Analysis of 50 years (1974/75–2023/24) of 123 Christmas Bird Counts along the east and west coasts of North America and in the Great Lakes region reveals a substantial decline of the White-winged Scoter (Melanitta deglandi) along the more southern segments of its winter range. All 16 of the California count circles examined showed a decline, which from Sonoma County south averaged 8.5% per year over the 50 years. The segment from Washington to northwestern California saw a smaller but still significant decline of 2.2% per year, while on counts in British Columbia and Alaska White-winged Scoter numbers increased slightly, at rate of 1.4% per year. On the east coast, from New Jersey south to Florida, White-winged Scoter numbers declined 5.8% per year, as well as in 18 of the 22 count circles in that segment. The northern and central segments of the east coast showed smaller but significant declines of 1.4 and 0.6% per year, respectively. The Great Lakes host fewer wintering White-winged Scoters than does either coast; Christmas Bird Count data from that region showed no clear trend. It is unclear whether our findings reflect a decline in the White-winged Scoter’s population rangewide, a northward shift in the coastal nonbreeding range into areas not well surveyed by Christmas Bird Counts, or combination of the two. The increase in sea-surface temperatures on both coasts of approximately 1o C since the 1970s may be a factor.