White black swan (4/11)

An unusual white black swan. There are many causes of anomalous white colouration in birds which are difficult at best to diagnose from a distance. This swan may have progressive greying or be partially leucistic –two conditions that are particularly difficult to distinguish in the field. Leucism occurs when a bird produces melanin (unlike albinos) but the pigment is not correctly deposited in some or all feathers and is less common than progressive greying.