Cumulative impact of rats and coypu on nesting waterbirds: first evidences from a smal Mediteranean wetland (Central Italy)

In this short report, we provide evidences of a cumulative impact of two introduced and invasive rodent species, the brown rat (Rattus norvegicus) and the coypu (Myocastor coypu), on three common waterbird in a Mediterranean remnant wetland. We used digital photocameras to evaluate the damage and predation rate on both natural and dummy nests. In spring 2011, six out of eight natural nests were preyed or destroyed by three species: marsh harrier (Circus aeruginosus; egg predation), brown rat and coypu. In three cases, we obtained evidences of a multiple impact by two species (coypu and either marsh harrier or brown rat) on the same nest. Five out of eight dummy nests showed both egg predation by brown rat and damage by coypu. These three species preyed on and/or destroyed 80.6% of 31 natural eggs and 62.5% of 16 dummy eggs. Although based on relatively few observations, we provide the first direct evidence of a cumulative impact of brown rat and coypu on waterbird nests in a Mediterranean wetland and corroborate the hypothesis that these remnant wetlands may be considered sink habitats for many indigenous waterbirds.