Effect of habitat use and diet on the gastrointestinal parasite community of an avian omnivore from an urbanized environment

With urbanization, anthropogenic foods have grown in importance for several species. A shift away from natural foods is likely to affect trophically transmitted parasites, although this has received limited attention in urban-adapted avian omnivores. We examined the effect of habitat use and diet on gastrointestinal parasite assemblages of Ring-billed Gulls (Larus delawarensis Ord, 1815) breeding in an urbanized region (Montréal, Quebec, Canada) using three approaches depicting different temporal scales. Birds were fitted with global positioning system data loggers to determine habitat-use patterns during a 2–3 day period. Stomach contents were examined, providing dietary information during the preceding hours. Liver carbon (δ 13 C) and nitrogen (δ 15 N) stable isotope signatures served as proxy of nutrient assimilation during the preceding 10 days. Endoparasite community variations were best explained by δ 13 C and δ 15 N ratios. Individuals with lower δ 15 N had lower parasite abundance, while δ 13 C was enriched in birds with less diverse parasites (fewer helminth genera). Tissue depletion in 15 N in Ring-billed Gulls from this colony has previously been associated with predominant consumption of human-related foods. The present study supports the hypothesis that Ring-billed Gulls exhibiting preference for anthropogenic food sources encounter fewer trophically transmitted parasites, which may have contributed, in part, to their population expansion during the last century.