Comparing and contrasting migration patterns in Sanderlings and Red Knots: insights from the Motus Wildlife Tracking System

Limited data suggest that the North American Midcontinent Flyway may be an important migration route for long-distance migratory shorebirds, such as Sanderlings Calidris alba and Red Knots C. canutus, but information on migration paths, staging sites, and migration timing in the interior relative to coastal areas is largely unknown. Here, we explored migration patterns of tagged Sanderlings and Red Knots, to better understand use of the Midcontinent Flyway. Between 2015 and 2018, we radio-tagged 120 Sanderlings and 40 Red Knots in the Gulf of Mexico and 147 Sanderlings at Chaplin Lake, Saskatchewan, Canada, and tracked migration movements using the Motus Wildlife Tracking System. Motus-derived patterns were corroborated by eBird data. Most (81%) radio-tagged Sanderlings detected on both northward and southward migrations underwent an elliptical migration pattern, with more northbound migrants detected in the Midcontinent Flyway (95%) and more southbound migrants detected in the Atlantic Flyway (85%). In a comparison of all detected staging locations, staging duration for Sanderlings was similar on northward (2.2–19.7 d) and southward (2.4–23.7 d) migration, with individuals travelling northward at minimum speeds of 45–866 km/d and southward at 50–2,339 km/d. Similar to Sanderling, 89% of Gulf-tagged Red Knots migrated northward in the interior. Southward detections of Red Knots were restricted to Hudson and James Bays and the coast of Massachusetts, USA. For both species, staging areas were predominantly in Saskatchewan during northward migration and at Hudson Bay, James Bay, Delaware Bay, and the Great Lakes during southward migration. We conclude that the Midcontinent Flyway is an essential but understudied northbound migration route for both Sanderlings and Red Knots, which share common staging areas and similar migration schedules. Ongoing expansion of the Motus network will be important for increasing our understanding of shorebird migration and for prioritizing conservation efforts at key shorebird staging sites throughout the Midcontinent region.