The projecting jaws of a bird, with their
horny sheath, are called bills, beaks, or
technically, the rostrum.
Birds have no teeth but they can
definitely cut food, break seeds and nuts,
extract food from hard to reach places and
much more. The horny covering of both the
upper and lower mandible is known as the
rhamphotheca. Bill shape is very important
to the bird for obtaining its preferred food
(and to us in identifying them).
In the bird world it is uncommon for bills
of males and females of the same species
to be significantly different (sexual dimorphism).
However, a few Utah birds do display sexual
dimorphism. Male and female American Avocets
can be identified with some degree of accuracy
by how much the recurved bill curves upward
-- more upturned in the female. Can you guess
why the scientific name of the American Avocet
is Recurvirostra americana? Another example
is the White Pelican where males grow an
erect horny plate on the top of the bill
during breeding season.
By understanding the adaptations of the bill
in relation to a bird's feeding habits, birders
can easily place birds into groups to facilitate
identification. The long pointed bills of
herons and egrets are designed to seize fast
moving prey in shallow water and reeds. A
more perfected bill for grasping fish in
open water is the bill of the merganser,
with its saw-tooth-like lateral cutting edges
(tomia). The elongated, slender bills of
most wading birds (shorebirds) are adapted
to probing for food in mud or sand. We could
go on and on -- the "toothed" raptorial
bill of the falcon for tearing meat, the
small pointed bill of warblers for gleaning
insects, the conical bill of sparrows and
finches for cracking seeds, long needle-like
bills of hummingbirds for reaching nectar
in flowers, and even the Red Crossbill with
offset mandibles designed to pry seeds from
conifer cones.
Look in your bird identification guide and
see if you can guess the feeding habits of
a bird just by looking at the shape and size
of the bill.
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