Understanding how bird populations are spatially structured throughout their annual cycles is critical to identifying when and where these populations are most limited. Canadian breeding populations of Horned Grebe (Podiceps auritus cornutus; hereafter grebe) appear to have substantially declined since 1970, and uncertainty in annual movements of this species limits our understanding of factors affecting their population dynamics. To address this knowledge gap and identify grebes’ migration routes and non-breeding areas, we fit light-level geolocators and sampled feathers for stable isotopes (carbon δ13C, nitrogen δ15N, hydrogen δ2H) in Prairie and Boreal portions of the grebe breeding range between 2020 and 2023. Geolocator data (n = 18 birds) indicated that grebes undertook southeastern fall migratory movements and occupied marine and freshwater non-breeding locations across a large geographic area including southeastern Canada, the Midwest and southern United States, the Atlantic Coast, and the Gulf of Mexico. Geolocator and feather stable isotope data confirmed weak migratory connectivity and separated birds into four distinct non-breeding ground clusters. Our results suggest threats that grebes experience on non-breeding areas may have diffuse effects on breeding populations and further provide novel information on the migration ecology and spatial linkages of two breeding populations of grebes in North America. Taken together, these findings will help to inform development and implementation of management strategies for this species of conservation concern.