Annual‐Cycle Movements and Phenology of Black Scoters in Eastern North America

Abstract

Sea ducks exhibit complex movement patterns throughout their annual cycle; most species use distinct molting and staging sites during migration and disjunct breeding and wintering sites. Although research on black scoters (Melanitta americana) has investigated movements and habitat selection during winter, little is known about their annual‐cycle movements. We used satellite telemetry to identify individual variation in migratory routes and breeding areas for black scoters wintering along the Atlantic Coast, to assess migratory connectivity among wintering, staging, breeding, and molt sites, and to examine effects of breeding site attendance on movement patterns and phenology. Black scoters occupied wintering areas from Canadian Maritime provinces to the southeastern United States. Males used an average of 2.5 distinct winter areas compared to 1.1 areas for females, and within‐winter movements averaged 1,256 km/individual. Individuals used an average of 2.1 staging sites during the 45‐day pre‐breeding migration period, and almost all were detected in the Gulf of St. Lawrence. Males spent less time at breeding sites and departed them earlier than females. During post‐breeding migration, females took approximately 25 fewer days than males to migrate from breeding sites to molt and staging sites, and then wintering areas. Most individuals used molt sites in James and Hudson bays before migrating directly to coastal wintering sites, which took approximately 11 days and covered 1,524 km. Males tended to arrive at wintering areas 10 days earlier than females. Individuals wintering near one another did not breed closer together than expected by chance, suggesting weak spatial structuring of the Atlantic population. Females exhibited greater fidelity (4.5 km) to previously used breeding sites compared to males (60 km). A substantial number of birds bred west of Hudson Bay in the Barrenlands, suggesting this area is used more widely than believed previously. Hudson and James bays provided key habitat for black scoters that winter along the Atlantic Coast, with most individuals residing for >30% of their annual cycle in these bays. Relative to other species of sea duck along the Atlantic Coast, the Atlantic population of black scoter is more dispersed and mobile during winter but is more concentrated during migration. These results could have implications for future survey efforts designed to assess population trends of black scoters. © 2021 The Wildlife Society.

Evaluation of breeding distribution and chronology of North American scoters

“…Dissimilar migratory patterns among scoter species have been reported previously. Atlantic‐wintering black scoters (Lamb et al 2021) and Pacific‐wintering surf scoters (De La Cruz et al 2009, Takekawa et al 2011) are dispersed in winter and more concentrated during migration and breeding, whereas Atlantic‐wintering white‐winged scoters are more concentrated during winter and dispersed during migration (Meattey et al 2018, Lepage et al 2020). Identifying differences in migration and breeding timing is important for increasing our understanding of the comparative ecology of North American scoters.…”

“…Indeed, arrival and departure to breeding locations by Atlantic black scoters varies by longitude, where individuals breeding farther west (i.e. individuals with greater migration distances) arrive later, stay longer, and depart later than individuals breeding farther east (Lamb et al 2021). However, surf scoters wintering along the Pacific Coast show highly synchronous breeding regardless of wintering origin or differences in spring migration distance (De La Cruz et al 2009, Takekawa et al 2011), and previous tracking of white‐winged scoters tagged along the Atlantic Coast found no relationship between migration duration and total migration distance (Meattey et al 2018).…”

“…Savard et al (2007) suggested that surf scoter subadults likely remain in marine habitats throughout the summer; however, terrestrial isotopic signatures in immature male surf scoters suggest that subadult males may spend time in inland waters prior to molt (Budge and Gilliland 2007). Studies in surf, black, and white‐winged scoters demonstrate that males, subadults, and non‐breeding females typically leave breeding areas and begin post‐breeding remigial molt before breeding females (Savard et al 2007, Meattey et al 2018, Lepage et al 2020, Gilliland and Savard 2021, Lamb et al 2021). There is also evidence of differing habitat use among sexes, age groups, and between successful and unsuccessful breeders (Iverson et al 2004, Meattey et al 2018, Lepage et al 2020, Lamb et al 2021).…”

“…We evaluated whether variation in arrival and departure dates differed by species, wintering origin (Atlantic or Pacific), an interaction between species and wintering origin, age class (one‐year‐old subadult, two‐year‐old subadult, or adult), and/or snow‐free date using linear mixed effects models (LMMs). Lamb et al (2021) found sex‐related differences in migration timing in Atlantic black scoters. We thus included sex as a covariate in our analysis of arrival date to further account for this factor.…”

“…See Table 2 1987, Smith 1995. It is also important from a conservation perspective, as different segments of scoter populations could be exposed to dissimilar environmental and ecological pressures (Iverson et al 2004, Lamb et al 2021), and better understanding these pressures and their impacts on scoter populations can inform decisions to help mitigate risks.…”