One of the world’s rarest birds, the Wilkins’ Bunting, was facing extinction with its food source under threat. We look at how a tiny wasp has handed the bird a lifeline, and the epic 10,000km journey that’s made this possible.
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The Wilkins’ Bunting is a delicate, fruit-eating finch found only on the remote Nightingale Island in the British Overseas Territory of Tristan da Cunha in the South Atlantic Ocean.
Much like Darwin’s famed finches of the Galapagos, birds across the islands of Tristan da Cunha have similarly evolved into separate species with distinct niches. The Wilkins’ Bunting has evolved to specialise on the fruits of Tristan’s only native tree, Phylica arborea, using its large, powerful bill to crack the fruits open to get to the seeds inside.
However, the accidental introduction of an invasive scale insect has devastated the Phylica trees that the birds depend on. The insects infest the trees and by secreting honeydew, they encourage the growth of a sooty mould which can completely smother and kill the trees.
In 2019 two major storms hit the island. With the trees already weakened by the insects, an estimated 80% of the island’s forest was lost during these weather events. Already critically endangered, the future for Wikins’ Buntings looked bleak. Urgent action was needed to prevent the first global bird extinction on British soil for over 60 years.
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A group including the RSPB, CABI, FERA and the Tristan da Cunha Government came together and developed a plan to save the buntings. This was to target the invasive scale insect, set up a tree nursery to boost the number of fruiting trees. and improve island biosecurity to avoid similar occurrences in future.
In 2020, entomologists set out to try and find a way to deal with the scale insects. A break-through came when a small parasitoid wasp Microterys nietneri was found to be successful in controlling the scale insect, without having any adverse impacts on other species.
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But the crucial next step meant getting the wasps to the island, a journey of more than 10,000km whilst Covid restrictions were still in place.
Dr Norbert Maczey, an entomologist at CABI recalls: “The wasps faced an epic journey. Firstly, a flight from London to Cape Town, in a cool bag followed by an enforced stay in a hotel room as part of a staff member’s Covid quarantine.
“Next came a week-long boat journey to Tristan with temperatures sometimes dropping below zero. Finally, there was a further boat trip to Nightingale Island. It seemed like luck and time was against us but some of the wasps made it.”
Less than 10% of the wasps survived the journey of almost a month by land, sea and air. But thankfully, it proved enough, and the first release of wasps on Nightingale Island took place in April 2021. This was followed by additional releases over the next two years and eventually a population of wasps started to establish itself.
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Dr Maczey explains: “Despite the weather on Tristan frequently being cold, wet and windy, the wasps established surprisingly quickly, parasitism rates of the scale insects are currently high, and the trees are already showing signs of recovery.”
With the trees now recovering, the future is looking brighter for Wilkins’ Buntings. Tree numbers have also been bolstered by the establishment of a Phylica nursery, providing healthy trees to reforest the islands.
In February 2024, a survey estimated there to be between 60 and 90 breeding pairs of Wilkins’ Buntings. While the birds remain at risk, the tiny wasp is now controlling the damaging scale insect, and we are confident that numbers of buntings should stabilise and will have a chance to recover over the next few years.
As David Kinchin-Smith, the RSPB’s UK Overseas Territories Project Manager explains: “This project shows what can be achieved in turning around the fate of a threatened species. Steely determination, ecological expertise and a large helping of luck have all contributed to the success of this work, but hopefully we, and the wasps, have given the buntings a much-needed lifeline.”
Funding for the project ‘Saving Tristan’s only native tree and its associated unique buntings’ was provided by the Darwin Plus, UK Government grant scheme, and the John Ellerman Foundation. Thank you!
