Euphagus carolinus (Rusty Blackbird) from two different breeding populations in northeastern North America exhibit chain migration yet use the same region for stopover

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ABSTRACT Bird populations within the same species may follow different migratory strategies and phenology depending on their breeding location and latitude, and migratory strategies may be influenced by important stopover sites. Understanding these strategies and identifying important stopover sites is crucial for the conservation of species with regionally varying population trends. In this study, Euphagus carolinus (Rusty Blackbird) from 2 populations in eastern North America were affixed with NanoTag (Lotek) transmitters and tracked using the Motus Wildlife Tracking System to determine migratory routes and connectivity, stopover locations, and wintering areas. During fall migration, birds tagged at Observatoire d’oiseaux de Tadoussac, Québec and breeding sites in New England maintained separate migratory routes north of 43° latitude, as indicated by positive Mantel statistics of migratory connectivity, before converging on stopover areas in the Chesapeake and Delaware Bays region of the mid-Atlantic U.S. Migratory strategy differed between the 2 populations: birds from New England spent ~2 months longer at breeding latitudes than birds from Québec, and Québec birds spent more time at fall stopover sites and wintering latitudes. Birds from both populations made >1-week stopovers during spring and fall migrations and made long-distance (up to 645 km) nocturnal flights. The few winter detections suggested that E. carolinus from New England wintered at more southern latitudes than birds from Québec. Land cover data around stopover sites indicated that E. carolinus were positively associated with percent cover of wooded wetlands, croplands, and hay/pasture. Results from this study could help identify and protect regionally important stopover and wintering areas for E. carolinus, a species that has experienced dramatic long-term population declines linked to habitat loss in the nonbreeding range.