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Wetmore, Alexander, 1886-, et al. / Warm-blooded vertebrates

Chapter III: color and its arrangement,   pp. 25-38 PDF (5.6 MB)

Page 31

Similarly, only the exposed tips of the feathers of the back
are brownish or buffy white, while the bases are jet-black.
As spring advances the tips of the feathers wear away,
leaving the head and rump white and the back completely
black, producing an astounding alteration in appearance.
A comparison of unworn and worn feathers serves easily
to demonstrate what has happened (Plate iO). A change
of similar kind may be observed without difficulty in the
male English sparrow, whose dark throat patch becomes
in the fall much obscured by grayish tips on the feathers.
As the breeding season approaches these light tips wear
away, leaving the black marking fully exposed and con-
siderably altering the appearance of the bird.
Some species of waterfowl, particularly ducks, snow
and blue geese, loons, and phalaropes at times may ex-
hibit abnormal reddish or reddish-brown stains. These
are most common on the head and undersurface, and
result from the deposition of iron as ferric oxide on the
outside of the feather. In the shallow pools of the tundras
of the far north, and in many ponds in other regions, the
bottom mud is frequently covered with a bright reddish-
brown deposit of this same ferric oxide. We can easily
understand how water birds swimming and feeding in these
waters would be stained with this material. The iron is
tenacious and adheres permanently, so that only a molt
can free the bird of the stain.
The natives of some parts of Brazil produce an abnormal
coloring in parrots and other cage birds by rubbing their
heads, during the time when new feathers are being grown,
with a secretion from the skin of a toad. This treatment
changes green feathers to yellow. The birds thus modified
retain this peculiarity of plumage until the next molt, and
are known as contrafeitos or counterfeits.
A more common artificial color change consists in the
production of orange-colored canaries, a species in which
the yellow tint is due to a fatty pigment. The method
was discovered by certain breeders of canaries, who for a
[3I I

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