Strong beaks
The beak of Parrots is extremely strong; and well
adapted to the breaking open of nuts by sheer force. The mandible ends
in a transverse blunt edge, which presses against a corresponding horny
prominence of the upper beak. In the large Microglossa (cockatoo),
which lives on the stone-hard fruit of the kanari-tree (Canarium commune),
the
beak bears a striking resemblance to a sledge-hammer. Transverse ridges,
like those of a file, are common in front of the prominence of the upper
jaw, the bird using them as a rasp - no Parrot swallowing anything but
absolutely comminuted particles of hard substance, or pulpy and soft food
- and also for filing or sharpening its mandible.
In the SKIMMER, Rhynchops, the bill forms
two sharp vertical blades, which somewhat gape asunder, with the further
peculiarity that the mandibular sheath and the supporting bone itself is
considerably larger than the upper portion. A vertically compressed bill
is also common in the Alcidae, and is often vividly coloured during. the
summer. In the PUFFINS the outermost bright layers of the horny sheaths,
and the horny excrescences at the gape of the mouth and above the eyes
are cast off periodically, these parts being developed for the breeding
season (Bureau, Bull. Soc. Zool. France, 1877, p. 377 ff.)
Hornbills and Similar Protuberances
In many birds the covering of the bill, especially
near the base of the culmen and the forehead, is swollen, and forms various
protuberances, horns, knobs, and other apparently ornamental excrescences.
In the Coots and in Musophaga (PLANTAIN -EATER) the coating of the culmen
is produced backwards over the forehead, overlapping the latter as a conspicuous
white or yellow soft plate. Often the underlying bones, especially the
nasals and the adjoining premaxillary parts, are also swollen, and form
a light and extremely spongy meshwork of cancellated bony tissue, a peculiarity
which attains its highest development in the HORNBILLS and in the TOUCANS.
Similar swellings are the knobs on the bill or on the forehead of the SCOTER
and Mute SWAN, of Globicera among Pigeons, of certain Cracidae, and of
Macrocephalon (MEGAPODE). In most of these cases the swellings are very
light; rarely, as in the Helmet-HORNBILL, the bones of the forehead are
greatly enlarged, and, although much cancellated, of great weight and strength;
moreover, the horny epidermal covering of the forehead is three quarters
of an inch thick, and of the hardness and weight of ivory.
Crossbills and Wry bills
Another deviation is constantly found in the beak of the Crossbill, the sharply-pointed and hooked ends of the upper and lower jaws crossing
each other in an individually varying way, there being an equal number
of right and left-billed specimens. This crossing begins to show itself
before the young birds are fledged, increases with age, and ultimately
leads to an asymmetrical development of the masticatory muscles and of
the bones of the occipito-quadrate region.
In Anarhynchus frontalis (WRYBILL) the terminal
half of the bill is turned towards the right side, an abnormality which
exists in a marked degree even in the very young birds. The right edges
of the premaxilla and of the mandible are thin and strongly turned inwards,
so that the right and left sides are asymmetrical in section. The
left nostril and the groove which is continued towards the terminal third
of the bill remain in their original position, but the right nostril, and
still more the groove, are perceptibly slanting towards the right, as can
be ascertained by viewing the bill from the dorsal side.
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