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The battle of birds and mice

Not many South Africans know that our country has overseas possessions. They are Marion and Prince Edward Islands in the Southern Ocean, 2 200km south-east of Cape Town. Completely uninhabited – save for a weather and research station on the larger Marion Island – the two sub-Antarctic islands are cold, windy, wet and inhospitable to humans. In marked contrast they are home to millions of seabirds and seals. Among this teeming life are thousands of albatrosses, some of which may be seen on birding tours out of Cape Town. John Cooper and Robyn Adams, of the Mouse-Free Marion Project, write about the islands’ albatrosses and the threats they face on Marion from diminutive House Mice.

Five species of albatrosses breed on Marion and Prince Edward Islands. The largest, with a wingspan of up to 3.5m, is the Wandering Albatross, iconic in life and literature. With nearly half the global population, South Africa is a stronghold for this threatened species. The Grey-headed Albatross is the most abundant on Marion, with approximately 9 500 annually breeding pairs for both islands combined, breeding in colonies on coastal and inland cliffs – unlike the approximately 3 650 annually breeding pairs of Wanderers that space themselves out to breed on low-lying boggy ground near the coast.

Two closely related species are the Sooty (3 500 pairs) and Light-mantled (500 pairs) Albatrosses; chocolate-coloured birds that are consummate flyers, often as pairs in unison along the coastal cliffs where they breed in loose colonies. The fifth, and smallest, is the Indian Yellow-nosed Albatross, of which an estimated 7 000 pairs breed on Prince Edward Island in mixed colonies with Grey-headed Albatrosses on steep vegetated slopes facing north-east, seeming to offer a more equable climate than does Marion.

Prince Edward Island has always been free of introduced predators, but Marion has not been as lucky. House Mice were inadvertently introduced by sealers around the beginning of the 19th century and rapidly spread over the whole island. A few domestic cats were deliberately taken to the island in 1948, soon after South Africa annexed the islands and established the weather station, to control the mice that had invaded the buildings. Their offspring became feral, living off an estimated 450 000 small burrowing seabirds a year. A long campaign finally removed all the cats in 1991. However, the mice remained and in the absence of cats (and in a warming and drying environment thought to be due to climate change) their numbers have increased, and likely as a consequence they have taken to attacking albatross chicks of all four of the species that breed on Marion Island. Scalping attacks take place at night, mainly during the winter months when the usual mouse diet of grass seeds and invertebrates is scarce. The chicks eventually succumb to loss of blood – a grisly way to go.

The Mouse-Free Marion Project is working towards eradicating the albatross-killing House Mice by aerial dispersal of rodenticide bait from helicopters. The eradication will take place during winter when most seabirds have left the island. Upon successful completion the project will have restored the breeding habitat of over two million seabirds, many threatened, and improved the island’s resilience to a warming climate.

The Agreement on the Conservation of Albatrosses and Petrels

The Agreement on the Conservation of Albatrosses and Petrels (ACAP, www.acap.aq), of which South Africa is a founding member, is an inter-governmental organisation that works to conserve albatrosses and petrels by coordinating international activities to mitigate threats to their populations. In 2019 ACAP declared that a conservation crisis continues to be faced, with thousands of albatrosses dying every year as a result of fisheries operations and from rodents, cats and pigs introduced to many of their breeding islands. To increase awareness of this crisis ACAP inaugurated a World Albatross Day (WAD), to be held annually on 19 June. The theme for WAD2023 is Plastic Pollution, to highlight the threats albatrosses face from ingesting plastic objects that they mistake for prey at sea.

Want to spot an Albatross?

Tourist landings on Marion Island, a Special Nature Reserve, are not permitted and cruise ships very rarely go that way. A sub-Antarctic cruise elsewhere can be prohibitively expensive. So how do ordinary South African bird watchers get to see albatrosses for their life lists? Don’t worry, there is a way!

Regular guided day trips, known as ‘pelagics’, on small vessels are made from the Cape Peninsula. The boats look for a trawler with its net down, and close-up views of the often attending albatrosses and petrels from the Southern Ocean allow for ‘lifers’ and excellent photo opportunities for those with long lenses. Up to half a dozen species of albatrosses can be seen, expertly pointed out by the guides, with the Black-browed Albatross being the most abundant.

*For more information: https://www.zestforbirds.co.za/ and https://www.capetownpelagics.com/. Less regular trips take place out of Durban and the Eastern Cape. Search for them online.

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