks in April/May – during the annual relief when a helicopter might be available for a few field flights – getting around the island is all done on foot. These excursions make for challenging walking. Taking Wandering Albatrosses as one example, hundreds of breeding birds are scattered over the coastal lowlands, with nests usually tens of, or a hundred or more, metres apart. Some nests on the west coast will require two to three days of hard walking just to reach them! Not all albatross colonies are close to the existing field huts. A stipulated safety requirement for field staff on the island is to travel in pairs at a minimum.
So, trapping around Wanderer nests would not be an easy task, especially as traps – of any design – would ideally need to be checked on a 24-hour basis to remove dead mice and reset them throughout the whole of the months-long breeding season. Bait will often be scavenged by birds, eaten by invertebrates, or simply washed away by rain, thus requiring regular replacement. As Keith says, “scaled to the number of susceptible individuals it would be a massive logistical undertaking”. Crucially, it would require a diversion of funds currently being raised to allow the eradication to go ahead, and thus make the fund-raising target significantly higher. This would likely further delay the eradication operation while the additional funds are raised. The project would also need to submit a proposal to the authorities to undertake a control programme, that will also require ethical approval.
Many Grey-headed Albatross nests on Marion Island will need ropes to access safely; photograph by John Dickens, poster design by Michelle Risi
It is granted that with the necessary go-ahead, a single field worker might be able to employ and service daily (in all weathers) half a dozen or so mouse traps around each of the handful of Wandering Albatross nests to be found with a few hundred metres of the meteorological station for a full year. But we will not know in advance which of these nests might be attacked by mice (not all will be), so the considerable amount of work required at even this low level might be in vain. Applied across the whole island, we would need to have a protective trap network around every Wanderer nest to intercept the mice that will attack individual nests, which we cannot anticipate.
Considering another species known to be seriously affected by mice, the Grey-headed Albatross Thalassarche chrysostoma, the difficulties appear close to insurmountable. A full day’s strenuous walk from the meteorological station (not safe to undertake on really bad weather days), a minimum of two field workers would need to spend a whole summer living in the nearby field hut. Because many of the nests are located on steep cliffs, they would need to be qualified and experienced rope-acess technicians to access in safety many of the nests to set and service traps, with no chance of immediate rescue if an accident occurred. Rope work is very time-consuming to set up, thus the team would only be able to service a tiny proportion of the thousands of nests on the required daily basis. Getting approval for this, with necessary (and hugely expensive) insurance in case of the need for a medical evacuation back to mainland South Africa, would be problematic at the very least!
To undertake control work at the scale required to have a conservation value for any of the affected albatross species would require a large number of staff deployed to the island and likely the placement and upkeep of new field huts to allow mice to be trapped around more than a handful of nests. Including some of those of the badly affected burrowing petrels (such as the winter-breeding Grey Petrel Procellaria cinerea) would make the effort even more expensive and they would come up against the limited accommodation facilities in the supply ship and on the island alike.
A Grey Petrel chick at risk to mice on Marion Island; watercolour by Coleen Laird after a photograph by Michelle Risi courtesy of the Agreement on the Conservation of Albatrosses and Petrels
The MFM Project’s goal is to conserve the island’s seabird populations and help its ecological restoration by eliminating the introduced mice population entirely. Saving the lives of some individual birds by a limited control operation over the next two years will unfortunately have no meaningful conservation value, will be very expensive, and can only detract from the hard, largely behind the scenes, planning work that is currently keeping the MFM Project Team fully occupied up to seven days a week.
The concern expressed about individual birds, such as Wandering Albatrosses, continuing to be killed by mice is completely understandable, as is the desire for something to be done about it now. The photographs coming back from the island of wounded and dead birds are distressing to everyone who sees them. The project team deeply regrets and is further motivated by the death of every single attacked bird on the island but must continue to devote all its efforts and finite resources to the main prize, the end of all of Marion Island’s mice during a single eradication operation.
John Cooper, News Correspondent, Mouse-Free Marion Project, 18 July 2023
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A Wandering Albatross broods its chick – both are at risk to mice; photograph 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.
