Diet and ectoparasites of ring-billed gull chicks in a marine environment on Prince Edward Island

This thesis has two distinct foci. First, I investigated the diet of Ring-billed Gull chicks in a marine environment, on Prince Edward Island (PED), using soft regurgitant collection and stable isotope (δ¹³C and δ¹⁵N) analysis of both regurgitants and blood samples. I compared isotopic signatures of blood of Ring-billed Gull chicks to blood of chicks from sympatrically nesting Herring and Great Black-backed Gulls. Regurgitant data suggested insects, earthworms, and marine fish were the most common prey items of Ring-billed Gull chicks. Stable isotope analysis of blood suggested a more marine (enriched δ¹³C) and higher trophic level (enriched δ¹⁵N) diet of Great Black-backed Gull chicks compared to that of chicks of both Herring and Ring-billed Gulls. A two-source mixing model using stable isotope analysis of Ring-billed Gull chick regurgitants and blood estimated that 26 - 51% of Ring-billed Gull chick diet came from the marine environment, whereas estimates for Herring and Great Black-backed Gulls suggested 35 - 51%, and 73 - 77%, respectively. Thus, Ring-billed Gulls use marine food sources to feed their young when nesting in a marine environment. Furthermore, Great Black- backed Gulls feed their young more marine food than both Herring and Ring-billed Gulls. In the second part of this thesis, I investigated relationships among stress, immunocompetence, and ectoparasite loads of Ring-billed Gull chicks. Ring-billed Gull chicks from PEI host three species of lice: Quadraceps punctatus, Saemundsonnia lari, and Austromenopon transversum. Immunocompetence was assessed with a phytohaemagglutinin skin assay (PHA) and with differential leukocyte counts, while stress was assessed using the heterophil to lymphocyte ratio (H/L). Significant relationships were not observed among PHA, H/L, and louse loads. However, greater total louse loads and numbers of A. transversum were associated with higher proportions of leukocytes that were eosinophils. Eosinophils are involved with the innate immune response, the first line of defence against parasites. Furthermore, larger chicks had more lice. Overall, louse load was not linked with stress or PHA response but was associated with the innate immune system of Ring-billed Gull chicks, as measured by eosinophils.

Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.