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

Chapter I: birds in relation to man,   pp. 1-12 PDF (4.2 MB)

Page 1

WE have only to consider the great ostrich, with its two-
toed feet and flightless wings, and the tiny humming
birds (some of which are smaller than the larger insects),
with bodies highly specialized for flight, to realize some-
thing of the complexity of that class of animals called birds.
Yet in spite of the diversity indicated by these two ex-
tremes, the various birds betray remarkable uniformity in
their structure and have many characters in common.
They all have, for example, a body covering of feathers,
a characteristic which instantly differentiates them from
all other vertebrated animals. Though feathers may vary
from soft, fluffy downs and graceful plumes to stiffened
quills that give to wings the supporting surface essential
to flight, yet as a body covering they are so characteristic
that we can always identify theni and so assign the most
peculiar of birds to its proper class. For practical pur-
poses, therefore, it is sufficient to define birds as warm-
blooded animals with a body covering of feathers.
Birds as a group have attained almost universal distri-
bution over the earth, thanks to their ability to fly and to
their many specializations of form, which permit them to
maintain a continuous existence over or on both land and
water. As a result of these adaptations to varied environ-
ment some type of bird may be found at some season of
the year everywhere in the world, with the possible ex-
ception of the central part of the vast Antarctic continent,
which is not yet thoroughly explored. Even the broad
areas of ocean furnish a home to peculiar avian species at

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