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Birds
Characteristics of Birds
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The following characteristics distinguish
birds from other Vertebrates:
Forelimbs modified into wings
 Feathers
 Hollow, lightweight bones
 Endothermic
 Efficient respiration
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Characteristics of Birds cont.
4 chambered heart
 The two hind limbs, with clawed toes
support body and scaly feet
 A toothless, horny break in present
 Amniote eggs are encased in hard,
calcium-containing shells.
 Furculum (wishbone)
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Class Aves – Birds
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Ornithology – study of birds
Feathers!
Soft, fluffy down feathers
cover body of nestling birds
and provide and insulating
undercoat for adults.
 Contour feathers cover the
head and body and provide
coloration
 Flight feathers are
specialized contour feathers
on the wings and tails and
they provide lift
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Feathers Continued
At maturity each vane
(branch of feather) has many
barbules that are equipped
with microscopic hooks to keep
feathers together
 Birds preen, or comb through their
feathers spreading oils to keep them
waterproof and repairing vanes
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Oil is secreted from a preen gland
Feathers
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Most birds go through a major molt,
during which the birds replaces its flight
feathers
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This occurs in the late summer between
breeding and migration.
Endotherms
Generate and regulate body heat
internally
 Enables birds to inhabit both cold and
hot climates
 Body temperature ranges from 40-46
degrees Celsius.
 To help conserve body heat, birds fluff
out their feathers to insulation.
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Beaks and feet
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Hawks and eagles have
powerful break and clawed
talons that help them
capture and then rip their
prey.
Swifts have a tiny breaks
that opens wide like a
catcher’s mitt to share
insects in midair.
The feet of flightless birds,
on the other hand are
modified for walking and
running
Beaks
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Short and thick - seed cracking (robin)
Long and thin, slightly curved - eating nectar
(hummingbird)
Strong, chisel like - drilling (woodpecker)
Sharp, curved and pointed - tearing flesh (hawk)
Long and flattened - straining algae and plants
(ducks)
Spear shaped - spearing fish (heron)
Feet
3 toes in front, 1 behind - perching (robin)
 2 toes in front, 2 behind - climbing (parrot)
 Powerful curved talons - grasping prey
(hawk)
 Webbed - swimming (duck)
 Long and thin - wading (heron)
 Thick and stout - running (ostrich)
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copyright cmassengale
Skeletons and Muscles
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Combine lightness and strength
Bones are thin and hollow
(internal struts to add strength)
Many large bones are fused:
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Collar bone into wishbone
Pelvic girdle
Parts of the vertebra
Fusion of bones helps provide a
rigid frame for flight
Have very large pectoral muscles
and sternum modified into keel
Digestive System
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Food passes from the mouth
cavity straight to the
esophagus.
Enlargement of the
esophagus called the crop
stores and moistens food.
In the first chamber of the
stomach, gastric fluids begin
breaking down the food.
Then food passes through the
gizzard, a muscular organ
that kneads and crushes the
food
Excretory System
The avian excretory system is also efficient
and light weight
 The two kidneys filter a nitrogenous waste
called uric acid from the blood
 highly concentrated uric acid travels by
ducts called ureters to the cloaca, where
along with undigested matter from the
intestines, it is excreted in a semisolid,
usually white mass
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Respiratory System
Air enters through
paired nostrils at base
of beak
 When bird exhales
the carbon dioxiderich air from the
lungs, oxygen rich air
is forced out of the
posterior air sacs into
lungs via small air
tubes
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Circulatory System
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4 chambered heart
Right and left sides completely separated
Right side receives deoxygenated blood from
the body and pumps it to the lungs
Left side receives oxygenated blood from the
lungs and pumps it to the rest of the body
Has a single aortic arch
Most birds have a rapid heart beat compared to
other vertebrates – Hummingbird (600 times a
minute)
Nervous System
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Birds have a large brains, relative to their size
Cerebellum coordinates movement
Cerebrum controls complex behavior patterns such as
navigation, mating, and nest building
Optic lobe receives and interpret visual stimuli
Keen vision is necessary for taking off, landing,
spotting landmarks, hunting and feeding
Have good color vision
Birds large eyes are located near the sides of its
head, giving a bird a wide field of vision
Nervous system
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Birds large eyes are located near the sides of its head,
