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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