Plastic exposure in relation to breeding stage and diet in an urbanized gull species

Anthropogenic debris, particularly plastic, is ubiquitous and increasing in the environment. The St. Lawrence is a biodiverse ecosystem facing cumulative stressors, yet wildlife exposure to anthropogenic debris remains poorly understood. As opportunistic feeders, gulls present a unique opportunity for monitoring plastic pollution. Their foraging habits can shift when chicks hatch, potentially influencing debris exposure. We assessed debris ingestion and diet in adult American herring gulls (Larus smithsonianus) throughout the breeding season using pellets from Île de Bellechasse, Québec. Approximately 50 % of pellets contained debris, of which 80 % contained plastic. The occurrence, count and mass of debris items in pellets decreased significantly from incubation to early chick-rearing. Their mainly terrestrial diet was least diverse during early chick-rearing. Our findings suggest that urbanized breeding herring gulls rely heavily on anthropogenic resources, increasing debris exposure for adults and chicks and indicating the need for improved waste-management practices to protect wildlife.