Interactions between invasive mammals and their effects on Red-billed Tropicbird (Phaethon aethereus) nesting productivity



Red-billed Tropicbirds (Phaethon aethereus) are cavity-nesting seabirds with important nesting colonies on Saba and Sint Eustatius in the Dutch Caribbean. Breeding productivity has been steadily declining and nest failure is primarily attributed to the presence of invasive mammalian predators. Camera traps were deployed to determine the extent of invasive species presence and impact. Cats, rats, and goats as well as native land crabs and lizards were present on both islands and actively visiting nest sites. The positive relationship between goat visitation and cat visitation suggests that goats may be facilitating cat predation by increasing visibility and accessibility to nests. Disturbance from goats may be causing nest abandonment by breeding adults, which warrants further study. A significant proportion of nests surveyed (n=106) were failures (n=71). It can be inferred that invasive mammalian presence at those sites is contributing to nest failure. There is not enough evidence to draw any conclusions on the possible impact of native predators. Further and more extensive monitoring is recommended to better quantify impacts and invasive species behaviour for eradication programme design.