I first read about this form of mute swan a few years back, but have never come across one-until this week….. A few days away were had in Sussex, I was hoping to see the elegant tern, but was unsuccessful. A stroll along the beautiful Chichester canal reminded me somewhat of the Grantham canal. There it was, a mute swan family, two parents and three cygnets, two of them the more usual greyish colour and one an almost all white morph. Closer inspection revealed the paler colouration of the bare parts associated with this form, pinkish/grey beak and legs, (normally dark grey/black). In a couple of the photos this difference can be clearly seen. The following words are quoted from wildfowl expert Sebastien Reeber.
”No subspecies are recognised, but one colour morph known as the ‘Polish morph’, originally named Cygnus immutabilis Yarrell, 1838, and which is based on a form imported from coastal Poland to England. It is distinguished by the colour of immature plumages and the bare parts at all ages. This is an inherited mutation corresponding to leucism, encountered in all swans. It is very frequent in some populations of Mute Swan, especially where the species has been introduced, recently or not. Such populations descend from captive birds in which these characteristics were selected until the 19th century, in order to breed a domestic variant whose whiteness from an early age was more attractive”.