giving a bird a wide field of vision
Birds with eyes near the front of the head have better
binocular vision
Hearing important to nocturnal species that rely on
sounds to help them locate prey
Birds lack internal ears-ear canal leads to a tympanic
membrane, called an eardrum
Sense of smell is poorly developed except in ducks and
flightless birds
Sense of taste helps birds avoid bitter-tasting or toxic
foods
Reproductive System
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Bird sperm is produced in two
testes that lie beneath the
kidneys
Sperm passes through small
tubes called the vas deferens
into the male’s cloaca
During mating the male presses
his cloaca to the females and
releases sperm
Females single ovary releases
eggs into a long, funnel-shaped
oviduct where they are fertilized
by sperm
Reproductive System
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Fertilized eggs move down the oviduct, where they
receive protective covering and a shell
Unfertilized egg consists of a nucleus, cytoplasm, and
a yolk
When fertilized, the embryo is suspended in
albumen, the egg white
The liquid medium is supported by ropelike strands of
material called chalaza that are attached to the shell
membrane
Female has a shell gland that secretes a protective
calcium carbonate shell to surround the egg
Incubation and Development
A female bird usually lays
eggs in the nest. One or both
parents will incubate or warm
the eggs by sitting on them.
 They cover them with a thick,
featherless patch of skin on
their abdomen called a brood
patch.
 In penguins the male emperor
heats the egg by placing it on
his webbed feet and enfolding
it with his warm abdomen.
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Incubation and Development
Embryo development
begins when the zygote
forms a plate of cells on
the surface of the yolk.
 This plate begins to
form the tissues and
organs
 The membrane
produces digestive
enzymes that dissolve
proteins and lipids in
the yolk.
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Incubation and Development
Blood vessels in the yolk sac membrane
carry the nutrients to the embryo.
 When hatching begins the embryo
makes a star-shaped crack in the shell
with a scale-like egg tooth.
 The chick presses and scrapes the shell
until the crack widens enough for the
chick to emerge.
 The egg tooth falls off soon after the
chick hatches.
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Incubation and Development
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Bird have two
contrasting methods for
rearing young:
Those that lay many eggs
and incubate them for
long periods hatch
precocial young.
 These birds are active as
soon as they hatch, they
can walk, swim, and feed
themselves. For examples
ducks and quail.
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Incubation and Development
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Birds that lay only a few eggs and hatch
quickly produce altrical young.
They depend on both parents for several
weeks.
 For ex. Woodpeckers, hawks, pigeons
parrots.
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Behavior
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The long periods of parental care
may enable birds to learn such
complex behaviors as courtship,
nesting, and migration.
Young birds need protection until
they develop the strength to fly and
obtain food
Territoriality and Courtship
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During the breeding season many male birds
establish an area that they defend against other
males of their species – territorial
The male then attempts to attract a female to share
this territory.
Once a territory is established most birds engage in
a period of courtship, behavior that is designed to
attract a mate.
Many males attract females by means of their
brightly colored feathers.
Some males combine song with flight displays.
Nest Building
Nests hold eggs, conceal young birds
from predators, provide shelter from
the elements, and sometimes even
serve to attract a mate.
 Most birds build nests in sheltered,
well-hidden spots- from holes in the
ground to treetops.
 As a further adaptation to their
environment, birds construct their
nests of almost any material available.
 Twigs, grasses, feathers, and mud are
the most common materials used.
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Migration
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When temperatures drop
and the food supply
dwindles, many birds
migrate to warmer climates.
Birds rely on a variety of
cues to help them navigate.
Some species monitor the
position of the stars or the
sun.
Others rely on topographical
landmarks, such as
mountains.
Migration
Magnetic cues, changes in air pressure,
and low –frequency sounds may also
provide information to migrating birds.
 The ability of birds to read these cues,
along with their many adaptations for
flight, enables them to migrate to and
inhibit virtually any environment.
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Evolution and Classification
Almost every feature of their reptilian
anatomy has undergone modification in
their adaptation to flight.
 Becoming endotherms has enabled
birds to survive in virtually every
known environment
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Class Aves – Birds
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Birds are found in most every habitat
from forests to deserts, even in caves.
