Biology
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31-2 Birds
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31-2 Birds
What Is a Bird?
What Is a Bird?
Birds are reptilelike animals that maintain
a constant internal body temperature.
Birds have an outer covering of feathers;
two legs that are covered with scales and
are used for walking or perching; and
front limbs modified into wings.
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What Is a Bird?
Feathers are made mostly of protein and develop
from pits in the birds' skin.
Feathers help birds fly and also keep them warm.
The two main types of feathers are contour and
down.
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What Is a Bird?
Feathers
Barb
Contour feather: Contour
feathers provide the lifting force
and balance needed for flight.
Down feather: Down
feathers trap air close to the
body and keep the bird warm.
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Barbule: The hooks on
each barbule fit together,
holding them flat.
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Evolution of Birds
Evolution of Birds
Paleontologists agree that birds evolved from
extinct reptiles.
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Embryos of birds and reptiles develop within
amniotic eggs.
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Both excrete nitrogenous wastes as uric acid.
Bones that support the limbs, and other
skeleton parts, are similar in both groups.
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Evolution of Birds
Archaeopteryx was the first birdlike fossil discovered.
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Archaeopteryx looked like a dinosaur, but it had
feathers.
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It had teeth in its beak, a bony tail, and toes and
claws on its wings.
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It may be a transitional species between
dinosaurs and birds.
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Evolution of Birds
Other fossil evidence leads some to hypothesize that
birds and dinosaurs both evolved from an earlier
common ancestor.
The origin of birds is still not completely resolved.
New fossils of ancient birds are being found all the
time.
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Evolution of Birds
Evolution of Birds
Dinosaurs
Modern reptiles
Modern birds
Saurischia
(lizard-hipped
dinosaurs)
Ornithischia
(bird-hipped
dinosaurs)
Archaeopteryx
Ancestor of
dinosaurs
Reptile ancestor
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Form, Function, and Flight
Form, Function, and Flight
Birds have a number of adaptations that
enable them to fly, including:
• highly efficient digestive, respiratory, and
circulatory systems
• aerodynamic feathers and wings
• strong, lightweight bones
• strong chest muscles
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Form, Function, and Flight
Body Temperature Control
Birds generate their own body heat and are called
endotherms.
Endotherms have a high rate of metabolism.
Metabolism produces heat.
Feathers insulate a bird enough to conserve most
of its metabolic energy, allowing it to keep warm.
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31-2 Birds
Form, Function, and Flight
Esophagus
Crop
When a bird eats,
food moves down
the esophagus and
is stored in the crop.
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Form, Function, and Flight
First chamber of stomach
Gizzard
Moistened food passes
to the stomach, a twopart chamber.
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Form, Function, and Flight
Small intestine
Large intestine
As digestion
continues, the food
moves through the
intestines.
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31-2 Birds
Form, Function, and Flight
Cloaca
Undigested food is
expelled through
the cloaca
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Form, Function, and Flight
Air flows in a single direction.
The one-way flow of air:
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constantly exposes the lungs to oxygen-rich air.
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maintains a high metabolic rate.
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provides efficient extraction of oxygen, which
enables birds to fly at high altitudes where the
air is thin.
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Form, Function, and Flight
Excretion
Excretion in birds is similar to that of most living
reptiles.
Nitrogenous wastes are removed from the blood
by the kidneys, converted to uric acid, and
deposited in the cloaca.
Most of the water is reabsorbed, leaving uric acid
crystals in a white, pasty form.
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Form, Function, and Flight
Skeletal System
of a Bird
Vertebra
Skull
Collarbone
(wishbone)
Pelvic girdle
Strut
Tailbone
Pectoral griddle
Air
space
Sternum
Rib cage
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Form, Function, and Flight
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Bones are
strengthened by struts.
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Air spaces make bones
lightweight.
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31-2
Click to Launch:
Continue to:
- or -
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A bird with a short, thick bill probably eats
a. fish.
b. seeds.
c. insects.
d. fleshy fruit.
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Archaeopteryx has characteristics of both
a. modern birds and ancient birds.
b. amphibians and reptiles.
c. reptiles and modern birds.
d. amphibians and modern birds.
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31-2
Which of the following bird adaptations is NOT
associated with flight?
a. bones with many hollow air spaces
b. air sacs in addition to lungs
c. gizzard
d. contour feathers
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31-2
Which of the following birds assists in pollinating
flowering plants?
a. pelican
b. hummingbird
c. raptor
d. heron
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