Figure 13 in The dark side of birds: melanism-facts and fiction

Figure 13. Gould's Chestnut-coloured Partridge Ortyx castanea, which was a melanistic Northern Bobwhite Colinus virginianus; the normal black head markings have overrun their boundaries, whilst the rest of the plumage is darker as well, the latter mainly due to increased phaeomelanin hence 'Chestnut-coloured' (Hein van Grouw, © Natural History Museum, London)