Characterization of the migratory distribution, connectivity, philopatry and timing of the western North American Harlequin Duck (Histrionicus histrionicus) population

Anthropogenic impacts such as habitat loss and degradation, disrupted food sources, and altered climactic processes pose diverse challenges to wildlife population viability. Migratory wildlife are vulnerable to such impacts across multiple geographically disparate habitats upon which they rely as an ecologically connected network. Sea ducks are especially susceptible as they rely on terrestrial and marine habitats throughout their annual migratory cycles. Among sea ducks, the Harlequin duck is exceptional for its migration between freshwater montane streams and coastal marine habitats, status as a species of concern among much of its range, and dearth of population information. Simultaneously, its unique life history characteristics renders it a valuable indicator species. I sought to address a priority science need concerning Harlequin Duck movement ecology by analyzing its temporal and spatial migratory structure across six broad regions in northwestern North America using a collection of satellite telemetry datasets. Together, these datasets comprised 136 individuals captured across four U.S. states and two Canadian provinces. Migratory location and timing data were analyzed to determine spatial distribution, migration chronology, philopatry, migratory connectivity, and the relative importance of geographic and climatic drivers on migration timing. My analysis demonstrated strong philopatry to breeding, moulting, and wintering sites and moderate philopatry to stopover sites. Migratory connectivity between breeding, moulting, and wintering stages was low, suggesting a mixing of individuals from different geographic regions. Significant distinctions in migration timing were detected between sex, breeding/capture regions, and years. Latitude, longitude, breeding elevation, distance traveled, and cumulative thaw degree days were found to be important predictors of migration timing. These results revealed spatio-temporal structure in Harlequin Duck migration, with timing of annual migratory events being influenced heavily by location-specific conditions in breeding regions. Identification of shared core use areas among multiple population segments can be used to guide habitat conservation efforts. Additionally, geographic distinctions in migration timing can be used to inform individual state and provincial species management and recovery plans.

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