Scientist flags mice menace in sub-Antarctic
A Nelson Mandela University researcher has highlighted the threat to a vulnerable albatross population on a South African sub-Antarctic island as a result of attacks by alien house mice.
Dr Maelle Connan is the lead author of a recent report on the first evidence of mice killing adult wandering albatross on Marion Island.
Connan said scientists had known for 20 years that mice were attacking the chicks of adult wandering albatross on Marion and Tristan albatross across on Gough Island, also in the sub-Antarctic.
But the evidence that the mice are now going for breeding adult great albatross poses a grave new threat.
“It emphasises the urgent need to eradicate introduced mice from these islands.”
She said scientists on Marion Island had discovered the situation in April last year.
“Carcasses of eight adult wandering albatross were found within a 6ha area around where [three] wounded birds had been found.
“The two carcasses that were relatively fresh; both showed signs of mouse-inflicted wounds on the elbows of the wings.
“The other six were too decomposed to detect wounds.
“These were the first reported deaths of adult great albatross resulting from house mice. The primary cause of death is unknown but two hypotheses exist — the wounds prevented the birds from flying, or the birds succumbed to secondary infection.”
Wandering albatross are listed as vulnerable on the International Union for Conservation of Nature red list.
“Of the 10,000 breeding pairs left globally, about 3,000 are found on Marion Island.
“This shows the importance of removing mice from the island to protect the native species and whole ecosystem.”
Connan said the mice arrived on Marion and Gough islands on vessels used by sealers in the early 19th century.
Without predators and with plenty of food, they thrived, dramatically changing the vegetation and attacking the birds.
She said environmental changes had caused mice to breed earlier each summer on Marion Island.
“This has resulted in higher mouse densities in late summer and a reduction in the availability of their main food of invertebrates and plant seeds.
“Mice are forced to search for alternative food sources, initially attacking the more vulnerable seabird chicks and now breeding adults.”
She said long-term monitoring of the breeding success of wandering albatross on Marion Island indicated a slow decline over the past 15 years.
She said an attempt in 2021 to eradicate mice from SA’s Gough Island had been unsuccessful.
However, the goal had been achieved on New Zealand’s Antipodes Island, proving that it was possible and site-specific research was needed to develop strategies that would work.
“Working together with the Department of Forestry Fisheries and Environment, the Mouse-Free Marion team is aiming to do a poisoned bait drop on Marion in 2027, should funding be secured.”
She said the poison bait method was the only one with a proven track record in eradicating mice for an island the size of Marion, and also considering the difficult weather conditions.
“The sooner mice are removed from these fragile island ecosystems, the sooner they will recover.”
She said though Marion Island was far away from mainland SA, it was a valuable asset.
“South Africans should really be proud of Marion and the rest of the Prince Edward Island group, of the research of international calibre that is being conducted there, and of the efforts by the [department] to protect and preserve the islands and their environment for future generations.”
Connan said they would be taking care to avoid secondary poisoning.