Chapter 19 and 20 Notes,
Birds and Mammals
Characteristics of Class Aves
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Forelimbs designed for flight in most birds.
Epidermis is covered in feathers, except the
hind legs which are covered in scales.
No sweat or oil glands, but they do have a
preen gland at the base of their tail, that they
use to waterproof and protect their feathers.
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Bony skeleton that is filled with air cavities.
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Skull with keratin beak, but no teeth.
Preen (Uropygial) Gland
Characteristics of Class Aves
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4-chambered heart, with separate pulmonary and
systemic circulations.
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Endothermic, warm blooded.
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Respiration by air sacs.
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No urinary bladder, semisolid urine as waste.
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Sexes separate, internal fertilization.
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Amniotic egg, with hard calcareous shell.
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Eggs are incubated externally.
Air Sac Respiratory System
Feathers
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Almost everything about birds, with the exception of
the flightless birds, is centered around two principles;
more power, less weight.
Feathers being made of keratin, are lightweight, yet
amazingly tough and resilient.
Most feathers are contour feathers, which are the
feathers used for flight.
Contour feathers emerge from the skin at the quill
(calamus), and turn into the shaft (rachis), which
bears numerous barbs.
Feathers
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The barbs branch out diagonally from the shaft
(rachis) to form the vane.
There are several hundred barbs in a vane.
Each barb has separate parallel filaments that branch
off from the barbs called barbules.
The barbules hook on to each other to keep the vane
of the feather aligned.
Each barb can have up to 600 barbules on each side
of the barb. A single feather can have over 1 million
barbules.
Contour Feather
Different Types of Feathers
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The three different
basic types of
feathers are
Contour feathers
(Flight feathers)
Down feathers
(Insulation feathers)
Filoplume feathers
(Sensory feathers)
Feathers
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If the barbules become unattached, the birds
preen their feathers to reattach them.
Feathers, like hair, are dead once fully grown.
Shedding or molting of feathers replaces old,
worn out feathers.
Molting usually occurs once a year, usually in late
summer after nesting season.
Flight and tail feathers are lost gradually and in
pairs, so the molting doesn't impair flight.
Peregrine Falcon Preening its Feathers
Bird Skeletal Structure
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Bird's bones are pneumatic, which means they have
air-filled cavities.
The pneumatic bones make birds light, but they also
play a role in the respiratory system of birds.
This bone structure makes them incredibly light.
The frigate bird has a 7-foot wingspan, but the
skeleton only weighs a mere ¼ pound.
In order to increase the strength of the hollow bones,
the inside of the bones have cross members or struts
like on an airplane.
Frigate Bird
Birds Pneumatic Bones
Bird Skeletal Structure
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The orbits (eye sockets) of birds are unusually large to
accommodate their excellent vision.
Modern birds lack teeth. Some birds in the fossil
record had teeth, like the famous archeopteryx.
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Teeth are very heavy.
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Instead birds utilize a muscular gizzard.
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The rib cage and sternum is rigid, not allowing
expansion of the chest cavity for respiration.
The rib cage and sternum must support the powerful
wing muscles on the breast.
Bird skulls
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Archeopteryx Skull
Raven Skull
Bird Skeletal Structure
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The sternum is keeled, meaning it has a very
large surface area for muscle attachment.
The clavicles are fused to form an elastic
structure called the furcula, which stores elastic
energy when the wing beats in flight.
The furcula is the Y-shaped bone that we call
the wishbone at Thanksgiving.
The vertebrae and pelvis are also fused to
absorb the shock of landing.
Elastic Wishbone (The Furcula)
Bird Skeleton
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Note the unusually
large keeled sternum
that attaches to the
breast muscles
Note the fused pelvis
with the vertebrae
called the synsacrum,
which absorbs the
shock of landing.
Bird Muscular System
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If you have ever eaten a bird you know that
most of the muscle in the body is on the breast.
The largest muscle which pushes the wing
down during flight is the pectoralis muscle.
The pectoralis muscle also has an antagonistic
muscle that brings the wing back up, but
surprisingly it is not found on the back where
one might expect. If it was, it would impair flight
by making the bird too top heavy.
