Latitudinal and seasonal variation in non-breeding survival of Surf and White-winged Scoters

To understand wildlife population dynamics and identify when and where demographic or distributional constraints may exist within the annual cycle, it is important to quantify timing and sources of variation in demographic attributes. I documented survival of surf and white-winged scoters during remigial molt, and surf scoter survival during winter, at multiple sites along the Pacific coast of North America. I detected no mortalities during remigial molt, indicating high survival within this annual cycle stage, irrespective of latitude, species, or age and sex cohort. Winter survival was related to location, period of winter, cohort, and mass. These results highlighted times (mid-winter) and locations (range peripheries) in which mortality was elevated for some cohorts, and that attributes of individuals, specifically mass, was positively related to survival. My findings indicate mechanisms leading to observed population dynamics and distributions, as well as times and places in which conservation action would be most productive.