Conservation implications of reproductive success of American Oystercatchers in an urbanized barrier island complex

Urbanization on the barrier islands along the Atlantic coast of North America has severely altered the traditional breeding habitat for many ground-nesting waterbirds in this region, including the American Oystercatcher Haematopus palliatus. We used an information-theoretic approach to analyze various humaninduced effects on oystercatcher daily nest survival rates and overall reproductive performance in an urbanized coastal ecosystem. We used explanatory variables including habitat type, level of human disturbance, presence of mammalian predators, proximity to gull colonies and nest height above sea level as nest-specific covariates in our models to explore their effects on the daily survival rates of clutches and broods separately. We found an overall reproductive success rate of 7%, which is far below the level necessary to sustain the population. The principal factor negatively influencing daily survival rates of clutches and broods was the presence of predators, with mammalian predators affecting clutches and gulls affecting broods. The reproductive success rate on predator-free inlet and back-bay islands (25%) was an order of magnitude greater than the rate reported on barrier islands (2%), which have relatively high densities of predatory mammals. Ours is one of the few studies to comprehensively evaluate the breeding success of American Oystercatchers within alternative breeding habitats such as inlet and back-bay islands. Our results confirm the management conclusions of others that the best way to ensure the long-term population viability of American Oystercatchers is to concentrate management on these alternative habitats. This protection strategy likely also has benefits for other ground-nesting waterbirds.