Red Knots (Calidris canutus) that spend winter in the southeastern United States are known to have been genetically separated from their congeners that migrate to Patagonian wintering grounds for about 12,000 years. We examined and documented differences between the two groups in their use of southward migration stopover locations, flight feather molt, fidelity to wintering zones, and differences in mass at southward migration stopover locations. Red Knots wintering in the southeastern United States do so consistently, and knots wintering in Patagonia have not changed to wintering in the southeastern United States. The two wintering groups have distinct differences in their nonbreeding season biology (e.g., migration strategies, chronology of pre-basic molt), and these differences have been maintained for decades if not millennia.