Tristan Albatross breeding success is too low
The life of an albatross chick between the time when it hatches from the egg until it can eventually fly away isn't particularly glorious. Hunkered down between wet grass on windswept islands in the southern oceans these chicks have to wait for their feathers to grow. They have to endure gale-force winds and driving rain, hail, and snow - and wait. Not for a few days or weeks, but roughly for 8-9 months. Some chicks do not survive that long.
A 5-month old Tristan Albatross chick begging for food (S.Oppel)
The inclement weather, however, isn't the main culprit for the loss of Tristan albatross chicks on Gough Island in the South Atlantic. Mice that were introduced by sailors have gradually learned to eat albatross chicks that are unable to fly or run away. Every year, hundreds of albatross chicks are eaten alive by mice.
The count of albatross breeding pairs and chicks
Finding out just how many chicks survive every year is a key task of the RSPB team on Gough Island. Twice each year, in January and September, the team hikes around the island and counts all Tristan albatrosses. In January adult birds are incubating eggs, and in September large chicks are counted to provide data on the year's success rate.
RSPB team hiking around Gough to count albatrosses (S.Oppel)
Breeding success on Gough is much lower than elsewhere.
On islands without invasive species, large albatrosses generally manage to raise ~60-70 chicks for every 100 breeding pairs. On Gough, however, the number of chicks that fledge out of 100 breeding pairs is significantly lower – on average only around 30-40. And this figure may even be too optimistic: the large chicks are typically counted in late September, but the young albatrosses fledge only in November, so chicks that are counted in September may still be killed by mice.
In last years’ counts only 309 chicks survived from 1453 nests – just 21%. And this is fairly typical, the Tristan albatross breeding success has suffered year after year because of the presence of invasive non-native mice. The graph below shows the breeding success of Tristan albatross since 2001. The blue line shows the average success on Gough where invasive mice are present, whilst the red line shows the average breeding success of comparable albatross species on predator-free islands. Even in the best years on Gough the albatrosses do not raise enough chicks, and the difference highlights the impact mice have on Gough's seabirds.
The breeding success of Tristan Albatrosses on Gough Island between 2001 and 2018 based on counts of incubating pairs and large chicks. Breeding success is the percentage of pairs where a large chick survives until September. The blue line is the long-term average on Gough, the red line is the typical average for other large albatrosses from islands without invasive species.
This poor breeding success is unsustainable. The Tristan albatross is Critically Endangered, and it is likely that without action this species will go extinct within a few decades.
The Tristan albatross is not the only species affected by mice. Fifteen of Gough's bird species are negatively affected by invasive mice. Smaller species, such as storm petrels or McGillivray's prions, may lose virtually all their chicks every year to mice.
However, there is hope for the albatross and other birds! The Gough Island Restoration Programme is a major conservation action, which, if successful, will remove the threat of mice from Gough Island allowing populations of Tristan albatross to recover on a predator-free island.
You can support the restoration of Gough Island by sharing this blog or donating directly to the project via the website.
The Gough Island Restoration Programme is being carried out by the RSPB in partnership with Tristan da Cunha , BirdLife South Africa and the Department of Environmental Affairs in South Africa and Island Conservation . The programme is part-funded by the RSPB, the UK Government, the National Fish and Wildlife Foundation and other generous individuals and organisations.