Dietary ecology of the Glaucous-winged Gull (Larus glaucescens) in the Pacific North-West: conventional and stable isotope techniques and implications for eco-toxicology monitoring

Effective use of seabirds in ecotoxicology monitoring programs (e.g. Canada’s Chemical Management Plan) requires detailed knowledge of their ecology. I examined the dietary ecology of Glaucous-winged Gulls (Larus glaucescens) in British Columbia, using conventional diet analysis and stable isotope analysis. Conventional analysis suggests that gulls forage in an opportunistic manner, with a variety of prey types consumed at a colony closest to urban development, but that marine sources (fish, invertebrates) were the predominant dietary component at all colonies. However, variation in chick diet between 2009 and 2010 indicates that diet can vary considerably on a short time scale. Compared with historical records, gulls currently consume less food from anthropogenic sources and more fish in the Salish Sea, whereas at Cleland Island diet has remained marine-based over time. Stable isotope analysis confirmed that gulls at all three monitored colonies fed primarily on near-shore marine prey at a high trophic level.