Physiological health of wintering glaucous-winged gulls in coastal British Columbia

Gulls (Laridae) use natural and urban environments and are useful 'biomonitors' of coastal ecosystem health. Here, we assessed physiological health of glaucous-winged gulls (Larus glaucescens, GWGU) wintering in the Salish Sea, British Columbia, Canada, a biodiverse region undergoing rapid anthropogenic change. We measured six physiological health biomarkers (blood glucose, triglycerides, haemoglobin, haematocrit, reactive oxygen metabolites and total antioxidants). Gulls sampled on the west coast of Vancouver Island had higher blood δ ¹³C and δ ¹⁵N values likely reflecting more marine diets compared with birds sampled in the Lower Mainland of Vancouver and in associated urban habitats such as landfills but terrestrial isotopic inputs are confounding. We found few differences in any of the six physiological markers in relation to region and habitat, or in overall indices of 'health' and 'nutritional state' using principal components analysis, even though these were characterized by varying levels of urban development and anthropogenic activity. Furthermore, individual variation in physiological traits was independent of individual variation in blood δ ¹³C and δ ¹⁵N values. This likely reflects the fact that we sampled 'physiologically homeostatic' individuals at all locations and habitats. Our study establishes reference values for six putative 'health' biomarkers, highlighting important covariates that need to be considered (e.g. sex, location) and provides a foundation for long-term physiological monitoring in relation to future anthropogenic impacts in this region.