CHAPTER
Birds
27-1
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
27-2
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Diversity
Profile




27-3
Over 9,700 species have been
described worldwide
Birds live in all biomes, from mountains
to prairies, on all oceans, and from the
North to the South Pole
Some live in dark caves, and some dive
to 45 meters depth
The “bee” hummingbird is one of the
smallest vertebrate endotherms
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Diversity

The feather is the unique and essential
feature or hallmark of birds



27-4
Some feathers were also present in some
dinosaurs
These feathers were not capable of supporting
flight
Obviously served in other capacities such as
thermoregulation or mating behavior
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Diversity

Uniformity in Structure




27-5
Forelimbs are modified as wings, although not all
are capable of flight
Hindlimbs are adapted for walking, swimming or
perching
All birds have horny, keratinized beaks
All birds lay eggs
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Diversity

27-6
Driving force for this uniformity appears to be
adaptations necessary for flight
 Wings
 Present for support and propulsion
 Respiratory system
 Must meet high oxygen demands and cool
the body
 Bones
 Must provide a light but rigid airframe
 Digestion and circulation
 Must meet high-energy demands of flight
 Nervous system
 Must have superb sensory systems for highvelocity flight
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Origin and Relationships
History

Discovery of the fossil of Archaeopteryx
lithographica in 1861 linked birds and
dinosaurs



27-7
Skull resembled modern birds but had teeth rather
than a beak
Skeleton was reptilian with clawed fingers,
abdominal ribs, and a long bony tail
Feathers were unmistakably imprinted along wings
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Archaeopteryx - 147 million year old ancestor of bids
27-8
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Origin and Relationships

Zoologists had long recognized that
birds and reptiles shared many
similarities
Single middle ear bone, the stapes
 Lower jaw composed of five or six bones



Excrete nitrogenous wastes as uric acid


27-9
Mammals have one mandibular bone
Mammals excrete urea
Similar yolked eggs
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
27-10
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
27-11
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Origin and Relationships
Relationships

Modern birds include:

Paleognathae (Ratite)



Neognathae



with a keeled sternum (keel is an extension of sternum for high
muscle attachment)
All other birds
Original theories were based on ability to fly



Large flightless birds
with a flat sternum (no keel extension)
Now rejected
Flightlessness has evolved many times among bird groups
Smaller birds can revert to flightlessness on islands
that lack terrestrial predators
27-12
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cormorant: Flightless
Neognathae Bird (keeled sternum)
Lives in Galapagos
Excellent Swimmer
27-13
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Origin and Relationships


Larger flightless birds such as the ostrich
and emu can outrun predators
Flightless birds are free from weight
restrictions of flight and some evolved to
very large sizes
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
27-14
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural and Functional Adaptations for Flight
Feathers

Structure





Feather is a special bird adaptation that
contributes to more power or less weight
Hollow quill emerges from skin follicle and
continues as a shaft or rachis
Rachis bears numerous barbs
Up to several hundred barbs are arranged to form
a flat, webbed surface, the vane
Each barb resembles a miniature feather

27-15
Numerous parallel filaments or barbules spread laterally
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
A - E: Development
Of Contour Feather
Protective Sheath splits open
when growth is complete.
G: Filoplumes
Hairlike, connected to
nervous system
H: Down Feather
(no hooks)
Function -Conserve Heat
27-16
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural and Functional Adaptations for Flight

Up to 600 barbules in each side of a barb


Barbules from two neighboring barbs overlap


27-17
May be over one million in the whole feather
“Zip” together with tiny hooks
When separated, they are “zipped” back together
by preening
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural and Functional Adaptations for Flight

Types of Feathers

Contour feathers
Provide the form of the bird
 Flight feathers are contour feathers that extend
beyond body


Down feathers
Under contour feathers
 Barbules lack hooks and function as insulation


Filoplume feathers

27-18
Hairlike, degenerate feathers with a weak shaft
and tuft of short barbs
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural and Functional Adaptations for Flight

Origin and Development






27-19
Bird feather is homologous to reptile scale
Feather develops from an epidermal elevation
over a nourishing dermal core
Rather than flattening, feather bud rolls into a
cylinder
During growth, pigments are added to the
epidermal cells
Near the end of its growth, soft rachis and barbs
transform into hard structures of keratin
When the protective sheath splits apart, the
feather protrudes and barbs unfold
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural and Functional Adaptations for Flight