Flight Muscles
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Instead, there is
another muscle
found underneath
the pectoralis
muscle called the
supracoracoideus
muscle and it has
an ingenious rope
and pulley system.
Leg Muscles and the Perching
Mechanism
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Muscles of the lower leg are greatly reduced because
large leg muscles would affect a bird's center of
gravity and it would make the legs vulnerable to cold.
Birds have strong tendons that automatically clamp
down when a bird is perched, allowing them to sleep
while they are perched.
Also, the talons on raptors, like hawks, eagles, and
falcons are assisted by these tendons.
The force of the strike causes the tendons to clamp
down hard on its prey.
The Perching Mechanism
Birds Digestive System
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Birds lack teeth because teeth are too heavy.
Instead, birds use a muscular gizzard that they fill
with small stones and pebbles to grind food.
Storage of food takes place in the crop.
A chamber called the proventriculus is the actual
stomach and it secretes gastric juice which
chemically breaks down the food.
Birds of prey like owls, form pellets of indigestible
material (bones and fur) in the proventriculus, then
they regurgitate them.
Birds Digestive System
Birds Respiratory System
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The respiratory system of birds is arguably the most
efficient in the animal kingdom.
It is no surprise considering how hard they have to
work in order to achieve flight.
For example, bar-headed geese migrate over the
great Himalayan Mountains.
They have even been observed flying over Mount
Everest at 29,000 ft elevation.
Not only that, but they do it all in one day without
having to acclimate to avoid hypoxia.
Birds Respiratory System
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The secret to their success is a one way
(unidirectional) flow of oxygen, created by 9 air sacs
distributed throughout the body, and tubes in the
lungs called parabronchi.
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Air sacs connect to the bones via tubes.
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There are both anterior and posterior air sacs.
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It takes two full breaths for air to circulate the body.
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On the first inhalation, the oxygen rich air moves
back to the posterior air sacs.
Birds Respiratory System
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On the first exhalation, the air from the posterior air
sacs moves into the lungs to deliver oxygen to the
vascularized parabronchi.
On the second inhalation, the air from the parabronchi
moves into the anterior air sacs.
On the second exhalation, the air from the anterior air
sacs is removed from the body.
The result is a constant flow of fresh air across the
blood vessels surrounding the parabronchi.
Birds Respiratory System
Birds Respiratory System
Wing Shapes
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There are four basic wing shapes found among birds
to assist them in different ways.
Elliptical (low aspect ratio) designed for low speeds
while maintaining high lift and maneuverability.
High-speed (tapering or sweep back wings) for high
speeds and reduced turbulence.
Soaring (high aspect ratio) for high lift and speed but
low maneuverability.
High-lift for carrying heavy loads at low speeds with
moderate maneuverability.
Wing Shapes
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Two wing designs that reduce turbulence or stalling of an
airfoil is wing slots (or alula) or a sweep back tapering
wing which reduces wing tip vortexes.
Wing Slots and Wing Tip Vortexes
Wing Slots and Wing Tip Vortexes
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Geese take advantage of the wing tip vortexes by
flying in a V and catching the updrafts.
Bird Migration
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Birds are the supreme migrators of the animal
kingdom. The Arctic tern migrates to the Arctic Circle
during the summer to breed. Then they migrate all
the way to Antarctica during the winter. A total round
trip distance of about 22,000-30,000 miles.
The stimulus for migration is an increase of daylight
in the early spring.
This also stimulates an increase in gonad
development, increase of fat storage, courtship and
mating behavior and care of their young.
Arctic Tern Migration Route
Migration Navigation
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Understanding exactly how birds navigate is not
entirely understood by scientists.
Experiments have shown that some birds navigate by
sight and recognizing landmarks.
Experiments with homing pigeons have shown that
the earth's magnetic field may help some birds to
navigate. Small particles of magnetite have been
detected in their neck muscles.
Other experiments have shown some birds use the
position of the sun and stars to navigate.
Mating Strategies
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There are two main types of mating strategies in
animals; monogamy, in which mating occurs with
only one partner, and polygamy, in which mating
occurs with multiple partners.
