The movement ecology and physiological health of glaucous-winged gulls wintering in the Salish Sea

Gulls (Laridae) use natural and urban environments and are useful 'biomonitors' of coastal ecosystem health. I studied movement ecology (using GPS tags) and physiological health (from blood samples) in glaucous-winged gulls (Larus glaucescens; GWGU) during winter in the Salish Sea, a region undergoing rapid anthropogenic change. GWGUs exhibited high wintering region fidelity within the Salish Sea and exploited landfills and Pacific herring spawn activity. These resources were especially important for migrant GWGUs (22% of the population). Daytime habitat use varied among individuals, but all GWGUs roosted on water at night. There was marked individual variation in, and covariation among, physiological traits (glucose, triglycerides, hemoglobin, hematocrit, and oxidative state). However, region and habitat type where birds were captured did not predict variation in health biomarkers, even though these included varying levels of urban development and anthropogenic activity. This study establishes reference values for health biomarkers for long-term monitoring of future anthropogenic impacts in this region.