Anomalous plumages: crows and others
I got a couple of shots of this guy in my yard. He has been around for several months. This one seems to have spots of his breast. Are there very many with markings like these? I have been in Oregon for over 30 years and I have never seen one before.
dlr
In reply to dlr & Tadduck, the occurrence of white or pale feathers in black crows occurs among many species or subspecies, but it may be limited to indviduals (a genetic aberration not shared with relatives) or a small part of a population (a transmitted genetic 'error'). For example, the Carrion Crows
Corvus corone on Wimbledon Common in west London for many years had white on the roots of their secondaries (Haven't been there since 2001). However, the curious pattern of distribution of black and grey-winged crows across Eurasia may not be attributable to just one control gene that normally ensures that plumage variation within a single population is not excessive, but also to additional genetic effects. hence, the appearance of a black-plumaged individual among a Hooded Crow
C. cornix 'grey crow' population may be due to the second effect where the control gene hasn't 'kicked in' (similarly grey-winged individuals in black-plumaged populations). I'm sure it will be much more complex than that, and subtly so!
However, many bird taxa display plumage changes while in captivity - Gouldian Finches, Budgerigars, show pigeons - a process that suggests that the operation of any control gene for plumage can be set aside or modified by 'nurture' differences, an almost Lamarckian suggestion. Also, the complexities of flamingo plumage colouring are far from fully explained.
I suggest that the above few examples may be the kind of context in which plumage 'oddities' can comfortably be placed, initially at any rate. It would be useful if somebody out there who really knows what they are talking about (unlike my selective examples) could enlighten us a little further!
MJB