Monitoring teams on the sub-Antarctic islands of Gough and Marion observed for the first time that introduced house mice inflict severe wounds on adult Tristan and wandering albatrosses, which can lead to the death of the large seabirds.
Until now, it was only known that albatross chicks fall victim to house mice (Mus musculus). However, in a study recently published in the journal Biological Invasions, a team of scientists from South Africa and the United Kingdom report on adult albatrosses that were attacked by mice during breeding.
In March and April 2021, the team observed three adult Tristan albatrosses (Diomedea dabbenena) with wounds typical of attacks by mice for the first time on Gough Island in the South Atlantic as part of regular monitoring. Two of the albatrosses probably abandoned their nests and the third was found dead days later.
On Marion Island south of South Africa in the Indian Ocean, the team encountered a similar situation in April 2023. Here they found two injured and eight dead wandering albatrosses (Diomedea exulans).
The mice, which were most likely unintentionally introduced to the islands by sealers and seafarers in the early 19th century, have proliferated over the last 30 years, not least due to climate change. The invertebrates that the mice actually feed on have been decimated to such an extent that they have had to look for alternative food sources. They found easy prey in seabirds and their chicks, which do not fight back. The inconspicuous rodents attack healthy birds and inflict serious wounds, usually to the head, elbows and back, which often lead to death.
The first reports of suspected mouse attacks on seabirds date back to the 1970s from the Farallon Islands off the coast of California. On the two sub-Antarctic islands, mouse attacks on seabird chicks have been observed for 20 years. However, according to the team of authors, the attacking of breeding adult birds is a new phenomenon. The unusual behaviour of the mice was first documented in the Southern Ocean in 2017 on an adult breeding Northern Giant Petrel (Macronectes halli) on Marion Island. It recovered from its injuries. On Gough Island, which is part of the Tristan da Cunha archipelago, an adult Tristan albatross with wounds from mice was sighted for the first time in March 2018. This bird also recovered and bred successfully.
Breeding colonies of global importance
Both islands are considered biodiversity hotspots: numerous species of seabirds – 24 species on Gough Island and 28 on Marion Island – use the two islands as their breeding grounds, including penguins, other albatross species and various species of petrels.
For the critically endangered Tristan albatrosses, which are only slightly smaller than wandering albatrosses, the mice pose a major threat. Gough Island is home to practically the entire breeding population of Tristan albatrosses with 1250 to 1750 pairs.
And Marion Island is one of the most important locations for the vulnerable wandering albatross – with around 2300 pairs, 24 percent of the global breeding population breeds here.
The large albatrosses are particularly sensitive to threats such as attacks by mice, as they reproduce very slowly. They only breed for the first time from the age of 11 to 15 years and, if successful, only every two years. They therefore have little to offer against mice, which produce several generations every year.
The difficulty of clearing the islands of mice
The only way to protect the albatrosses and other seabirds from attacks by the 20 gram rodents and the associated population decline is to eradicate the mice.
In 2021, great efforts were made to eradicate the mice on Gough Island using poisoned bait. But just six months later, mice were spotted again. Although the eradication programme was unsuccessful, the Royal Society for the Protection of Birds (RSPB), which is involved in the current study, was nevertheless able to report important successes: The breeding success of Tristan albatrosses last year was over 75 per cent with 1,186 chicks from 1,570 breeding pairs, according to the RSPB. In the previous 20 years, only around 30 per cent of breeding pairs were successful on average. The other seabird species have also increased significantly. The Gough Island Restoration Programme continues to pursue the goal of eradicating mice from the island.
In order to protect the wandering albatrosses and the numerous other species on Marion Island, an eradication programme, the Mouse-free Marion Project, is currently being planned, which is to be implemented in winter 2026 if funding can be secured. The project is a partnership between the South African Department of Forestry, Fisheries and Environment and BirdLife South Africa.
The planning and implementation of eradication programmes are extremely time-consuming and costly, especially on remote islands in the middle of the ocean. As on Gough Island, poison baits are to be deployed over the entire island of Marion Island using helicopters. Not an easy endeavour, but in the past this method has successfully eradicated rodents on large islands, e.g. on South Georgia.
In order for the Mouse-free Marion Project to actually be implemented, funding for the programme must be secured. The project team has already been able to win over important partners, but still needs more support.
We at PolarJournal are very concerned about restoring the ecological balance on Marion Island and protecting the sub-Antarctic birdlife. We are therefore supporting the project with a donation.
Julia Hager, PolarJournal
Featured image: Heiner Kubny
Link to the study Connan, M., Jones, C.W., Risi, M.M., Smyth, L.K., Oppel, S., Perold, V., Stevens, K.L., Daling, R. & Ryan, P.G. 2023. First evidence of mouse predation killing adult great albatrosses. Biological Invasions doi.org/10.1007/s10530-023-03177-2
More information about Gough Island: https://www.goughisland.com/
More information about Marion Island: https://mousefreemarion.org
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