There are many variations of the two types.
Monogamy is rare in most animals, but very common
with birds; approximately 90%.
One reason why monogamy may be more common
with birds than other animals like mammals is that
birds lack milk, so parental roles are more equal.
Mating Strategies
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The most common form of polygamy in birds is
called polygyny.
Polygyny is when one male has many female
partners. This is a common practice with some
members of the grouse family.
Male sage grouse defend their breeding territories
(called leks) from other rival males.
The females choose the dominant male because
he has the best genes.
Sage Grouse Lek
Nesting and Care of the Young
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Most birds build some type of nest in order to
prepare a place to raise their young.
There are two ways the young are born.
Precocial young such as quail, fowl, ducks etc.
are born covered with down and can run or swim
as soon as their plumage is dry.
Atricial young are born naked and helpless at
birth and remain in the nest for a week or more.
Most birds (the passeriformes) are altricial.
Precocial Ducklings
Altricial Chicks
Class Mammalia
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Body covered in hair, reduced in some.
Skin glands including, sweat, scent,
sebaceous, and mammary glands.
Turbinate bones in the nasal cavity that
conserve water for endotherms and also
give mammals an acute sense of smell.
Teeth are diphyodont (deciduous or milk
teeth), and also heterodont (varying in
both structure and function).
Turbinate Bones in Mammals
Nasal Passages in a Reptile
Class Mammalia
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Fleshy external ears called pinnae.
4-chambered heart and red blood cells are
biconcave and nonnucleated.
Secondary palate, which separates the air
passages from the food.
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A muscular diaphragm for breathing.
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A highly developed, cerebral cortex.
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Internal fertilization, with development via a
placenta in most, young nourished from milk.
Hair
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All mammals have hair. Humans have very
little, and whales usually only have a few
sensory hair bristles on their snout.
Hair is made from keratin, the same substance
that makes up nails, claws, hooves, horns,
feathers on birds, and scales on reptiles.
Mammals have two kinds of hair that make up
their pelage (coat); dense, soft underhair for
insulation, and coarse, long guard hairs used
for protection and camouflage.
Hair
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Most animals undergo two annual molts. Many
arctic animals like the weasels and snowshoe
hare, have a brown to gray summer coat that is
thin, and a white winter coat that is thick.
Many mammals have unusual color patterns
like the zebra's coat which confuses attacking
predators, to the white spots on a fawn which
imitates sunlight through the forest canopy.
Green is a rare color for mammals, possibly in
response to nocturnal behavior.
Camouflaged Fawn
Hair
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Many hairs are also used for defense and
sensory purposes, like the quills on a
porcupine, and the vibrassae (whiskers)
found on a variety of mammals. An
adaptation for nocturnal behavior.
Horns and Antlers
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Horns are hard keratinized structures that grow
from a bone on the skull and are not shed
annually. They are found on members of the
Bovidae family (sheep and cattle), and they are
usually found on both sexes.
Antlers are hard structures made of solid bone
when mature, and are found in the Cervidae
family (deer family). Antlers are shed annually,
usually in the winter, and they regrow in the
spring under a vascularized velvet.
Horns and Antlers
Integumentary (Skin) Glands
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Mammals have a complex integumentary
system and skin glands.
The four different skin glands are sweat,
sebaceous, scent, and mammary glands.
Sweat glands are for evaporative cooling.
Scent glands produce pheromones for
attracting mates, for marking territories or
for defense (like in the case of a skunk).
Integumentary Glands
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Sebaceous glands are closely associated with
hair follicles and secrete an oily substance called
sebum onto the hair and skin. Sebum protects
and waterproofs the skin and hair of mammals.
In most mammals, milk is secreted from
mammary glands through nipples or teats.
Monotreme mammals lack nipples and secrete
milk into a depression on the mother's belly.
Teeth
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The dentition or teeth in mammals are complex.
Mammal's teeth vary in shape and form,
relative to their function. These types of teeth
are referred to as heterodont teeth.
There are four basic types of heterodont teeth;
incisors for snipping, canines for piercing, and
premolars and molars used for shearing,
slicing, crushing, or grinding.
