Everything about Beak totally explained
The
beak,
bill or
rostrum is an external anatomical structure of
birds which, in addition to eating, is used for
grooming, manipulating objects, killing prey, probing for food,
courtship and feeding their young. The term also refers to a similar mouthpart in some
cephalopods,
cetaceans,
turtles,
Anuran tadpoles and
sirens.
Anatomy
Beaks can vary significantly in size and shape from species to species. The beak is composed of an upper jaw called the
maxilla, and a lower jaw called the
mandible. The jaw is made of bone, typically hollow or porous to conserve weight for flying. The outside surface of the beak is covered by a thin horny sheath of
keratin called the
rhamphotheca. Between the hard outer layer and the bone is a vascular layer containing
blood vessels and nerve endings. The rhamphotheca also includes the
knob which is found above the beak of some swans, such as the
Mute Swan, and some
domesticated Chinese geese (
pictured).
The beak has two holes called
nares (
nostrils) which connect to the hollow inner beak and thence to the
respiratory system. The nares are usually located directly above the beak. In some birds, they're located in a fleshy, often waxy structure at the base of the beak called the
cere (from
Latin cera).
Hawks,
parrots,
doves,
skuas and
budgerigars are among the birds that have ceres. Budgerigars are
dimorphic in that the males' ceres turn bright blue upon maturity, while the females' ceres turn tan. The female budgies' ceres also appear wrinkled, to a greater extent during periods of fertility. Immature budgies have pale pinkish ceres which are smooth and shiny.
On some birds, the tip of the beak is hard, dead tissue used for heavy-duty tasks such as cracking nuts or killing prey. On other birds, such as ducks, the tip of the bill is sensitive and contains nerves, for locating things by touch. The beak is worn down by use, so it grows continuously throughout the bird's life.
Unlike jaws with teeth, beaks are not used for chewing. Birds swallow their food whole, which is broken up in the
gizzard.
Examples of birds with unusual beaks include the
hummingbird, the
toucan and the
spoonbill.
In the
mallard, and perhaps in other
ducks, there's no cere, and the nostrils are in the hard part of the beak, as a soft cere would be liable to injury when the duck dredges for food among submerged debris and stones.
Billing
During courtship, mated pairs of a variety of bird species touch and clasp each other's bills. This is called
billing, and appears to strengthen the
pair bond (Terres, 1980).
Gannets raise their bills high and repeatedly clatter them (
pictured); the male
puffin nibbles at the female's beak; the male
waxwing puts his bill in the female's mouth; and
ravens hold each other's beaks in a prolonged "kiss".
Terminology
The term
decurved refers to a downward curving beak.
Further Information
Get more info on 'Beak'.
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