Spring migration patterns of red knots in the Southeast United States disentangled using automated telemetry

Abstract Background and Methods Shorebirds evolved flexibility in their migration strategies, with demonstrated variation even within the same population. Research in the last decade revealed diverse migration routes for red knots using the Western Atlantic flyway. Red Knots use the Southeast United States (North and South Carolina, Georgia, and Florida) as a stopover during north and southbound migration and during the winter. We examined northbound red knot migration routes and timing from the Southeast United States using an automated telemetry network. Our primary goal was to evaluate the relative use of an Atlantic migratory route through Delaware Bayversus an inland route through the Great Lakes en route to Arctic breeding grounds and to identify areas of apparent stopovers. Secondarily, we explored the association of red knot routes and ground speeds with prevailing atmospheric conditions. Results Most Red Knots migrating north from the Southeast United States skipped or likely skipped Delaware Bay (73%) while 27% of the knots stopped in Delaware Bay for at least 1 day. Most birds that skipped Delaware Bay traveled north, through the eastern Great Lake Basin. A few knots used an Atlantic Coast strategy that did not include Delaware Bay, relying instead on the areas around Chesapeake Bay or New York Bay for stopovers. We did not detect stopovers in the Great Lakes Basin suggesting that knots move quickly through this region. Nearly half of the red knots were detected in either James Bay or Hudson Bay with the first day of detection ranging from 19 May to 7 June. Nearly 80% of migratory trajectories were associated with tailwinds at departure. Conclusions Most knots tracked in our study did not stop in the Great Lakes, thus making the Southeast United States the last terminal stopover for some knots before reaching Arctic habitats. This study demonstrates the diversity of red knot spring migration routes and underscores how critically important the Southeast United States is as a spring stopover site for red knots. Future conservation planning must include the full network of sites that support the varied migratory routes and strategies used by this declining shorebird species.