With regard to winged animals, such as birds, no creature is
liable to change of colour by reason of age, excepting the crane.
The wings of this bird are ash-coloured at first, but as it grows
old the wings get black. Again, owing to special climatic
influences, as when unusual frost prevails, a change is sometimes
observed to take place in birds whose plumage is of one uniform
colour; thus, birds that have dusky or downright black plumage turn
white or grey, as the raven, the sparrow, and the swallow; but no case
has ever yet been known of a change of colour from white to black.