What I have seen
twice, however, is an orange male House Finch. I have no idea what he is
eating, or where he is eating it, to account for the different coloration.
Does anyone know if this would have been the result of his summer diet?
This is caused by eating introduced honeysuckle.
I have seen it on finches, eye line on
White-throated sparrows (usually yellow), and
belly feathers of Veery as well as tips on waxwings.
Cedar Waxwings with orange instead of yellow tail
tips began appearing in the northeastern United
States and southeastern Canada beginning in the
1960s. The orange color is the result of a red
pigment picked up from the berries of an
introduced species of honeysuckle. If a waxwing
eats the berries while it is growing a tail
feather, the tip of the feather will be orange.
From the Birds of North America account for house finch:
Yellow/orange/red color of feathers results from
deposition of 3 carotenoid pigments: ß-carotene,
which produces yellow to orange color in
feathers; isocryptoxanthin, which produces orange
color in feathers; and echinenone, which produces
red color in feathers (Brush and Power 1976).
Controlled feeding experiments with captive House
Finches indicate that all individuals in all
populations have same potential to be brightly or
drably plumaged; variation in color of feathers
reflects differential access to carotenoid
pigments at the time of molt (Brush and Power
1976, Hill 1992, in press a, b). Males from 4
different C. m. frontalis populations (brightly
plumaged Michigan, California; drably plumaged
California, Hawaii) responded to standardized
diets in a similar manner. When they were fed a
plain seed diet, which was fully nutritious but
provides few carotenoid pigments, all males grew
feathers with similar pale yellow coloration
(Brush and Power 1976, Hill 1992, in press a). On
a seed diet with ß-carotene added, all males grew
pale orange feathers. And, on a seed diet with
the red carotenoid canthaxanthin added, all males
grew bright red feathers. Moreover, the variance
in plumage coloration among males after treatment
on a standardized diet was significantly lower
than the variance in appearance among males from
wild populations (Hill 1992). Female House
Finches also converged on a similar plumage when
their access to carotenoid pigments was
standardized during molt (Hill in press b).
Although relatively few wild females show
detectable carotenoid pigmentation (see
Distinguishing Characteristics), when
canthaxanthin was added to their diets all
females showed maximum female expression of
carotenoids with a red wash on the rump, crown,
and underside (Hill in press b).
Hope this helps.