Some birds dive in the ocean to 45 m to
catch prey.
 Birds live at both the North & South poles.
 The bee hummingbird of Cuba weighs 1.8g
and is one of the smallest vertebrate
endotherms.
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Origin and Early Evolution
Evidence from fossils
and from studies of
comparative anatomy
indicates that birds
evolved from reptiles
 Their features and their
fragile hollow bones do
not preserve well 
not very many fossils
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Classification
Most taxonomists classify
the nearly 9,000 species
of Class Aves into 27
orders
 Birds are classified by
their beaks and feet
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Bird Groups
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Bird species are often categorized into six
groups based on the bird’s lifestyle
Perching birds
 Birds of prey
 Flightless birds
 Water birds
 Wading birds
 Diving birds
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Terrestrial (land) Birds
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Most perching birds, birds of prey,
and flightless birds are terrestrial
birds
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They live mainly on dry land
Terrestrial birds have feet adapted to
running, perching, or hunting and beaks
adapted to eating fruits, seed, insects,
or small animals
Perching Birds
Are the most common group of birds
 In order to perch and grip onto branches:
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One toe points backwards
 All other toes point forwards
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The beaks of perching birds are:
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Strong for cracking open seeds and nuts
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Ex. Goldfinches
Long thin beaks for catching insects in the air
or digging them out of the ground or tree
trunks
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Ex. Warbler
Birds of Prey
Most Birds of prey are hunters with
keen vision
 Eagles, hawks, and smaller birds of prey
hunt during the day
 Owls have huge eyes and hunt for small
prey during the night
 Some birds do not use vision to hunt
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Vultures rely on their incredible
sense of smell to find dead animals
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Birds of Prey
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Most birds of prey have sharp talons and
curved beaks
Talons are used to grasp prey
 Curved beaks are used for tearing flesh
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Most birds of prey hunt alone
 However, some birds of prey hunt in
groups and flush prey towards their
waiting partners
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Flightless Birds
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Flightless birds are the largest
birds
The biggest flightless birds are ostriches,
emus, rheas, and cassowaries
 There are some small flightless birds
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Example: Flightless Kiwi is the size of
a chicken
They have small wings and are
built to run on land
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Ostriches can run up to 55 km/h
Flightless Bird Legs
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Many flightless birds have long, strong
legs
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Ostriches have two large, clawed toes on
each foot
Aquatic Birds
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Diving birds, water birds, and
wading birds are aquatic birds
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Live mainly in water
Aquatic birds have feet adapted to
paddling and wading
 Aquatic birds have beaks adapted to
eating aquatic organisms
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Diving Birds
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Not all flightless birds live on land
Penguins are flightless, and their wings and feet
have been adapted for swimming
 All 17 species of penguins live in the Southern
Hemisphere
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Some diving birds are found in the Northern
Hemisphere
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Their wings can still be used for flight, so they
CANNOT dive as well as penguins can
Diving Birds – Penguins
Their wedge-shaped wings work as
flippers
 Webbed feet can be used as paddles
 Have a thick coat of feathers and a
layer of fat beneath their skin that
allows them to live in freezing
temperatures
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A rich diet of krill and fish help penguins
maintain the fat layer
Water Birds
Swan, Geese, and Ducks are
water birds, or birds found in
or near the water
 Water birds have webbed feet
for paddling
 Have long, flattened beaks
with rounded tips
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Beaks are ideal for a variety of
food such as small insects, fish,
and grass
Seabirds
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Seabirds are an unrelated group of
birds that also live near open waters,
but they are found around oceans
 They have webbed feet like water birds
 However, their beaks are longer
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Beaks are made for catching their typical
meal of fish or squid
Wading Birds
Herons, storks, flamingos, and egrets
are wading birds
 Wading birds feed in shallow waters that
are rich with fish and invertebrates
 Wading birds have long, slender
legs to feed in a range of depths
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Have long toes to keep them from
sinking into the mud
Wading Birds
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Many wading birds have spear-shaped
beaks for fishing
Fishing waders stand motionless as they wait
for fish
 When they see a fish they quickly snatch it in
their beak or may even spear it
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Waders that feed on invertebrates in the
mud may have beaks that are built for
stabbing into the mud to find prey