Late-Holocene seabird palaeodietary record from Ganquan Island, South China Sea

Seabirds migrate between marine and island ecosystems, and their subfossil remains have been widely used in palaeoecological studies. Bone subfossils of seabirds were collected from Ganquan Island of the Xisha archipelago, South China Sea. Stable isotopes (δ15N and δ13C) in well-preserved ancient collagen samples were analyzed to investigate seabird palaeodiets over the past 2200 years. Stable isotope-based palaeodietary analysis indicates a significant change in seabirds' foraging behavior at 1200 BP. A long-term connection between seabird population and their trophic levels has been identified. High-trophic prey contributed more to the diet of birds during the period of relatively high seabird abundance at 1200–200 BP. Both collagen δ15N and δ13C suggest that intra/inter-specific competitions may force seabirds to dive deeper or travel further to catch prey.