In the numerous
tree-creeping groups, which, seem as unrelated to the oven-bird as the
woodpecker is to the hoopoe, we find a score of wonderfully different
forms of beak; but many of them retain the probing character, and are
actually used to probe in rotten wood on trees, and to explore the holes
and deep crevices in the trunk. We have also seen that some of these
tree-creepers revert to the ancestral habit (if I may so call it) of
seeking their food by probing in the soil. In others, like Dendrornis,
in which the beak has lost this character, and is used to dig in the
wood or to strip off the bark, it has not been highly specialized, and,
compared with the woodpecker's beak, is a very imperfect organ,
considering the purpose for which it is used. Yet, on the principle that
"similar functional requirements frequently lead to the development of
similar structures in animals which are otherwise very distinct"--as we
see in the tubular tongue in honey-eaters and humming birds--we might
have expected to find in the Dendrocolaptidae a better imitation of the
woodpecker in so variable an organ as the beak, if not in the tongue.
Probably the oven-birds, and their nearest relations--generalized,
hardy, builders of strong nests, and prolific--represent the parental
form; and when birds of this type had spread over the entire continent
they became in different districts frequenters of marshes, forests,
thickets and savannas.
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