| Summary: | 1. Rats have reached about 80 % of the world’s islands and are among the most successful invasive mammals. Rats are opportunistic predators that are notorious for their impact on a variety of animal and plant species. However, little documented evidence on the complexities of these interactions is available. 2. In our study, we assessed the impact of black rats Rattus rattus introduced on a small uninhabited island with a relatively simple ecosystem, Surprise Island, New Caledonia. We also compared the diet of R. rattus in the presence and absence of breeding seabirds, assessing the dietary compensation for this potentially important food source. From 2002 to 2005, we used live trapping studies combined with stable isotope analysis and conventional diet analyses (direct observations, gut and faecal contents) to characterize the diet of rats. 3. Our results suggest a heavy predatory impact on seabirds, which could constitute as much as 24 % of the rat diet. Moreover, in the absence of birds, rats compensated marginally by preying more heavily on other components of their diet but mostly acquired a new resource. They shifted their diet by preying heavily upon another endangered species, the hatchlings of sea turtles Chelonia mydas, which could constitute the main resource in the diet of R. rattus in those periods. Abundance, body condition
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