Unequal Siblings
One of these two juvenile mute swans isn't grey, as is the norm, but white. It's a so-called 'Polish Swan'. 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. de.wikipedia.org/wiki/H%c3%b6ckerschwan
In the background you can see the young siblings of a greylag goose family. During the breeding season, there was a war between the greylag goose and mute swan parents. Now, however, both families peacefully share the shade under this weeping willow in the Floridsdorfer Wasserpark in Vienna. flic.kr/p/2qXDtgF
Unequal Siblings
One of these two juvenile mute swans isn't grey, as is the norm, but white. It's a so-called 'Polish Swan'. 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. de.wikipedia.org/wiki/H%c3%b6ckerschwan
In the background you can see the young siblings of a greylag goose family. During the breeding season, there was a war between the greylag goose and mute swan parents. Now, however, both families peacefully share the shade under this weeping willow in the Floridsdorfer Wasserpark in Vienna. flic.kr/p/2qXDtgF