Heterodont Teeth
Deciduous (Milk) Teeth
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Mammals grow two sets of teeth; a temporary
set, called deciduous teeth, or milk (baby)
teeth, and a permanent (adult) set of teeth.
Only incisors, canines, and premolars are
deciduous, molars are never replaced.
Adaptations for Feeding
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There are four different ways mammals obtain
their food. Their dentition varies with diet.
Mammals can be either Insectivores,
Herbivores, Carnivores, or Omnivores.
Insectivores like shrews, moles, anteaters,
and bats feed on small invertebrates like
worms, grubs, and insects. Insectivores have
teeth with pointed cusps, which puncture the
exoskeletons of their prey.
Insectivorous Teeth of a Shrew
Adaptations for Feeding
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Herbivores can be divided into two groups.
The first group is the browsers and grazers like
the ungulates (hoofed animals like the horses,
deer, antelope, cattle, sheep, and goats).
The second group is the gnawers like the
rodents and rabbits.
Rodents have chisel-like incisors which
continue growing for life and must be worn
away to keep pace with their continual growth.
Herbivore Skulls
Adaptations for Feeding
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Herbivores also have the added challenge of
breaking down cellulose, the structural part of
plants. Vertebrates lack cellulases (digestive
enzymes for breaking down cellulose).
Herbivores harbor anaerobic bacteria and
protozoans in their digestive systems that can
produce cellulases.
In some herbivores, such as horses, rabbits,
elephants, some primates, and rodents, the
bacteria are found in the cecum.
Adaptations for Feeding
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In some non-ruminant herbivores like the
lagomorphs (rabbits and hares), much of the
nutrition is lost because fermentation of the
cellulose occurs after the small intestine.
In order to compensate, rabbits reingest their
fecal pellets in order to extract as much of the
nutrition from their food as possible. This type of
feeding strategy is referred to as coprophagy.
Ruminants (cattle, goats, sheep, deer etc.) have
a four-chambered stomach.
Adaptations for Feeding
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The first of the four stomach chambers of a
ruminant is called the rumen. The food is broken
down by bacteria in the rumen and is formed into
small balls of cud. When the animal lays down to
rest, it regurgitates the cud into its mouth to chew
it into smaller pieces. Then the cud is reingested
and it passes back through the rumen.
Then it passes into two other chambers referred
to as the reticulum and omasum, where water
and some of the nutrients are absorbed.
Adaptations for Feeding
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The remainder of the food products are passed
into the last chamber, called the abomasum and
small intestine, where enzymes are secreted and
normal digestion occurs.
Because there is very little nutrition obtained from
vegetation, herbivores have to consume large
quantities to obtain their nutrition.
Large African elephants have to consume as
much as 300-400 lbs. of vegetation a day!
Adaptations for Feeding
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Carnivores, like canines, felines, and members
of the weasel family, are well equipped with
large canine teeth and carnassial cheek teeth
that are designed for tearing flesh and meat.
Their digestive tracts are short compared to the
herbivores, and their cecums very small since
their food is easily digestible.
Omnivores (bears, pigs, raccoons, rodents,
primates) have digestive tracts and teeth that
allow them to eat both plants and animals.
Digestive Tracts of Mammals
Dentition (Teeth) of Mammals
Reproduction in Mammals
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Most male mammals are fertile year round,
however mating is restricted to times of fertility
in females. Fertility in female mammals runs in
periodic cycles referred to as estrus cycles.
Only when a female mammal goes into heat or
estrus, may she successfully breed.
There are three different methods of breeding
found in mammals. One group of mammals,
the monotremes, are oviparous (lay eggs).
Monotremata (Duck-Billed Platypus
and the Echidna or Spiny Anteater)
Reproduction in Mammals
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Marsupial mammals are viviparous, but the
young are born underdeveloped, live in the
mother's pouch for a long period of time known
as the lactation period, and they drink milk in
their mother's pouch.
Placental mammals are viviparous, but the
young remain attached to the placenta for a long
period of time known as the gestation period.
After the young are born, the lactation period is
shorter than that in the marsupials.
Marsupial Mammals