SA choppers fight bird-eating mice
● It’s a liberation struggle few have heard about — and South Africans are helping to win it.
Seabird-eating mice on Gough Island in the South Atlantic should soon be on the retreat thanks partly to helicopters from Johannesburg and SA’s hi-tech research ship, the SA Agulhas II.
Local technicians and scientists are also involved in an international effort to combat a house mice menace threatening one of the world’s prime seabird nesting sites.
The Gough Island Restoration Programme, led by the Royal Society for the Protection of Birds (RSPB) on behalf of Tristan da Cunha, celebrated a landmark this month with the completion of the successful mouse-baiting phase.
For the past three months, helicopter pilots have battled fierce winds and mountainous terrain to bombard Gough Island with poison pellets. In this way the team is hoping to stop mice preying on seabirds, at the rate of about 2-million a year.
With all the bait now distributed, the team will only be certain they have succeeded in the autumn of 2023. Early indications suggest the bait may be working.
Gough forms part of the British-governed Tristan da Cunha archipelago, considered the most remote inhabited archipelago in the world.
Mice arrived more than a century ago by jumping ship when sailing vessels called, and the first evidence of mice eating birds goes back 20 years. Researchers say the birds are particularly vulnerable to mice predation — which occurs mostly in winter when other food sources for mice are scarce — because they have not had time to evolve a defence mechanism.
“The first evidence we had of mice eating the birds was in the 2000/2001 breeding season of Tristan albatrosses,” said RSPB spokesperson Anna Feeney.
“It’s possible that the mice ate the eggs and potentially chicks of smaller burrow-nesting birds quite soon after their arrival on the island, but these birds are enigmatic species and hard to study so this is likely to have gone unnoticed until the injuries were seen on the surface-nesting species. We followed up with burrow cameras to confirm the underground picture,” she said.
Pictures and film footage confirmed that the mice feed on birds many times their own body size, in some cases inflicting mortal injuries.
The restoration team has used a “rodenticide” that biodegrades and does not leach into watercourses. Feeney said a similar strategy is planned for SA’s own Marion Island in the sub-Antarctic Indian Ocean, where mice are also targeting seabirds.
“The [Marion] operation will also launch out of Cape Town, like Gough, so there’s much knowledge to be shared between the two projects,” she said.
Justin Pienaar, chief operations manager of Aeronautical Solutions, said the Midrand company had supplied four helicopters to carry out the Gough baiting programme. He said saving seabirds was an unusual deployment, although the company was geared for specialised work.
The helicopters had to be shipped 2,700km to the island aboard the SA Agulhas II. It took two days to sling the backup equipment onto the island using cargo nets.
Flying conditions were challenging due to the winter weather and steep terrain, Pienaar said. “The weather is very unpredictable. That makes it a bit difficult for the pilots. But they finished ahead of schedule.”
In a newsletter about the restoration operation, RSPB programme manager Helen Deavin paid tribute to the international baiting effort. “We are so grateful to all the many people who have got us to this point in the project. The mission to restore Gough Island would have been impossible without a strong partnership,” Deavin said.