A project to protect breeding seabirds from invasive rats on the Scilly Isles has been a success with the two islands declared “rat-free”.

Bird populations on St Agnes and Gugh, linked by a sand bar, are starting to recover after a quarter century of year-on-year declines following work to eradicate the non-native brown rats which were feeding on eggs and chicks, conservationists said.

They are thought to have first colonised the islands in the 18th century following several shipwrecks and grew to a population that was harmful to birds such as European storm-petrels (Hydrobates pelagicus) and Manx shearwaters (Puffinus puffinus), which have been in decline since the 1980s.

Local volunteers and conservationists began work in 2013 on a project to monitor rat activity on the island, followed by an intensive programme of baiting and poisoning for a month in the winter. No rats have been spotted since November 2013, and after a thorough month-long inspection at the beginning of this year the islands have been declared officially “rat-free”.

Since the removal of the rats, both Manx shearwaters and European storm-petrels are successfully breeding on the islands for the first time in living memory, conservationists said, with more than 40 chicks recorded on the islands in the last two years.

Storm-petrel (Hydrobates pelagicus) population is also expected to recover after years of decline. Photograph: Rick Price/Getty Images

Jaclyn Pearson from the RSPB, who manages the project, said: “Getting to this stage is a fantastic achievement and everyone involved is delighted that the islands are now officially rat-free.

“This, and the recovery of the seabirds so early on, is testament to the hard work of the team and the 100% support from the local community.”

Sarah Mason, chief executive of Isles of Scilly Wildlife Trust, which looks after most of the land on which the birds breed, said the news was fantastic for the islands’ bird life. “The Trust’s land management work is now more important than ever; we must ensure that habitats across the islands are suitable for our iconic seabirds so that they can be enjoyed by future generations,” she said.

Local Richard McCarthy said: “St Agnes and Gugh are very special places. When I first learned that our community was being selected for this project, I was only too pleased to encourage fellow islanders to back rat removal.

“The speed with which this was achieved and seabird recovery began has surprised us all. Young and old, we must now do our level best to ensure that as far as possible we minimise the likelihood of rats returning.”

