Biology Reference
In-Depth Information
lished in their remote mountain domains, they evolved to expand their diets in response to
food sources available in their new homes, whether as fig eater, or bark chipper and grub
extractor, or spider hunter, or miner of specialized fruit hidden in woody capsules of ma-
hoganies and nutmegs. Some forms developed stronger legs to walk along tree branches and
pluck fruits and insects, for example, while others developed short, weak bills and special-
ized in soft fruits. To apply the founding principle of natural selection: those that diversified
in bill size or shape, and as a result fed more efficiently in their new habitat, invariably left
more surviving offspring, while other variants over time passed from the scene.
Although the honeyeaters of the South Pacific rarely receive mention in the textbooks, they
are another classic example of adaptive radiation in birds, with about 184 species descended
from a single ancestor. The wattled smoky honeyeater hanging about Bruce's camp represen-
ted one of the newest species in the family. As we saw earlier, some isolated species, such as
the Juan Fernández firecrown, remain rare, while a few, such as the green-backed firecrown,
become transplanted or jump the ecological barriers and become abundant and widespread.
Such shifts in rarity and abundance depend on a host of natural and human factors explored
in later chapters.
During his daily searches, Bruce had begun tallying the number of birds of paradise he
spotted or heard singing in the dawn chorus. By the second week in the Fojas, he had ob-
served in miniature the general pattern of distribution in New Guinea. Some species, such
as the two manucodes, the lesser and king birds of paradise, the riflebird, and the pale-billed
sicklebill, were confined to the lowlands and foothills of the Fojas. Other species, including
the bufftailed sicklebill and the several kinds of six-wired birds of paradise, restricted them-
selves to bands of forest at middle elevations. Still others, such as the black sicklebill that
Bruce heard on the first day, holed up only on mountaintops. So it turned out that over time
the birds of paradise had sorted by what biologists call altitudinal stratification. Perhaps some
species were better than others at taking advantage of what nature gave them at different elev-
ations and became further adapted to prospering in narrow elevational bands of forest. Above
or below their particular elevational band, they might have been replaced by another species.
As a group, birds of paradise have no rivals—except perhaps the pheasants—and are the
most beautiful birds in the world. There is widespread use of their plumage among New
Guinea natives, who fashion headdresses of the feathers to wear at clan gatherings. Some
clansmen prize the long enameled, pearly head feathers of the king of Saxony bird of para-
dise. Others go for the white, trailing plumes of the ribbon-tailed. Highly valued, too, are the
iridescent blue breast feathers of the superb bird of paradise. Beauty and extreme rarity in
New Guinea often coincide, with the result that some of these species have been wiped out
in areas around villages. A Papuan ornithologist documented the carnage wreaked by such
ornamentation, reckoning that about 36,000 birds had been killed to furnish headdresses for
one clan gathering in one mountain town.
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