Molting

Fully-grown feather is a dead structure




Except in penguins, molting is a gradual process
that avoids leaving bare spots
Flight and tail feathers are lost in pairs, one on
each side, to maintain balance
In some species, replacement is continuous


27-20
Flight is unimpaired
In many water birds, primary feathers are molted
all at once


Shedding or molting is an orderly process
Birds are temporarily grounded
Most birds molt once a year, usually in late
summer after the nesting season
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Osprey feathers molt in sequence with exact pairs to
maintain balance during flight.
27-21
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural and Functional Adaptations for Flight
Skeleton

Bone Weight

Compared with the Archeopteryx




27-22
Modern birds have light, delicate bones laced with air
cavities
Termed pneumatized bones
Very strong
Total weight of a bird’s feathers may outweigh
skeleton
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
A. Skeletal Structure of Birds
B. Skeletal Structure of
Archaeopteryx
Blue: reptilian bones that are
retained, lost, or modified
Red: New structures not
present in reptiles
27-23
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Hollow Wing Bone:
(Pneumatized)
Shows Struts and
Air Spaces
Strut
27-24
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural and Functional Adaptations for Flight

Except in flightless birds

Sternum bears a large keel to anchor flight
muscles
Muscular System

Pectoralis muscles


Depress the wing in flight and attached to the keel
Supracoracoideus muscle



27-25
Raises the wing, is also attached to the keel
Lays under the pectoralis muscles
Pulls the wing up from below by way of a “ropeand-pulley” type of arrangement
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Flight Muscles:
Contraction of pectoralis
pulls wing down.
Contraction of
Supracoracoideus pulls
wing upward.
27-26
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural and Functional Adaptations for Flight



Main leg muscle mass is in thigh with
connections by long tendons to feet
and toes
Toe-locking mechanism prevents a
perching bird from falling off a branch
while asleep
As many as 1000 muscles may control
the tail feathers for steering in flight
27-27
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Tendons
automatically
tighten, closing
toes around the
perch
27-28
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural and Functional Adaptations for Flight
Food, Feeding and Digestion

Insect Eaters



Early in their evolution, birds were carnivorous
 Primarily feeding on the great variety of insects
Modern birds have specialized to hunt nearly all types of
insects in most habitats
Beaks of birds often reveal their food habits
and vary between seed-eaters, insect-eaters,
etc.


27-29
Woodpecker has a straight, hard, chisel-like beak to
expose insect burrows
Long, flexible, barbed tongue seeks out insects in wood
galleries
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Different bills
of birds
showing adaptations
to different
environments
27-30
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural and Functional Adaptations for Flight

Food Quantity


Birds are BIG feeders
Have a high metabolic rate


Hummingbirds use oxygen 12 times faster than a
pigeon and 25 times that of a chicken




Eats 100% of body weight each day
Canary about 30%
Chicken about 3.4%
Have rapid and efficient digestive systems


27-31
Small birds need even more food per body mass
A shrike can digest a mouse in 3 hours
A thrush will pass berries through the tract in just 30
minutes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Loggerhead Shrike
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Blue-Whistling Thrush
27-32
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural and Functional Adaptations for Flight

Because birds lack teeth


Salivary glands are poorly developed




Lubricate food and tongue
Few taste buds
Many have a crop that serves to store food at
lower end of esophagus
Crop of pigeons, doves, and some parrots, also
produces a lipid- and protein-rich “milk”

27-33
Foods that require grinding are cut apart in the gizzard
Regurgitate during nesting season and feed to young.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Stomach: 1st Chamber
Stomach’s 2nd chamber: Gizzard
Crop will store food and also regurgitate during nesting time for young.
1st chamber of stomach secretes enzymes and acid to help break down food.
Muscular walls of Gizzard move around contents and stones help break down food
27-34
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural and Functional Adaptations for Flight

Stomach consists of 2 chambers:

1st: Proventriculus


2nd: Gizzard



Form a pellet of indigestible material in the
proventriculus and eject it
End of the digestive system is the cloaca

27-35
Grinds food
Birds may swallow pebbles or grit to assist
grinding in gizzard
Birds of prey such as owls


Secretes gastric juice
Also receives products from genital ducts and ureters
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural and Functional Adaptations for Flight
Circulatory System


4-chambered heart is large, with strong
ventricular walls
Share with mammals:


complete separation
(oxygenated/deoxygenated)
Brachial and pectoral arteries to wings
and breast are unusually large
27-36
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural and Functional Adaptations for Flight
27-37
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural and Functional Adaptations for Flight

Heartbeat relatively fast compared to
mammals and inversely proportional to size



Turkey heart beats 93 times per minute
Chicken heart beats 250 times per minute
A small black-capped chickadee heart beats 500
times per minute
QuickTime™ and a
TIF F (Uncompressed) decompressor
are needed to see this picture.

