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Danish Common Eider Sex-Ratio Survey Recorded 63.3% Males, Down From 69.3% in 2024

Male and female common eiders
Conservation · Population & status

A nationwide Danish survey of common eiders (Somateria mollissima) found 63.3% males and 36.7% females among 22,090 birds analysed in March 2026. The result describes birds counted at selected coastal sites; it is not an estimate that exactly 63.3% of Denmark’s entire eider population is male.

Forty-one volunteer hunters submitted counts from 68 coastal locations. Ten locations with fewer than 20 eiders were excluded from the main analysis, leaving 58 locations across ten marine areas.

The male share fell from 69.3% in 2024 to 63.3% in 2026

Comparable Danish Hunters’ Association surveys recorded 63.6% males in 2011, 65.4% in 2021, 69.3% in 2024 and 63.3% in 2026. The change from 2024 to 2026 was statistically clear, while the 2026 ratio was not distinguishable from the 2011 result.

The 2026 result therefore represents a return towards the earlier survey level rather than a new historical low in male proportion.

Sex ratios varied strongly among marine areas

The 2026 female share ranged from 15.8% in the Wadden Sea to almost half in Smålandsfarvandet, where 49.3% of 2,171 birds were female. A 50% female share in the Baltic Sea was based on only 34 birds and is therefore much less informative.

Changes since 2024 also differed among regions: some marine areas shifted towards more females, others towards more males, and there was no single geographic pattern explaining the national change.

The survey samples mainly coastal resting birds

Sex was identified visually, and both resting and migrating birds could be included. In practice, however, the survey mainly covered coastal resting eiders, including sites close to breeding colonies. The report notes that this may overrepresent paired birds and produce a more even sex ratio than monitoring focused on migrating birds.

Spring migration counts at Hyllekrog, for example, have shown a lower female share. The two monitoring approaches sample different parts of the population, but both consistently show more males than females.

The female share matters for population monitoring

Female eiders are fully protected from hunting in Denmark, while males remain huntable. The report treats sex-ratio monitoring as one part of the evidence used to assess a declining population in which the number of females is especially important for reproductive output.

The 2026 survey confirms a persistent male-biased sex ratio but also shows why a single percentage should not be treated as a complete population census. Continued repeated monitoring is needed to distinguish long-term change from geographic and sampling variation.

Sources and image credit

  1. Sørensen, S. L., & Jacobsen, Z. (2026). Kønsfordeling blandt edderfugle i Danmark – Resultater fra Danmarks Jægerforbunds tælling af kønsfordelingen blandt edderfugle i Danmark marts 2026.Primary technical report. The analysed 2026 sample comprised 22,090 common eiders at 58 locations, with 63.3% males and 36.7% females; the report compares the result with 2011, 2021 and 2024 and discusses geographic and methodological variation.
  2. Danish Hunters Gather Key Data for Sustainable Eider HuntingSupporting announcement dated 30 June 2026 documenting publication of the March 2026 survey results and linking to the full Danish Hunters’ Association report.

Image: Martin Olsson — two male and two female common eiders at Hällsvik, near Gothenburg, Sweden, 8 April 2007; Wikimedia Commons; CC BY-SA 3.0. Representative mixed-sex image, not birds from the Danish survey. · CC BY-SA 3.0 · Source

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