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Aves
Evolution of birds
• evolved from a group of theropod dinosaurs (the
Jurassic period)
• The oldest known fossilArchaeopteryx
lithographica  has a mix of “reptilian” and avian
features.
• Reptilian: long tail, teeth, long clawed fingers
• Avian: feathers, ribs with uncinate processes, avian
shoulder girdle.
Archaeopteryx
(oldest known
fossil bird)
Jurassic
150mya
Characteristics of the birds
– Feathers a unique character among living animals,
but also found in dinosaurs.
– Endothermic
– Skeleton modified for flight. Bones hollow,
forelimbs support the wing, ribs with uncinate
processes, beak but no teeth, reduced tail.
– Breathing by lungs and associated air sacs
– Internal fertilization and hard-shelled amniotic egg
Endothermic
• Warm blooded
• Ability to generate heat & maintain a constant
body temperature
• Can live in hot or cold climates
• Requires more food
• Requires faster body processes to generate heat
Feathers:
•
Similar to reptilian scales (beta-keratin –
present in birds / reptiles)
• Retain scales on non-feathered parts
•
Dead structures; damage repair =
replacement
•
Specialized pockets of epidermal /
dermal cells (follicles)
Feathers appear in fossil record long before
flight (e.g., Caudipteryx
•
Hypotheses:
•
1) Insulation to retain heat (not
endothermic…)
2) Social interactions (e.g., reproduction)
3) Shading / insulation for eggs
Dinosaur feather impressions
Adaptations for Flight
Feathers
• Light weight & strong
• Branches coming off the
central shaft are called
barbs
• Barbs are connected across
the feather by smaller
branches called barbules
which hook into one
another
• Birds have different feathers
for different functions
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Feathers
Tail & Flight – Support during flight
Semiplume – Provides shape & color
Filoplume – Connected to nerve endings
Bristle – Around the eyes & mouth
Downy - Insulation
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Adaptations for Flight
• Body weight is further
reduced by reducing or
losing certain structures
and organs
–
–
–
–
–
No teeth
No urinary bladder
No penis
Only one ovary
Reduced large intestines
Yellow Warbler
(Dendroica petechia)
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Adaptations for Flight
• Highly efficient lungs able to
remove 31% of oxygen from
each breath vs. 24% in
humans
• Needed to sustain muscles
during flight
• Anterior & posterior air
sacks store air during each
breath
• During inhalation and
exhalation, fresh air is
passed across the lungs
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Specially Designed Skeletal System
• Birds have a blade-like sternum or breastbone
that the large muscles responsible for flight
attach to
sternum
• The skeletons of birds have several
adaptations that make them light, flexible,
but strong.
– The bones are honeycombed to reduce weight
without sacrificing much strength.
Flight - Wings are Specialized for
Particular Kinds of Flight
• Elliptical wings are good for maneuvering in forests.
• High speed wings are used by birds that feed during
flight or that make long migrations.
• Dynamic soaring wings are used by oceanic birds
that exploit the reliable sea winds.
• High lift wings are found in predators that carry
heavy loads. Soaring over land with variable air
currents.
Nervous System
• Birds have well
developed cerebral
hemispheres,
cerebellum
(important for
coordinating
movement &
balance), and optic
lobes.
Specially Designed Nervous System
• Most birds have very good eyesight
• Instead of moving their eyes in their head they
will move their whole head
Fig. 27.14
Vision
• Up to 8 times keener
than human vision
• Each eye moves
indendtantly
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Specially Designed Nervous System
• Usually have a poor sense of taste and smell
• Their sense of hearing is very good.
• Because of the need to distinguish between
the differences of different bird calls the bird
needs to be able to distinguish differences in
intensity and rapid fluctuations in pitch
Specially Designed Nervous System
• They have a third eyelid called a nictitating
membrane that is transparent and allows the
bird to blink to moisten its eyes in flight.
Respiratory System
• The highly adapted respiratory system of
birds is adapted for the high metabolic
demands of flight.
– The finest branches of the bronchi are
developed as tubelike parabronchi through
which air can flow continuously – instead of
ending in saclike alveoli as in mammals.
Respiratory System
• There is an extensive
system of nine
interconnecting air sacs
that connect to the
lungs.
• Air flows to the
posterior air sacs, to
the lung, then to the
anterior air sacs and
out.
• The result is that there
is an almost continuous
stream of oxygenated
air passing through the
highly vascularized
parabronchi.
Figure 27.12b
The one-way flow of air is achieved by using a system
of air sacs and a two breath cycle
19.10
Excretory System
• Urine is formed in large, paired
metanephric kidneys.
– There is no urinary bladder/sack, wastes dumped
into cloaca mixed with feces, forms white paste
with dark lumps
– Requires less water (not as toxic as urea)
– Nitrogenous wastes are secreted as uric acid
rather than urea.
– Bird kidneys can only concentrate solutes to 4-8
times that of blood concentration.
Excretory System
• Some birds,
including marine
birds, have a salt
gland to help rid the
body of excess salts.
