Using Movement Data from Satellite Telemetry to Infer Nesting Status and Breeding Propensity of a Colonial Breeder, the American Common Eider (somateria Mollissima Dresseri)

American common eiders (Somateria mollissima dresseri) are ecologically and culturally important sea ducks in northeastern North America. Female eiders may not breed every year, making breeding propensity (the proportion of sexually mature females breeding in a given year) a key demographic parameter. We investigated regional variation in breeding propensity across the subspecies’ range using fine-scale movement data collected by satellite telemetry. Females were captured across six regions (Maine, New Brunswick, Nova Scotia, Québec, Newfoundland, Labrador) and fitted with platform terminal transmitters (PTT). After filtering, movement data from 123 individuals over three years (2022–2024), resulting in 197 unique bird-breeding seasons, were analyzed using a three-state hidden Markov model. Three behavioral movement states—limited, localized, and mobile —served as proxies for nesting, foraging/loafing, and transit, respectively. A decision tree classified breeding status into successful nesting, failed nesting, prospecting, or skipped breeding. Overall breeding propensity was only 53