Transcript 6 Characteristics of Birds - NGHS

6 Characteristics of Birds
Endothermic (warm blooded)
Vertebrates (Hollow Bones!)
4 Chamber Heart
All Have Feathers
All Lay Eggs
Have Scales on Feet and Legs
Class Aves – Birds
• 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 have visited both the North & South
poles.
– The bee hummingbird of Cuba weighs 1.8 g
and is one of the smallest vertebrate
endotherms.
How do birds fly?
• The top has less “air pressure” and this
produces an UPWARD force
• (This is called lift!)
Specializations for
Flight
• Huge Flight Muscles
– Rigid Skeleton
• Fused Bones
• Uncinate Processes
• Wishbone
– Efficient Respiration
– High Body Temp
– Sophisticated
Nervous System
• Weight Reduction
– Hollow bones
– No teeth or heavy
jaws
– Only one ovary
– No urinary bladder
– Hot air sacs
Bird Skeleton
Form & Function – Skeleton
• All birds that can fly
have a large, thin
keel on their
sternum that
provides area for the
large flight muscles
to attach.
Bird Skeleton
Air Sacs
• A bird’s most obvious adaptations for flight are its
wings and feathers.
• Feathers are the feature that set birds apart from
other vertebrates.
Form & Function – Feathers
• Feathers are lightweight,
yet tough, consisting of:
– A hollow quill emerges
from the skin.
– This becomes the shaft
which bears numerous
barbs that form a flat,
webbed surface, the
vane.
• Each barb contains many
barbules.
Form & Function – Feathers
• Contour feathers are vaned
feathers that cover and
streamline a bird’s body.
– Called flight feathers if they
extend beyond the body.
• Down feathers are soft and
have no hooks on barbules.
• Filoplume feathers are hairlike – function unknown.
• Powder-down feathers
disintegrate as they grow,
releasing powder that aids in
waterproofing.
Form & Function – Feathers
• As a feather nears
the end of its growth,
keratin is deposited
to make some of the
structures hard.
• The protective sheath
surrounding the new
feather splits open,
and the feather
unfurls.
Form & Function – Feathers
• When fully grown, feathers are dead –
like mammalian hair.
• Birds molt to replace worn out feathers.
– Usually feathers are discarded gradually to
avoid bare spots.
– Flight feathers & tail feathers are lost in
pairs to maintain balance.
– Many water birds lose all their primary
feathers at once and are grounded during
the molt.
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.
Mammal Respiratory system is not as
efficient as bird system
Bird lung
Uses air sacs to make air
flow one-way through lung
•Fresh air
•Countercurrent exchange
Mammal lung
Dead end system so
•Air is stale
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.
Efficient Respiratory System
Air moves from outside
bird into posterior air sacs
by trachea
Air moves from posterior
air sacs to lungs
Air moves from lungs to
anterior air sacs
Air moves from anterior
air sacs out body by
trachea
Food & Feeding
• The beaks of birds are strongly adapted to
specialized food habits.
Digestion
• At the end of the esophagus
of many birds is the crop.
– Used for storage.
• The stomach has two
compartments:
– The first secretes gastric
juices.
– The second, the gizzard, is
lined with keratinized plates
that serve as millstones for
grinding food.
• Birds swallow small stones to
help this process.
• Owls can’t digest the bones & fur or
feathers of their prey.
– These materials are bundled together and
ejected through the mouth.
– Owl pellets can be used to determine what
the owls in a particular area have been
eating.
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.
Circulatory System
• Birds have a four-chambered heart.
– Separate systemic and respiratory
circulations.
• Fast heartbeat – faster in smaller
birds.
• Red blood cells are nucleated and
biconvex.
– Mammals are enucleated and
biconcave.
Nervous System
• Birds have well
developed cerebral
hemispheres,
cerebellum
(important for
coordinating
movement &
balance), and optic
lobes.
Senses
• Birds usually have poor sense of smell &
taste.
– Some, carnivores, waterfowl, flightless birds
have well developed sense of smell & taste.
• Birds have the keenest eyesight in the
animal kingdom and also very good
hearing.
– A hawk can clearly see a crouching rabbit a
mile away!
Reproductive System
• Male bird sperm is produced
in two testes that lie beneath
the kidneys
• Sperm passes through small
tubes called Vasa defrentia
into the males 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
• Reproductive System Cont.
• Fertilized eggs move down the oviduct, where they
receive protective covering and a shell
• Unfertilized egg consists of a nucleus, cytoplasm,
and a yoke
• 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
Male Reproductive System
• The system is very unique
and different from that of
humans.
• Sperm formation occurs
more rapidly in birds as
compared to mammals.
• It takes from one to four
days for the sperm to
travel from the testes to
the end of the ductus.
Sperm undergo
maturation in the male
reproductive tract.
Female Reproduction System
• This system is unique to birds,
unlike any other animal.
• Just like many other female
animals, the avian female
begins life with two ovaries
and oviducts.
• At hatching, the left ovary
contains all of the egg cells it
will ever have. These cells will
continue to develop once the
hen reaches an age when she
is able to reproduce.
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.
• The 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.
Characteristics of Birds
• All birds also have hindlimbs
adapted for walking,
swimming, or perching.
– Foot structure in bird feet
shows considerable variation.
• All have keratinized beaks.
• All lay shelled amniotic
eggs.
Birds who do NOT fly!
• Penguins
• Ostriches
• Emus
Living Birds
• Flightlessness has
evolved in many groups
of birds.
– Penguins (use wings to
swim through water).
– Many fossil forms
including flightless owls,
pigeons, parrots, cranes,
ducks, & auks.
– Usually occurs on islands
with few predators.
Smallest / Largest
Hummingbird
Ostrich
The Origin of Birds
• Birds probably
descended from
theropods – a
group of small,
carnivorous
dinosaurs.
• By 147 million
years ago,
feathered
theropods had
evolved into birds.
Evolution of Flight
• As the reptile line leading to birds became
endothermic, the ability to conserve heat
(insulation) was selected for.
– Longer scales = better insulation, up to a point
– At this longer length, besides providing better
insulation, the scales provided lift for gliding.
• Now both insulation and lift were selected
for, and feathers, wings, etc. evolved.
Retained Dinosauran
Features
• Egg-laying
• Feathers as
modified scales
(new evidence
indicates
Velociraptors may
have had feathers)
• Air Sacs
The Origin of Birds
• Archaeopteryx
– The oldest bird known.
– Skull similar to modern birds but with thecodont
teeth.
– Wings with feathers were present.
The Origin of Birds
• Much of the skeleton was
that of a theropod
dinosaur.
–
–
–
–
Long bony tail
Clawed fingers
Abdominal ribs
S-shaped, mobile neck
• This fossil demonstrated
the connection between
theropods & birds.
The Origin
of Birds
• Archaeopteryx
arose from the
theropod lineage.
• Closely related to
Dromaeosaurs.
– More shared
derived
characters.
– Many had
feathers used
for insulation
and/or social
display.