Class Aves
{ Birds
Class Aves (Birds)
Ornithologist –
Zoologists that
study birds

Characteristics of Birds
Vertebrate
 Feathers
 Wings (but not all fly)
 Scale-covered legs
 Homoeothermic (Keeps their body
temperature at one temperature)
 Endothermic (Warm blooded)

Designed For Flight
The following characteristics equip birds
for flying:
 Compact, lightweight, and very strong
skeleton
Designed For Flight

A nearly rigid backbone that gives a solid
support for the strenuous muscle activity
required for flying
Designed For Flight

Hollow spaces in the
skeleton that provide
room for air sacs, which
contribute to the
efficiency of the
respiratory system and
make the bird lighter.
Designed For Flight

Bipedal (“twofooted”)
anatomy, which
leaves the wings
free for flying.
Designed For Flight

A prominent ridge, or
keel, on the breastbone
to allow for the
attachment of flight
muscles by strong
tendons.
Designed For Flight

Three bones in the shoulder to
support each wing.
Designed For Flight

Lightweight beaks
and skulls.
Designed For Flight

An efficient circulatory system,
including a four-chambered heart.
Designed For Flight

Powerful muscles to
power the wings
during flight.
Groups of Birds
Perching Birds
Three toes pointing forward
and one toe pointing
backward.
 Leg has a special design that
allows the bird to stay on their
perch even if they are sleeping.

Thrushes
Robins
Bluebird
Goldfinch
House Sparrow
Humming Bird
Woodpecker
Birds of Prey
Especially acute eyesight
 Sharp, Powerful talons (grasping and
killing their prey)
 Hooked Beak

Vultures
California Condor
Sea Eagle
Bald Eagle
Golden Eagle
Hawks
Osprey
Falcons
Owls
Swimming and Wading Birds –
Many have water repellent feathers
 Webbed or Lobed feet for swimming
 Some birds have very long legs
designed for wading

Ducks
Geese
Storks
Herons
Flamingos
Cranes
Egrets
Game Birds
Have been hunted for food and sport
 Large flight muscles (Breast meat)
allow them to burst into flight

Quail
Pheasant
Partridge
Grouse
Doves
Turkey
Tropical Birds
Live in the world’s tropical forests
 Brightly colored
 Many have large unusual beaks

Parakeets
Toucans
Macaw
Flightless Birds
Have wings or wing-like structures
 Usually equipped with powerful
legs for running

Ostrich
Emu
Kiwi
Penguins
Extinct Birds
Some became extinct because of the
pressures put on their habitat
 Some have been extinct for thousands of
years

Dodo
Moa
Great Auk
Passenger Pigeon
Archaeopteryx
Diatryma
Family Life of Birds
{
Migration
Generally migrate in flocks
 Can migrate short distances or
thousands of miles

North American Blue
Grouse

Migrates about 300
miles, one of the
shortest
Arctic Tern

Migrates 11,000
miles each time
from Antarctica to
the Arctic
Migration

Can migrate slowly or in one
continuous flight
Redwing Blackbird

Migrate slowly
Golden Plover

Flies nonstop for
several days on
flight from Canada
to South America
Migration
Many mysteries still abound in
understanding migration
 This is what we do know:

Migrating birds follow the
same route each year
They use a sense of direction
and recognize landmarks

Migration
Stars and constellations are used as
landmarks
 Some birds use the Earth’s magnetic field
 The amount of daylight can trigger
migration
 Urge to migrate can be linked to breeding
 Migration generally occurs in the spring
and fall
 Migration is generally north and south

Courtship
Males establish territory
 Males have unique colors, plumage,
and/or songs that help to attract a
mate
 Some birds mate for life, some for a
season
 Some have long engagements

Frigate Bird
Greater Prairie Chicken
Mating and Fertilization
Mating occurs after courtship
 Male sperm passes from the testes to
the cloaca of the female
 In the most species, the left ovary and
oviduct is the only functioning pair
 Egg cells are released by the ovary and
go to the oviduct

Mating and Fertilization
Albumen is added to the egg cell
 Sperm migrate up the oviduct and
fertilize the egg as it descends to the
cloaca
 This can happen in minutes or months
 Shell is added at the end of the oviduct
 The egg is then laid

The Egg
Yolk is the egg cell
 Germinal spot is the embryo on the
yolk
 Egg white is albumen – protects yolk
and is an additional food source
 Egg shell is made of calcium and has
tiny pores for air
 Chalaza keeps yolk upright when eggs
are turned so the embryo is always
upright

Nesting
Eggs are laid in already prepared nests
 Some nests are simple and some are
complex
 Nest-building is an instinct – parents
do not teach young how to build nests
 The purpose of the nest is to protect
the egg

Robin nest

Made of twigs and
grass
Barn Swallow nest

Made of mud
Killdeer nest

Made of stones
Oriole nest

Nest hangs from
branches
Osprey nest

High, built near
water
Incubation
During incubation, eggs must be kept
warm, usually by a parent laying on
them
 Incubation must happen continually
or the egg will die
 Feathers are not good heat
conductors, so birds will lose feathers
and form a brood patch so their skin
is on the eggs
 In most species, male and female take
turns incubating the eggs

Incubation
Many birds don’t start incubating
until a clutch has been formed
st
 1 eggs are dormant until incubation
starts
 Eggs are turned to eliminate cold
spots

Emperor Penguin

Emperor penguin
keeps the egg at 93
degrees for 8-9
weeks with air
temperatures at 77
below 0
Hatching
Can take from 11-87 days depending
on the species
 Altricial – naked and helpless when
born
 Most song birds are altricial
 Precocial – covered with down, able
to run or swim almost immediately
 Most water and ground birds are
precocial

