Unequal Siblings
Three of four cygnets of the mute swan family in the Floridsdorfer Waserpark.
Two cygnets aren't grey, as is the norm, but white. They are so-called ‘Polish swans’. This is a colour morph that hatches from the egg with white plumage and is therefore also known as ‘immutabilis swan’, as the colour of the plumage does not change in the course of growing up (Latin immutabilis = unchangeable).
www.schwaene.koeln/immutabilis.html
It is considered likely that in historical times this colour morph was deliberately bred, especially in Eastern Europe, where this colour variant is particularly common, as there was a trade in swan skins for a time and the skins of the immutabilis morph were earlier marketable.
Unequal Siblings
Three of four cygnets of the mute swan family in the Floridsdorfer Waserpark.
Two cygnets aren't grey, as is the norm, but white. They are so-called ‘Polish swans’. This is a colour morph that hatches from the egg with white plumage and is therefore also known as ‘immutabilis swan’, as the colour of the plumage does not change in the course of growing up (Latin immutabilis = unchangeable).
www.schwaene.koeln/immutabilis.html
It is considered likely that in historical times this colour morph was deliberately bred, especially in Eastern Europe, where this colour variant is particularly common, as there was a trade in swan skins for a time and the skins of the immutabilis morph were earlier marketable.