LE3 .A278 2006

2006

Shutler, Dave
Wilson, Brian

Acadia University

Bachelor of Science

Honours

Biology

Biology

Differences in the size of cloacae can be used to sex some monomorphic seabirds. Reproductive females generally have larger and less elastic cloacae than males as a consequence of egg-laying. My first objective was to determine if cloacal measurements could be used to sex Leach’s storm-petrels. Cloacal measurements were taken from individuals of unknown and known laying dates, and sex was determined by molecular analysis of DNA isolated from feather and blood samples. Discriminant function analysis of cloacal measurements correctly sexed a maximum of 67% of petrels, suggesting cloacal measurements are not a reliable indicator of sex in this species. The release of hormones, such as corticosterone, often accelerates in response to immediate and chronic stimuli that present a threat to survival. Baseline plasma corticosterone concentrations (hereafter CORT) may be used as an indicator of chronic stress, which may be elevated during egg-laying, nestling provisioning, or when ectoparasite loads are high. My second objective was to assess the variation in CORT in Leach’s storm-petrels, a long-lived colonial seabird. I tested for a relationship between CORT and sex, reproductive stage, and ectoparasite load in petrels captured by spotlighting and grubbing on Bon Portage Island. The approximate reproductive stage of nesting petrels was determined by candling eggs. Ectoparasites were sampled by dustruffling. Corticosterone was assayed from plasma using an enzyme immunoassay. Females had significantly higher CORT than males, and seasonal variation in CORT was present, however, there was no relationship between CORT and ectoparasite load.

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