Background The Isles of Scilly lie at the centre of a large network of Natura 2000 sites covering 26 851 ha. The archipelago is home to the following habitats and species: sandbanks that are slightly covered by seawater all of the time; mudflats and sandflats not covered by seawater at low tide reefs; shore dock (Rumex rupestris), grey seal (Halichoerus grypus) and the project’s main target bird species, the storm petrel (Hydrobates pelagicus) and Manx shearwater (Puffinus puffinus). In addition, the Isles of Scilly contains SSSIs of national importance for vascular plant species, vascular plant associations, breeding shorebirds and lichens. Project actions will take place mainly on the islands of St Agnes and Gugh in the southern part of the Scilly SPA. These are two separate islands that are connected by a rock and sand bar at low tide. St Agnes (105 ha) has cultivated farmland at its centre, surrounded by heathland, maritime heath, a few wooded areas and sandy and rocky shores. Gugh (37 ha) has regenerating heathland, maritime heath, marram dunes, a small wooded area and a rocky shoreline. The brown rat (Rattus norvegicus) is widespread and abundant on both islands, and was probably introduced as a result of shipwrecks in the 18th century. The presence of brown rats (estimated at 3 300 individuals) is responsible for the loss of adults, young and eggs of both the main target bird species within the Isles of Scilly site, and is therefore affecting the population sizes and distributions of these species. Objectives The overall purpose of the project is to maintain and enhance the conservation value of the Isles of Scilly Natura 2000 network site by removing brown rats from two key islands within this SPA. The main target species, the storm petrel and the Manx shearwater, are a key component of the internationally important seabird assemblage. The project is also likely to benefit other birds, including the puffin (Fratercula arctica) and the Annex I, Birds Directive-listed species common tern (Sterna hirundo) and kittiwake (Rissa tridactyla); it may facilitate also the recolonisation of the islands by roseate tern (Sterna dougallii), a priority for conservation species. In addition, it is expected to have a positive impact on: waders such as the oystercatcher (Haematopus ostralegus) and ringed plover (Charadrius hiaticula); land birds such as the song thrush (Turdus philomelos) and house sparrow (Passer domesticus); the lesser white-toothed shrew (Crocidura suaveolens), for which Scilly is the only UK site; a range of invertebrates; and plants such as heather (Calluna vulgaris) that are adversely affected by rats. Expected results: The main immediate result of the project will be eradication of the brown rat population on St Agnes and Gugh. As a result, the 41.3 ha of habitat on these islands that is suitable for breeding storm petrels will be become accessible to this species, together with the 3 610 m of stone walls in which it could also nest. In addition, rat removal will render 43.7 ha of suitable habitat available to Manx shearwaters, which currently occupy less than 0.1 ha of this habitat. Over time, this should lead to significant increases in the populations of both species on these two islands (currently 17 pairs of Manx shearwater and zero pairs of storm petrel.