VERKADE H (2022) Sex ratio in Pochard Aythya ferina and Tufted Duck A. fuligula on an estate in the west of the Netherlands. LIMOSA 95 (3): 127-133.

During 19 winters (2001-20) the sexratio of Pochard and Tufted Duck was noted during weekly counts of waterbirds on a small pond at the Nieuw-Leeuwenhorst estate, near Noordwijkerhout. From being a stable population, the number of Pochards declined and disappeared almost completely in 2015 (Fig. 1). During that period Pochards arrived later at the study site each year and left earlier (Fig. 2). Tufted Duck is present year-round and strongly increased during the study period.
During 2001-05 the proportion of male Pochards was 37%, in the next five years the population decreased, with the proportion of males growing to 47%. In 2011-15 only a small number of Pochards wintered on the pond, with a sex ratio of 70% males (Fig. 3). The number of males in the Tufted Duck population was stable (around 56%) during the whole study period. This is in line with observations in the Netherlands and elsewhere in Europe. The sex ratio varied throughout the season, with the highest percentage of males in spring, when the number of Tufted Ducks peaked (Fig. 4).
The number of female Pochards declined especially in the main breeding areas in Eastern Europe. Large numbers winter in Western Europe. Males are dominant to females, and occupy the best winter spots, such as large open shallow waters, whereas females rely on smaller water bodies. Probably the pond at the Nieuw-Leeuwenhorst estate was a suboptimal wintering area with initially a majority of female birds. With the steeper decline of females, the sex ratio changed in favor of males during the study period.

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