– Salt solution is
excreted from the
nostrils.
– Concentrate salt 35X that in blood
Digestive System
Because birds lack teeth they can’t process food much
in the mouth so that is left up to the gastric system.
• Crop
– Storage
• Proventriculus
– Enzymes
• Gizzard
– Grind food
• Cloaca
– Waste
– Reproduction
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Bird’s digestive tract and other internal organs
http://www.dkimages.com/discover/previews/824/80016755.JPG
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Reproduction
Reproductive System
• testes very small  may enlarge 300 times at
the breeding season
• sperm  stored in a greatly enlarged seminal
vesicle.
• Males of most species lack a penis; mating
involves bringing cloacal surfaces in contact.
• In most birds, the left ovary and oviduct
develop and the right ovary and oviduct
degenerate.
Egg Production
• Infundibulum  The expanded end of the oviduct,
receives the discharged eggs.
• Special glands  add albumin to the egg as it passes
down the oviduct.
• Farther down the oviduct, the shell membrane, shell, and
shell pigments are also secreted.
• Fertilization  take place in the upper oviduct before
albumin and shell are added.
• Sperm remain alive in the oviduct for many days after a
single mating.
Fig. 27.25
Nesting and Care of Young
• Nearly all birds lay eggs that must be
incubated by one or both parents.
• Eggs of most songbirds require 14 days for
hatching; those of ducks and geese may
require a month.
• Often the female performs most of the duties
of incubation; rarely the male has equal or
sole duties.
Chicks
• Altricial
– No feathers
– Cannot walk or see
– Cannot feed themselves 
need parental care
– Nesting success in altricial
birds is very low;
sometimes barely 20% of
nests produce young.
Precocial
– Down feathers
– Can walk and see
– Can feed themselves
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Egg Shapes
Marine Birds
• Sea and shore provide a haven for
many species of birds.
• Birds that depend on the sea for
their survival are called Seabirds.
• There are nearly 9,000 species of
birds.
• Not all birds fly, but they all share
some important characteristics.
Marine Bird Adaptations
• True seabirds  have salt secreting
glands.
• Seabirds have webbed feet.
• Shore dwelling birds are not considered
seabirds.
• Seabirds require a land base on which
they can lay their eggs.
• Of the 9000 species of birds, only 350 are
true seabirds.
Most Common Marine Birds:
1. Albatrosses
2. Shearwaters and
Petrels
3. Frigatebirds
4. Boobies
5. Terns and Noddies
Penguins
• All 17 species of Penguin 
live in the southern
hemisphere.
• They are the best adapted
for swimming  their wings
have evolved to become
flippers.
• Penguins mate for life.
• The fathers hatch the chicks,
while the mothers leave in
search of food to bring back
to the chick.
• Penguins have adapted
special feathers to help them
withstand the cold waters,
and the freezing cold temps.
Did you Know ?
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Penguins can fly!!!!
Their average lifespan is 15-20 years.
Penguins have insulating layers of air, skin, and blubber.
Penguins like to slide across the ice on their big stomachs.
Most penguins can swim about 15 miles per hour.
There may be as many as 100 million penguins in the world.
Physical characteristics
• The emperor penguin  the largest
penguins, standing 3.7 ft and weighing
60-90 lbs.
• The smallest penguins fairy penguin,
standing just 16 in and weighing about
2.2 lbs.
• The penguin’s body is adapted for
swimming
•  streamlined and elongated body.
• tail I  short and wedge/flatted shaped,
• The legs and webbed feet are set far back on the
body, which causes penguins to stand upright
when on land.
• Wings  modified into paddle like flippers,
covered with short, scale-like feathers.
Penguin Habitat
• All 17 species live in the Southern
Hemisphere; on every continent.
• abundant on many temperate and
sub Antarctic islands.
• generally live on islands and remote
conditional regions  free from
land predators
• They are not only found in cold
climates such as Antarctica.
• a few species of penguin live so far
south. Several species live in the
temperate zone, and one species,
the Galapagos Penguin, live near the
equator.
Food
• feed  fish, squid, sardines, anchovies, but most of all, especially the
smaller penguins, on krill, a small shrimp  depend on food availability
• The location of prey can vary seasonally and even daily
• Various species  have slightly different food preferences.
• chinstraps forage for large krill .
• Emperors and kings primarily eat fishes and squids.
• Penguins primarily rely on their vision while hunting
• Penguins catch prey with their bills and swallow it whole while
swimming
• Penguins have a spiny tongue and powerful jaws to grip slippery prey
Reproduction
• On average, breeding does not begin until the fifth year, and
a few males do not breed until the eighth year
• Most species have an annual breeding season - spring
through summer
• The king penguin  has the longest breeding cycle  14 to
16 months. A female king penguin may produce a chick
twice in every three breeding seasons
• Both parents take turns incubating the egg. The incubation
period lasts from 4 weeks to 66 days.
• Depending on the species, penguins lay one to three eggs.
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