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Wetmore, Alexander, 1886-, et al. / Warm-blooded vertebrates
(1931)

Chapter II: adaptations for progression by flying ,   pp. 13-24 ff. PDF (4.7 MB)


Page 21


ADAPTATIONS FOR PROGRESSION BY FLYING
delicate enough to be subject to wear and must be re-
newed at regular intervals, usually once each year when
the bird molts. In molt the worn feathers become
loosened in their sheaths and drop out, and a new feather
germ, which has been forming in the feather follicle at the
FIG. 3. The arrangement of the feather tracts in the gartered
trogon (Chrysotrogon caligatus). Drawn by Alexander Wetmore
base of or beside the old feather, develops into a new
structure in exact imitation of the original growth. This
annual shedding usually follows the breeding season. At
this time adult birds, in very worn dress, become dull and
quiet, cease singing, and retreat to sheltered places where
they, are not easily seen. Young may be molting at the
same time; in most birds the first plumage grown by the
young during the early weeks of life is evanescent, and
gives way almost immediately after growth to an adult
dress, usually of a different color from the nestling dress.
[211]


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