Feeding
Precocial birds are taught to eat right
away
 Altricial birds have food brought to
them by parents
 Some parents will store food and
regurgitate it in the nest for the young
or the young will reach into the parent’s
gullet
 Doves and pigeons produce crop milk

Cardinal feeding young
Golden Eagle feeding
young
Flamingo
about to
receive crop
milk
Avian Anatomy and
Physiology
{
Feathers

Purpose
Lightweight body covering
 Good insulators
 Provide a smooth, tapered,
streamlined body shape
 Increase the surface area of the
wings

Feathers
Types

Contour

Strong
 Found on bird’s body, wings,
and tail
 Point toward the tail
 Aid in streamlining

Feathers
Flight


Special contour feathers on the
wing
Down

Soft fluffy feathers
 Provide excellent insulation
 Don’t add weight

Feathers
Parts of a Feather
 Rachis – stiff quill
 Barbs – vane of the
feather (several
hundreds per vane)
 Barbules – connect
barbs together
The Incredible Feather
By design, a feather can change shape
during flight in response to different
pressures in the air
 Most of the feathers are designed to give
lift

The Incredible Feather
Some feathers are designed as ailerons
and flaps to control direction and give
extra lift.
 The tail feathers serve as a rudder and
elevator to control flight direction.

The Incredible Feather

There are nerve endings near the end of
each feather that turn the feathers into
sensory receptors
Flight Patterns
Powered Flight – Flap with a
downward stroke of the wings to
produce lift
 Gliding – Use of the air movement to
“fall” slowly and gracefully

Flight Patterns
Soaring – Use of the thermal upcurrents to rise in a circular pattern.
Birds can dive and start climbing again
 Special Flight Patterns – Complicated
motion of the wings produce a vertical,
reverse or hovering flight.
(Hummingbird and Skylark)

Skeletal System
Strong and
lightweight
 Filled with air
 Strengthened by
internal cross
bracing
 Only 5% of a bird’s
weight compared
to 14% of human

Skeletal System
Large sternum,
extends out from
the rib cage
 Called the keel
 Mounting point for
powerful flight
muscles

Skeletal System
Light weight skull
 Toothless
 Lightweight bills
made of keratin
 Thin cranial bones
 Short humerus –
strength for
attachment of
flying muscles

Muscular System
Pectoralis major – pulls the wing down
in the “power stroke”
 Pectoralis minor – raises the wing after
each stroke; operates like a rope and
pulley
 Reduces need for strong back muscles

Muscular System
Nervous System
3 parts of the brain
 Cerebrum
 Two hemispheres
 Controls
voluntary
behavior
 Allows for dayto-day decisions

Nervous System
Cerebellum
 Muscle coordination
 Processes sensory
messages
 Brain stem
 Controls automatic
functions
 Controls optic lobe
 Optic lobe much larger
in birds than mammals

Senses
Poor sense of smell and taste
 Excellent hearing
 Does not have an outer ear (would be
less streamlined)

Senses
Tube leads to eardrum
 Have a single bone and a cochlea that
transmit the sound
 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

Senses - Eyesight
Bird’s eyes are almost completely
immovable
 Turn their head to look around
 Less spherical than a human eye
 Have a nictitating membrane
 Allows birds to moisten the cornea
without closing their eyes (bad idea for
flight!)

Bird’s eye and Human’s
eye
Eyesight

Reasons for good vision
Larger eye than human
 Many more rod (light) and cone (color)
cells
 More than one fovea (depression in the
retina where the sharpest focus is)
 Can see the color spectrum PLUS much of
the UV range of the spectrum

Digestive System
Relative small size and great activity
requires a great deal of fuel
 Birds absorb a very high percentage of
the food they eat.
 Birds are able to eat and digest their
food quickly

Digestive System

Different birds
have different bills
designed for what
they eat
Special Parts of the Digestive
System

Crop – Many birds
have a special sac in
their esophagus that
serves as a storage
chamber. Will release
food at a proper rate
to the rest of the
system
Special Parts of the Digestive
System

Gizzard – A chamber
of the digestive
system found after the
stomach that is
muscular, has horny
plates, and sometimes
contains grit to help
grind the food up.
Special Parts of the Digestive
System

Cloaca – Area of the digestive system
where the waste is expelled. Also
where the sperm is received for
reproduction, where the eggs are
released and where the wastes from the
kidneys are released.
Excretory System
Birds can completely digest food in 45
minutes and get rid of the waste
 Birds produce uric acid instead of
urea. This does not have to be
dissolved in water and keeps water in
the bird.

Excretory System
Birds release their uric acid through
the cloaca
 Uric acid does not contain much water
like urea, so birds can conserve water

Excretory System
Some birds have a salt gland, which
takes salt out of their body and puts it
into a salty solution that runs through
a duct in the nostril.
 The salt gland allows marine birds to
get the water they need by drinking
seawater

Circulatory System
Have a four-chambered heart
 Have a high metabolism to keep the
body at a constant temperature, so
they have a rapid heartbeat

Circulatory System
Respiratory System
The respiratory system is completely
different from every other living
vertebrate.
 Breathes “through” their lungs instead
of “into” their lungs
 Lungs do not expand or contract

Respiratory System
With this different way of breathing, birds
are able to take more oxygen out of the air
 Respiratory system allows birds to fly at
high altitudes and have enough oxygen
 The air sacs of birds are used to cool the
body during flight.

Respiratory System
Specially Designed Respiratory
System
The bird’s “voice box” (syrinx) has a
membrane that vibrates when air passes
over it.
 Some birds have two membranes that
allows them to produce two different
notes at once