Mobile phagocytes are efficient in repairing
wounds and destroying microbes
27-38
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural and Functional Adaptations for Flight
Respiratory System


Differs radically from lungs of reptiles and
mammals
Bird Lungs


Finest branches of the bronchi do not terminate in
alveoli but are tube-like parabronchi
Air sacs



Large portion of air bypasses lungs and flows
directly to posterior air sacs on inspiration
On expiration, oxygenated air flows through lungs



27-39
Extend into thorax, abdomen, and long bones
Continuous air flow to anterior air sacs, then exits
Takes 2 respiratory cycles for a single breath of air
to pass through system
Most efficient respiratory system of any vertebrate
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
One side of lungs
and air sacs
27-40
Showing 2 cycle process of respiratory system
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural and Functional Adaptations for Flight


An air sac system helps cool bird during
vigorous exercise when up to 27 times more
heat is produced
Air sacs extend into bones, legs and wings,
providing considerable buoyancy
27-41
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural and Functional Adaptations for Flight
Excretory System




Pair of large kidneys is composed of many
thousands of nephrons
Birds use vertebrate pattern of glomerular
filtration and selective resorption
Urine flows through ureters to the cloaca
Uric Acid

27-42
Birds also use the reptilian adaptation of
excreting nitrogenous wastes as uric acid
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural and Functional Adaptations for Flight

Marine birds excrete larger salt loads due
diet and seawater they drink



27-43
Salt glands located above each eye excrete highly
concentrated solutions
Salt solution runs out the nostrils
Gulls and other sea birds have a perpetual “runny
nose”
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Salt Gland of Marine Birds:
Salt is secreted into many
radial tubules, then flows into
central canal that leads to nose,
causing “Runny Nose”
27-44
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural and Functional Adaptations for Flight
Nervous and Sensory Systems



A bird’s nervous and sensory system must accommodate the problems
of flight and a visual lifestyle
Bird’s brain has well-developed cerebral hemispheres, cerebellum and
midbrain
Have good hearing and superb vision
 Best in the animal kingdom
 Although sense of smell and taste is poor in most

Ear is similar to that of mammals

External ear canal leads to an eardrum
Eye is similar to mammal eye, but it is larger for a
relative to body size


Less spherical and almost immobile


Has both rods and cones


27-45
Bird turns its head rather than eyes
Diurnal birds have more cones
Nocturnal birds have more rods
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
27-46
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Hawk Eye: Pecten nourishes retina
Cone cells on Foveae- 1.5 million for hawk, 0.2 million for human
Allows for better vision
27-47
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural and Functional Adaptations for Flight

Birds of prey have eyes directed forward


Many birds have two foveae or regions of detailed
vision



Provides better depth perception
Provides both sharp monocular and binocular vision
A hawk has eight times the visual acuity of a human
and can see a rabbit over a kilometer away
An owl’s ability to see in dim light is more than ten
times that of a human
27-48
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural and Functional Adaptations for Flight
Flight



27-49
History
Flight also provided rapid escape from predators
and ability to travel to better environments
2 hypotheses on the evolution of bird flight
 The “ground-up” (cursorial) hypothesis
 Based on running birds with primitive wings
to snare insects
 The “trees-down” (arboreal) hypothesis
 Has birds passing through tree-climbing,
leaping, parachuting, gliding, and finally
powered flight
 Feathers preceded flight and arose for
thermoregulatory purposes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural and Functional Adaptations for Flight

Flapping Flight





27-50
Requires a vertical lifting force and a horizontal
thrusting force
Greatest power is provided by downstroke
Primary feathers are bent upward and twist to a
steep angle of attack
On the upstroke, the primary feathers bend so
that upper surfaces twist to produce thrust
Powered upstroke is essential for hovering and
fast, steep takeoffs
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Normal Flapping Flight of Strong Flappers: the wings sweep downward and forward
fully extended. To begin upbeat the wing is bent, bringing it upward and backward.
27-51
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Hummingbirds can change direction instantly or hang motionless.
Its hinged at the shoulder by a swivel joint, and powered by flight muscles.
27-52
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural and Functional Adaptations for Flight

