Biometrics of the mute swan Cygnus olor based on a sample of 45 individuals

In the winter of 1987, 45 mute swans were found dead on the banks of the Grevelingenmeer (Lake Grevelingen) in The Netherlands. A total of 12 measurements on the specimens ‘in the flesh’ were taken in the field and later, after maceration, another eight measurements on the cleaned skulls were taken. The sex of all specimens was established anatomically. This article presents the results of the biometrical analysis of these measurements. The best method for establishing the sex of mute swans based on external measurements appeared to be the length of the middle toe. Several other measurements were examined and their usefulness for sexing is discussed. Mute swan specimens from the collection of the Natural History Museum Rotterdam were used to test the significance of the findings.