Abstract

Twenty-nine species of helminths were found in 145 ring billed gulls collected in southern Quebec. No significant differences were observed in the helminth communities of gulls collected in May from four nesting sites (Montreal, Sorel, Quebec City, Les Pilliers), suggesting that infective pools are widespread along the St. Lawrence. Adults arriving in April had light infections. Infection levels and diversity increased during the nesting season, and over the course of the summer, due mainly to recruitment of helminths transmitted by fish. Communities in young gulls collected on the nesting island at Montreal displayed little diversity, and were dominated by Plagiorchis multiglandularis. Following dispersal from the colony, helminth diversity increased rapidly in young gulls. The communities in adults and juveniles were most diverse in August, at which time they were comparable. Based on the August collections, there seems to be little yearly variation in the helminth communities of adult and juvenile gulls, which tended to be more similar at the same time each year than they are at different times within a year. Infection levels and community diversity declined drastically in young gulls by November, apparently due to natural attrition of existing infections and the lack of recruitment of new ones. Ring billed gulls appear to sustain low levels of infections over winter, as suggested by the light infections seen on arrival. They quickly acquire a characteristic suite of helminth species that appears to occur commonly in gulls along the St. Lawrence.