Diet specialization in American Oystercatchers (Haematopus palliatus) breeding in Virginia, U.S.A.

R scripts, data, and GPS track animations accompanying the manuscript “Diet specialization in American Oystercatchers (Haematopus palliatus) breeding in Virginia, U.S.A.” Abstract.— Diet specialization in breeding American Oystercatchers (Haematopus palliatus) was documented on a barrier island in Virginia, U.S.A. in 2022 and 2023. Behavioral observations (n = 816 observations) of adults foraging for themselves and their chicks, and GPS tracking (n = 20,202 GPS fixes) identified 12 individuals that specialized feeding almost exclusively at oceanside shorelines on mole crabs (Emerita talpoida) (>90% of their diet). Ten generalists fed at shorelines plus bayside mudflats, eating six species of bivalves and mole crabs. Diet specialization was best explained by distance from mussels (Modiolus demissus), the most profitable prey species, and the energy costs of traveling to mussels. Individuals that had to travel >280 m to reach mussels specialized instead on nearby mole crabs, the second most profitable prey. Traveling to mussels would cost specialists 42% more energy than traveling to forage on mole crabs. There were no significant differences based on diet for maximum foraging distance, food profitability, adult body condition, handling time of mole crabs, chick provisioning rates or chick energy intake rates. Adults might specialize on mole crabs to conserve energy for future breeding seasons. Given this diet specialization, American Oystercatcher conservation efforts might include managing beaches for healthy mole crab populations. Note. Wader Quest also funded this research.