Date: 10/2/19 9:47 pm
From: Brodie Cass Talbott <brodietlewis...>
Subject: [obol] Re: Pale Varied Thrush at Fields
As it happens, I was discussing just such a thrush at Portland Audubon with
a co-worker, who mentioned one reported to audubon, and shared this from
BNA:

"Aberrant plumages: Individuals lacking orange coloration have been
reported twice: a female was collected near Berkeley, CA, in 1921 (Law 1931
<https://birdsna.org/Species-Account/bna/species/varthr/references#REF49505>)
and an individual of unknown sex was observed in Cornwall, UK, in 1982 (Madge
et al. 1990
<https://birdsna.org/Species-Account/bna/species/varthr/references#REF35651>).
In both, areas that normally would appear ochraceous buff (orange) were
instead white. Distribution of melanistic coloration was not affected.
Close examination of individual collected near Berkeley revealed that crown
and nape were brown suffused with slate-gray, while back and rump were
slate-gray, very similar to coloration of an adult male. Based on these
observations, Law (Law 1931
<https://birdsna.org/Species-Account/bna/species/varthr/references#REF49505>)
speculated that brown coloration of upperparts of adult females is produced
by incorporation of lipochrome (orange) pigments into cortex of pennaceous
portions of feathers which, when combined with underlying melanistic
pigments, produces a brown coloration."

Cheers,
Brodie

 
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