The White-throated Sparrow (Zonotrichia albicollis) has two genetic
morphs, which are clearly distnguishable by color in alternate plumage,
but less distinguishable in basic plumage. To determine the
accuracy with which the morphs can be identificed in basic plumage in a
wintering population in North Carolina, we measured the brightness (extent
of pure white or black as opposed to tan or brown) in the median, lateral,
and superciliary strips of 279 birds of known age and sex and determined
each bird's morph after the prealternate molt in the spring.
Age, sex, and plumage all influenced the color of crown stripes in both
morphs. However, white morphs were significantly brighter than
tan morphs in all age- and sex-classes in basic plumage.
A simple formula based on a bird's age, sex, and brightnes of its median
and lateral stripes indentified tan and white morphs in basic plumage with
a success rate of 89%. In this wintering population, an estimated
61% of males and 49% of females were white morphs.