Basic Forms of Bird Wings
 Elliptical Wings
Birds that must maneuver in forested habitats
have elliptical wings
 Elliptical wings are slotted between primary
feathers to prevent stalling at low speeds, etc.
 The small chickadee can change its course
within 0.03 seconds

27-53
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
4 Basic Forms of Bird Wings
B. Long Migration birds
A. Slotted wing tip
Prevents stalling,
and quick maneuvering
27-54
D. High lift, slow speed,
Land Soarers
C. Soaring, poor
Maneuvering,
Strong to handle ocean
winds and currents
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural and Functional Adaptations for Flight

High-Aspect Ratio
Birds that feed on the wing or make long
migrations have high-speed wings
 These wings sweep back and taper to a slender
tip
 Reduces turbulence
 Flat in section and lack wing-tip slotting

27-55
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural and Functional Adaptations for Flight

Dynamic Soaring Wings




27-56
Albatrosses, gannets and other oceanic soaring birds
have wings with long, narrow wings
The high-aspect ratio of long, narrow wings lack wing
slots and allow high speed, high lift and dynamic soaring
They have the highest aerodynamic efficiency of any
design, but are less maneuverable
These birds exploit the highly reliable sea winds and air
currents of different velocities
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structural and Functional Adaptations for Flight

High-Lift Wings
Vultures, hawks, eagles, owls and other birds
of prey that carry heavy loads have wings with
slotting, alulas and pronounced camber
 Produces high lift at slow speed
 Many are land soarers


27-57
broad, slotted wings allow sensitive response for
static soaring
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Migration and Navigation
4 Basic Forms of Bird Wings
B. Long Migration birds
A. Slotted wing tip
Prevents stalling,
and quick maneuvering
27-58
D. High lift, slow speed,
Land Soarers
C. Soaring, poor
Maneuvering,
Strong to handle ocean
winds and currents
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Migration and Navigation
Migration




About half of all bird species migrate
Can move between southern wintering
regions and northern summer breeding
regions
Can exploit seasonal changes in abundance
of insects and avoid predators
Appearing one time a year prevents buildup
of specialized predators
27-59
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Migration and Navigation


Migration also expands living space and
reduces aggressive territorial behavior
Migration favors homeostasis, allowing birds
to avoid climatic extremes and food
shortages
27-60
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Migration and Navigation
Migration Routes




Most migratory birds follow established
north-south routes
Some use different routes in the fall and
spring
Some aquatic species make rapid journeys
Others such as warblers take 50–60 days to
migrate
27-61
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Migration:
14,000 miles
27-62
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Migration and Navigation



Smaller species migrate at night and
feed by day
Others are daytime migrants
Many birds follow landmarks


Some fly over large bodies of water
Some have very narrow migration lanes

27-63
Others have wide migration lanes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Migration and Navigation
Stimulus for Migration


Long days of late winter and early spring
stimulate development of gonads and fat
Long day length stimulates the anterior lobe
of the pituitary to release of pituitary
gonadotropic hormone

27-64
Gonadal growth, fat deposition, migration,
courtship, mating behavior, and care of young
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Migration and Navigation
Direction Finding in Migration



Experiments suggest birds navigate
chiefly by sight
Birds recognize topographical
landmarks and follow familiar migratory
routes
Research indicates they can navigate by
the earth’s magnetic field
27-65
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Migration and Navigation

Sun-azimuth Orientation


German ornithologists used special cages to show
birds navigate by sun at day and stars at night
Planetarium experiments revealed they use sun as a
compass




An internal clock tracks position
These experiments suggest use of the North Star as
an axis at night
Migration involves a combination of
environmental and innate cues
Natural selection culls individuals that make
errors

27-66
Only the best navigators leave offspring
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Bird maintains same relative
position to sun when placed in
experimental situation.
Birds use sun as a compass.
27-67
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Social Behavior and Reproduction
Cooperative Behavior



Sea birds often gather in huge colonies to
nest and rear young
Land birds, except for birds such as starlings
and rooks, tend to seek isolation for rearing
their brood
Birds that isolate during breeding may
congregate for migration or feeding
27-68
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Colony of Gannets (related to Pelican)- displaying social groups
27-69
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Social Behavior and Reproduction

