Presented by Christian Roy - Email: email@example.comConcern over population status and the adequacy of operational breeding waterfowl surveys for sea duck and scaup populations persists. Large areas of the Boreal-Arctic transition zone of Canada (Taiga Plains and Shield ecoregions) are excluded from operational breeding waterfowl surveys. Recent experimental surveys and satellite telemetry have suggested its importance to breeding populations of these species but there remains uncertainty about the area’s importance to continental waterfowl populations. We conducted experimental helicopter-based breeding waterfowl surveys at 6 sites (20,000km2 each) located from Northern Quebec to the Northwest Territories, between 2017 and 2019. A total of 20-26 plots (25 km2) were surveyed at each site. The surveys were timed to coincide with the pre-laying and early-laying period for scoters. A double-dependent observer approach was used, allowing observed densities to be corrected for detection. Densities of sea ducks and scaup in aggregate were high at all sites, ranging from 3.6/km2 to 5.6/km2, exceeding 10/km2 on some plots. The most abundant species were scoters and scaup: tundra-dominated sites had higher densities of Black scoters and Greater scaup, White-winged scoters and Lesser scaup were at higher densities at more forested sites, and Surf scoters were more evenly distributed across sites. Maximum densities for Black scoters were 1.35/km2 [95%CI: 1.33 - 1.38]; Surf scoter 0.89/km2 [0.89 – 0.90]; White-winged scoter 0.57/km2 [0.57 – 0.59]; Greater scaup 0.39/km2 [0.38 - 0.39]; Lesser scaup 1.29/km2 [1.29 – 1.29]; as well as pooled scoters 2.34/km2 [2.32 – 2.37] and scaup 3.40/km2 [3.40 – 3.41]. More than 90% of all observations were of indicated pairs showing that these sites were terminal breeding areas for these five species. We will explore inter-annual variation in densities with 2019 survey data. Observed densities are high for diving ducks and sea ducks and clearly show the importance of the Boreal-Arctic transition zone for waterfowl production.