Rats gone: Tenfold increase in wedge-tailed shearwaters on 2 Seychelles' islands
The population of wedge-tailed shearwaters on D'Arros Island and St Joseph Atoll in Seychelles has increased tenfold, according to the Save our Seas Foundation (SOSF), which highlighted a successful eradication of rats, in a paper earlier this year for the Marine Ornithology journal.
The project to eradicate rats was undertaken in the year 2003 and the island was declared rat-free in 2005.
This statement is supported by a series of surveys and research papers on the birds. The original survey was done in 2009 by scientists led by Michelle Kappes, the 2017 survey was conducted by Danielle Keys, and the 2021 survey was by current D'Arros research centre staff.
Invasive rats and mice inhabit 80 percent of the islands in the Indian Ocean region and pose a serious conservation threat to breeding seabirds. Rodents easily prey on eggs and chicks of nest-bound birds and, in some cases, even brooding adult seabirds, which have not developed any sense of anti-predator behaviour.
«The result, as seen on Marion Island, is that seabirds face local extinction. Without successful intervention on this sub-Antarctic island, scientists believe that 19 out of 28 bird species could be lost by 2030,» said the Save Our Seas Foundation D'Arros Research Centre.
The population of wedge-tailed shearwaters on D'Arros Island and St Joseph Atoll in Seychelles has increased tenfold. (Save Our Seas Foundation, Rainer von Brandis) Photo License: All Rights Reserved
According to the chief executive of SOSF, James Lea, this latest study estimated 2,768 and 2,406 breeding pairs in 2016 and 2021, respectively, nearly 10 times larger than estimated in 2009.
«D'Arros has preventive measures in place to ensure that the biosecurity of goods transported to D'Arros is implemented at source, and in addition, they have pens at offload sites and traps set around the island that provide a second layer of security,» said Lea.
Danielle Keys, a researcher from Nelson Mandela University in South Africa, said, «The shearwaters on D'Arros island make up the largest breeding population in the western Indian Ocean compared to Madagascar, Mauritius, and the Comoros. St.Joseph Atoll is one of the largest breeding colonies of wedge-tailed shearwaters in the western Indian Ocean and Fouquet Island is home to most of them.»
The researcher stated that St. Joseph Atoll represents as much as 16 percent of the total population of wedge-tailed shearwaters in the western Indian Ocean. As a result, these birds might also be repopulating D'Arros Island, which lies two kilometres from the St Joseph Atoll, as birds find new nesting grounds nearby to avoid overcrowding on the atoll. Scientists call this phenomenon a 'source population.'
Understanding the changes enables researchers and managers to prioritise the future and perhaps even look to safeguarding populations elsewhere.
The Save Our Seas Foundation said that given the importance of the area to these breeding seabirds, the long-term monitoring of wedge-tailed shearwaters can help guide researchers on conservation strategies.
At present D'Arros Island, which is a private island, is occupied by staff of the Save Our Seas Foundation D'Arros Research Centre and they continue to monitor the shearwater population and promote its conservation as part of their long-term monitoring programmes.
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