Advantages for flocking together
 Mutual protection from enemies,
 Greater ease in finding mates,
 Less opportunity for an individual straying
during migration
 Mass huddling for protection against low
night temperatures during migration
27-70
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Social Behavior and Reproduction


Pelicans use organized cooperative behavior
to feed
Organized social interactions of birds are
most noticeable during breeding season

27-71
They stake out territory, select mates, build nests,
incubate and hatch eggs, and rear young
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Pelicans Feeding:
Work together form a
horseshoe to drive
fish together. Then
they plunge at same
time to scoop-out fish.
27-72
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Social Behavior and Reproduction
Reproductive System

Testes are very small until the approach of
the breeding season




May then enlarge 300 times
Before discharge, sperm are stored in a
greatly enlarged seminal vesicle
Males of most species lack a penis
 Mating involves bringing cloacal surfaces
in contact
In most birds, left ovary and oviduct develop
and right ovary and oviduct degenerate
27-73
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Albatrosses Mating: Press Cloaca together
27-74
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Social Behavior and Reproduction





Expanded end of the oviduct receives
discharged eggs
Special glands add albumin or egg white to
the egg as it passes down the oviduct
Farther down oviduct, the shell membrane,
shell, and shell pigments are also secreted
Fertilization takes place in the upper oviduct
before albumin and shell are added
Sperm remain alive in the oviduct for many
days after a single mating
27-75
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Right Side of reproductive tract
degenerates, leaving only
left side. Fertilization occur
in upper oviduct and albumin
and shell membrane are added
several hours later in lower
oviduct and uterus
27-76
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Social Behavior and Reproduction
Mating Systems

Over 90% of bird species are monogamous



Recent DNA analyses have shown many
passerine species frequently are “unfaithful,”
engaging in extra-pair copulations


Only mate with one partner each breeding season
In a few species, such as swans and geese,
partners are chosen for life
Nests of many of these species may contain 30%
of young with fathers other than attendant male
In monogamous birds, both male and
females are equally adept at most aspects of
parental care
27-77
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Social Behavior and Reproduction

Bird Territories
 A male sings often to announce his
presence to females and drive away males
 Females wander about to select a male
that offers the best chance of reproductive
success
27-78
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Social Behavior and Reproduction

Some birds are polygamous
Individuals mate with two or more partners
each breeding season
 Polygyny

Most common form of polygamy
 One male mates with many females

Competition for females is intense and
females appear to choose the dominant
male for mating
 Polyandry in which a female mates with
several males and the male incubates the
eggs, is relatively rare in birds

27-79
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Male Grouse: Mates with many females
27-80
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Social Behavior and Reproduction
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

27-81
Rarely the male has equal or sole duties
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Anna’s Hummingbird: Mother cares for young alone
Hummingbird eggs are size of peas.
27-82
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Social Behavior and Reproduction





Some birds merely lay eggs on bare ground
or rocks
Others build elaborate nests using mud,
lichens, brush, etc.
Nests are often carefully concealed from
enemies
Woodpeckers, chickadees, bluebirds and
others nest in tree hollows and other cavities
Cuckoos and cowbirds are nest parasite

27-83
Lay eggs in other bird’s nests
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Social Behavior and Reproduction


Precocial birds are able to feed and run or
swim as soon as they are hatched
Altricial birds are naked and helpless at birth
and must be fed in the nest for a week or
more


27-84
Nesting success in altricial birds is very low
 Sometimes barely 20% of nests produce young
Causes of nesting failure include predators, nest
parasites and other factors
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
27-85
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Bird Populations
Factors
 Bird populations vary in size from year to
year
 Birds of prey may cycle with the food supply



Snowy owl populations vary with the rodents they
eat
When food supplies crash, birds may move
elsewhere to locate alternative food
Humans have introduced birds to new
regions

27-86
The starling and the house sparrow are both
abundant now in the United States
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Starling Bird - 120 birds introduced to New York City’s Central Park in 1890.
Today 200 million starlings: Due to great reproductive potential, and omnivorous.
27-87
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Bird Populations

Since the dodo went extinct in 1695
(flightless bird)


More than 80 bird species have also become
extinct due to human influence
Causes of bird extinction include habitat
destruction and hunting
Songbirds have declined:
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.


Habitat destruction, house cats increased, etc.
Dodo Bird
27-88
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Largest of All Living Birds
African Ostrich
27-89
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
27-90