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Angerm√ľnde, Germany

Bellebaum J.,Wiesenstrasse 9 | Madlow W.,In der Feldmark 7
Ardea | Year: 2015

Adult sex ratio in ducks is male-biased, probably due to higher mortality of incubating females. In an introduced population of Mandarin Ducks Aix galericulata in Berlin and Potsdam, adult sex ratio (proportion of males) was 0.65 (95% confidence interval 0.64-0.67). Annual apparent survival of 163 colour-ringed birds during 2003-2012 was 0.65 (0.55-0.76) for first year and 0.66 (0.60-0.72) for adult males, and 0.47 (0.25-0.69) for first year and 0.57 (0.48-0.66) for adult females. Female mortality but not male mortality peaked during the breeding season. A Leslie matrix model based on productivity and survival rates in the study population estimated an adult sex ratio of 0.64, or 0.67 when first-year birds were excluded. The similarity between observed adult sex ratio and model estimates based on survival suggests that the male-bias might be fully explained by sex differences in survival. Source

Bellebaum J.,Wiesenstrasse 9 | Kube J.,Dorfstr. 20 | Schulz A.,Institute fur Angewandte Okosystemforschung GmbH | Skov H.,DHI | Wendeln H.,IBL Umweltplanung GmbH
Ornis Fennica | Year: 2014

Abundance of Long-tailed Ducks Clangula hyemalis wintering in the Pomeranian Bay wasmonitored between 1988 and 2014, using both ship-based and aerial surveys and correcting for distance dependent detection. Aerial surveys were conducted using an improved transect division and a double observer design to estimate detection probability near the transect line. As the latter probability was considerably below 1, we applied an additional correction factor for observer efficiency. After correcting for observer efficiency in aerial surveys, the two methodological approaches yielded similar densities, though an apparent underestimation in aerial surveys warrants further cross-validation. Density estimates from both platforms were merged for further analysis. After reaching peak levels in 1992 and 1993, Long-tailed Duck winter densities in the Pomeranian Bay declined by 82% until 2010. This decline was part of an overall decline in numbers throughout the Baltic Sea. An apparent increase since 2010, whichwas likely due to local ice-induced movements, indicates that habitats in the study area may still support high densities today. Source

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