Leucism and Leusistic. Yep, this is our word for today, and illustrated by a very cool bird I found in Mai Po, in late 2020. Yes, this is a Red Whiskered or crested Bulbul.
See the "normal" picture at the end below....
Bird Leucism: ooook, you ready? this is a genetic mutation that results in a total or more frequently partial reduction of colour in a bird's feathers/plumage. This reduction of colour is due to an inadequate deposition or fixation of pigments only in the bird's feathers. Other parts of the bird's body have normal coloration. so, we have this wonderful black and white crest, with the red-whiskers still present.
Five more interesting (not to say fascinating) facts about colours in birds:-
It is genetics that determine true albino birds: Both parents have to carry the uncommon recessive genes that produce rare pure white offspring. For more on albinos see 4.
A pied or piebald bird’s leucistic feathers are rarely in a symmetrical pattern; like in the example above. its chaos in the crest.
Typically, leucism affects only dark feathers, so some birds with leucism have white feathers while still maintaining the bright colours of other feathers - like the red whiskers.
A bird is a true albino if its feet, legs, bill, and eyes are pale pink or red.
Birds with discolouration may be lonely...as they may struggle during courtship. Many birds use plumage colour as a way to find and recognise potential mates. so spare a thought for this individual above, but it was in a flock, so had company.
And here the normal colouration of this bird: