"A project aimed at protecting internationally important seabird populations on two of the Isles of Scilly by killing more than 3,000 brown rats, is under way.
Eradication experts from New Zealand and the UK have been contracted to carry out the work.
"Among many challenges our seabirds face, the greatest threat on land is predation of eggs and chicks by brown rats," said Jaclyn Pearson from the Isles of Scilly Seabird Recovery Project.
"The brown rats were accidently introduced to islands from shipwrecks in the 18th Century," she added.
The project is part of a 25-year programme to protect "internationally important" seabird numbers, including those of Manx shearwaters and storm petrels, and is costing more than £755,000.
Tony Whitehead, from the RSPB, said: "Eight out of ten islands around the world now have rats, including remote places such as Tristan da Cunha in the South Atlantic and Henderson Island in the South Pacific.
"The predators are known to have impacted on the populations of 75 species of seabird, from albatross to shearwaters to small petrels.
"In response, there is a worldwide effort to rid islands of these voracious creatures," he added.
In January, Richard Bellamy, head of the Heritage Lottery Fund (HLF) South West, said we have a "collective responsibility for the native wildlife on the Isles of Scilly".
HLF has awarded the project £269,100, alongside £460,255 from the EU Life fund, with further contributions from Isles of Scilly Area of Outstanding Beauty Sustainable Development Fund and Natural England."