A project aimed at removing invasive rodents from two small islands in the Isles of Scilly started in 2013. The effort focused on St Agnes and Gugh after brown rats were identified as a serious risk to local seabird populations that nest there. Following the completion of the work the islands have stayed free of these rodents. This change has allowed breeding activity among Manx shearwaters to grow substantially. Before the initiative began surveys showed only 22 pairs of these birds. By 2025 the count of apparently occupied breeding sites reached 225.
The removal operation addressed a long standing threat to nesting seabirds on the islands. Brown rats had been present and were known to prey on eggs and young birds reducing the chances for successful reproduction. Once the islands were cleared of rats the seabird colonies gained a safer environment for raising offspring. The increase in recorded sites indicates that more pairs are now able to establish and maintain nests without interference.
Over the twelve years since the project ended ongoing monitoring has confirmed that the islands remain rodent free. This sustained condition has supported steady growth in the shearwater population. The jump from 22 pairs to 225 sites represents a clear recovery in breeding activity. Such results highlight how targeted removal of invasive species can lead to measurable improvements in local wildlife numbers.
The islands of St Agnes and Gugh provide important habitat for seabirds that return each year to breed. Manx shearwaters in particular rely on secure nesting locations free from predators. The success of the 2013 effort has created better conditions for these birds to thrive. Continued observation through 2025 shows the positive effects persisting over more than a decade.
Overall the project demonstrates the value of addressing invasive species in sensitive island ecosystems. By eliminating the rats the breeding success of shearwaters has risen markedly. The recorded growth from a small number of pairs to a much larger count of sites offers evidence of recovery. This outcome has been tracked consistently since the initial operation and remains stable today.
