Adams Island (9,693 ha) is the second-largest island in the Auckland Islands group, and the largest island in New Zealand on which introduced mammals have never become established. Adams Island is forested on the northern sheltered parts of its coastline, and has shrubland, grassland, and fellfield at higher altitudes, and herb-field in fertile open sites. Sheer cliffs dominate the exposed, southern side of the island, and above them, narrow shelves support lush herb-fields. This diversity of habitat in close proximity supports unique communities of birds, with most species in remarkable abundance due to the absence of introduced predators. With the notable exception of the Auckland Island merganser (Mergus australis
), the island’s birdlife is close to what it would have been in pre-human times, and includes high densities of species that are now rare or missing on nearby Auckland Island. This paper describes the island, the history of ornithological exploration, and the past and current state of the avifauna. The 48 extant bird species recorded from the island comprise 22 land birds and 26 seabirds, of which 34 species (16 land birds and 18 seabirds) have been recorded breeding or are likely to be breeding there. Eight species introduced to New Zealand have also made their way to Adams Island, and six probably breed there.