Picture: Reuters.
Johannesburg - If it all goes right it will end the reign of an unlikely killer, but if it goes wrong several species will disappear from this corner of the far southern Indian ocean.
The killer is not much bigger than a match box but on Marion island they are predators that prey on sea birds hundreds of times their size. This after it was discovered that these birds are defenceless against their attacks. The culprit is the house mouse which was introduced to the island in the early 19th century, most likely by visiting sealers.
The problem is that over the last three decades conditions on Marion have become warmer and drier which, scientists believe, have caused a bloom in the mice population. With more mice on the island, the rodent species experiences extreme food scarcity in winter forcing them to turn to their new prey.
The mice have learnt to attack bird chicks and even the adults. Over the last couple of years the frequency of these attacks has increased and the fear is that this could force 19 out of the 28 species found on Marion island to become locally extinct in the next couple of decades.
One of these birds is the Wandering Albatross with its 3,5 metre long wingspan. A quarter of this bird’s population is found on Marion island.
To save these bird species and the ecology of Marion island an ambitious rodent eradication programme is under way.
The plan is to kill every house mouse on the 30 000 hectare island. If all goes to plan Marion island will be mouse free by the end of the winter of 2025.
“You know 50 years ago, people wouldn't have considered it possible to eradicate rodents from an island the size of Marion and with the topographical complexity of the island,” says Dr Anton Wolfaardt the Mouse-Free Marion Project Manager.
“But you know, increasingly larger and more complex islands are being tackled and rodents have been successfully eradicated. So this kind of paved the way for an operation like ours.”
The programme involves BirdLife South Africa and the department of forestry, fisheries and the environment and it will be a costly exercise, with an estimated price of R460 million. Funds are still being raised.
The reason for the huge expense is the logistics of getting a fleet of helicopters and their crews down to the island that lies about 2200 kilometres from Cape Town. Helicopters will drop rodenticide across the island in a once off operation.
Mark Anderson, the CEO of Birdlife South Africa believes this would be a massive conservation gain for the Southern Ocean’s bird population.
“The Mouse-Free Marion Project is by far the largest, as well as the most important, conservation project that BirdLife South Africa has ever undertaken,” he says.
Currently the organisers are in the planning phase of the operation. If all goes to plan the rodenticide will be dropped between April and August. It will be done in winter when the birds are out at sea and when there will be less food around for the mice, making them more likely to eat the poison. The rodenticide is expected to have little effect on the local bird population, as most species feed on fish. The team will only know if they have been successful about two years after the operation.
Then dogs trained to sniff out rodents and scientists will scour the island looking for signs of mice.
“Many of these sea birds face other pressures and threats, such as those linked to climate change, and the removal of the mice will make them more resilient in facing other pressures,” says Wolfaardt.
It is a daunting endeavour but South Africa has been here before. In the 1970s Marion island had another alien problem. In the late 1940s five cats were introduced to help clear out the mice that had taken up residence in the buildings on the island. The population of five cats grew to 2000 and it was estimated they were killing half a million birds a year. The last cat was killed in 1991, making it the most successful cat eradication programme on such a large island.
“So in many respects we are hoping to follow their example,” says Wolfaardt.
Related Topics: