Quantifying the global threat to native birds from predation by non‐native birds on small islands

Although invasive non‐native species can adversely affect biodiversity in many ways, predation of native species by non‐native species on islands can be severely damaging. Results of numerous studies document non‐native birds preying on birds on islands, but our understanding of the number and type of species affected has been limited by the lack of a global review of these impacts. I identified the non‐native bird species that have been recorded preying on birds, the locations where this predation occurred, and the bird species affected. Because the impacts of non‐native birds can be particularly severe on small islands, I then identified the islands <500 km 2 around the world that are occupied by predatory non‐native birds. By taking into account their life‐history traits and predation history, I also identified the near‐threatened and threatened bird species on these islands that they may prey on. The results indicated that predation by non‐native birds was primarily a concern for threatened bird conservation on small islands; almost all predation impacts (91%) on near‐threatened and threatened birds were recorded on islands, and median island size was 106 km 2 . I also found non‐native bird predation was a poorly known and widespread potential threat to avian biodiversity; worldwide, 194 islands of <500 km 2 were occupied by predatory non‐native birds, but information on their impacts was unavailable for most of these islands. On them, where the impacts of non‐native species can be severe, non‐native birds may be preying on approximately 6% of the world's near‐threatened and threatened bird species. Four non‐native bird species I identified have been successfully eradicated from islands. If they were eradicated from the small islands they occupy, 70% of the near‐threatened and threatened bird species I identified would no longer be affected by nest predation by non‐native birds on small islands.