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Birds
Section 31.2
Animal Classification
Invertebrates
Sponges
Cnidarians
Worms
Mollusks
Arthropods
Echinoderms
- Class Aves
Animals
Ectotherms
(cold-blooded)
Vertebrates
Endotherms
(warm-blooded)
Fishes
Amphibians
Reptiles
Birds
Mammals
What is a Bird?
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Class Aves
Birds inhabit a variety of environments
around the world including Antarctica,
deserts, and tropical rain forests
What is a Bird?
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Birds are known as
feathered dinosaurs
Birds evolved from
small, two-legged
dinosaurs called
theropods
Like reptiles, birds have
clawed toes and protein
scales on their feet
Theropod
Ar·chae·op·ter·yx
Archaeopteryx
“ancient wing”
What is a Bird?

Although some birds are flightless, all birds
have feathers and wings
Cassowary
Kiwi
Emperor Penguins
Feathers
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Feather – a lightweight, modified protein
scale that provides insulation and enables
flight
Preening – the process of birds cleaning its
feathers
Feathers

During preening, a bird also uses its bill or
beak to rub oil from a gland near the tail onto
the feathers

This helps feathers last longer
Feathers
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Even with good care,
feathers wear out and
must be replaced
Molting – the shedding
of old feathers and the
growth of new ones
Most birds molt in late
summer
Feathers
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Most birds do not lose their feathers all at
once and are able to fly while they are
molting
Wing and tail feathers are usually lost in pairs
so that the bird can maintain its balance and
flight
Feathers
Contour
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Contour feather – used
for flight
Down feather – used
for insulation
Barbs – interlocking
sections on feathers
Down
Shaft
Feathers
Feathers
Feathers

Coverts – The small feathers that cover the
base of other feathers on a bird’s body,
thereby filling in the plumage
Feathers

Alula – A bird’s “thumb”; small stiff feathers
on the 1st digit of a bird's wing
Feathers

Flight feathers of the
wings
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Primaries
Secondaries
Tertiaries
Tail feathers

Rectrices
Feathers
Rectrices –
Light blue
Skeletal
System
cranium
maxilla
mandible
sternum
humerus
carpals
metacarpals
Skeletal
System
alula
Metacarpals
Metacarpals
Humerus
Wings

Sternum – breastbone

Powerful flight muscles are attached to the
sternum and to the upper bone of each wing
How do Birds Fly?
Flight Requires Energy

A bird’s four-chambered, rapidly beating
heart moves oxygenated blood quickly
throughout the body
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A chickadee’s heart beats 1000 times a minute
A human’s heart beats 70 times a minute at rest
Flight Requires Energy
Flight Requires Energy
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A bird’s respiratory system supplies
oxygenated air to the lungs when it inhales as
well as when it exhales
A bird’s respiratory system consists of lungs
and anterior and posterior air sacs
Flight Requires Energy
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During inhalation, oxygenated air passes
through the trachea (windpipe) and into the
lungs
Most of the air passes directly into the
posterior air sacs
Flight Requires Energy

When a bird exhales deoxygenated air from
the lungs, oxygenated air returns to the lungs
from the posterior air sacs
Flight Requires Energy
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At the next inhalation, deoxygenated air in
the lungs passes into the anterior air sacs
Flight Requires Energy

Finally, at the next exhalation, air passes
from the anterior air sacs out of the trachea
1.
2.
3.
4.
Endotherms

Endotherm – an animal that maintains a
nearly constant body temperature that is not
dependent on the environmental temperature
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Birds are able to maintain the high energy levels
needed for flight because they are endotherms
Endotherms
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Feathers reduce heat loss in cold
temperatures

The feathers fluff up and trap a layer of air that
limits the amount of heat lost
Endotherms
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Responses to high temperatures include
flattening the feathers and holding the wings
away from the body
Birds also pant to increase respiratory heat
loss
Endotherms
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Birds and other endotherms must eat large
amounts of food to sustain these higher
levels of energy

Endotherms have higher metabolisms than
ectotherms
Obtaining Food

There’s a direct relationship between a bird's
beak and its ability to find food and survive in
a given environment
Internal Anatomy
Internal Anatomy
Reproduction
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Fertilization is internal and shelled amniotic
eggs are produced in birds and reptiles
All females have cloacas whereas most
males have cloacas
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During copulation (mating), a male and female
align their cloacas so sperm can enter the female
Reproduction
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A small amount of male birds have phalluses
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Examples: ducks, chickens, and ostriches
Ducks are evil…
Birds eggs are encased in a hard shell, unlike
the leathery shell of a reptile
Ostrich Mating Ritual
http://www.youtube.com/watch?v=McunSYwfcoI
Reproduction
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Incubate – birds sit on their eggs to keep
them warm
The eggs are turned periodically so that they
develop properly
Reproduction
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In some species, both parents take turns
incubating eggs; in others, only one does so