Predation and food–weather interactions drive colony collapse in a managed metapopulation of Arctic Terns (Sterna paradisaea)

Seabirds are considered bioindicators of bottom-up ecosystem processes, owing to seabirds’ dependence on marine prey. However, ground-nesting seabirds are susceptible to predation, which can limit their use as bioindicators. Machias Seal Island (MSI) supported the largest colony of Arctic Terns (Sterna paradisaea Pontoppidan, 1763) in the Gulf of Maine metapopulation, but prolonged breeding failure led ~90% of terns to abandon the colony in 2006. We analyzed twelve years of food, weather and predation data using logistic regression models to determine which had the strongest influence on breeding success. Food-weather interactions were important; under low rainfall, more euphausiids (Meganyctiphanes norvegica Sars, 1857) in the diet increased breeding success, but euphausiids had a negative effect as rainfall became moderate or high. Predation by Herring Gulls (Larus argentatus Pontoppidan, 1763) increased following the cessation of lethal predator control; we identified a predation threshold of 25%, beyo...