http://www.rit.edu/~vertzo/Pigeon/PigeonPages/Home.html
http://www.bioweb.uwlax.edu/zoolab/Table_of_Contents/Lab-9b/Pigeon/pigeon.htm
Bird Dissection
INTRODUCTION: The bird is a
vertebrate whose body plan is adapted to its requirements for flight. For example, the skeletal system is
lightweight and very strong. The flight
muscles of the chest may make up one fifth of the total mass of a bird's
body. Birds have extremely great energy
requirements because of their high metabolic rate. The unique air sacs of their respiratory
system provide them with a continuous supply of oxygen. In line with their needs for a streamlined,
lightweight body, birds' reproductive organs are small and inactive for most of
the year. During the breeding season,
however, the male and the female reproductive organs increase greatly in
size.
PURPOSE: In this investigation, you will be exploring
some of the unique structural features of a bird through a dissection. The bird under study, found in great numbers
in North America, may be either a pigeon or a sparrow.
CLASSIFICATION: Kingdom: Animalia Phylum: Chordata Class:
Aves
MATERIALS NEEDED: preserved specimen / probe /dissecting tray / forceps /
scissors / hand lens / scalpel or
razor blade
PROCEDURE: Obtain a preserved bird. Place the ventral side up in a dissecting
tray.
- Spread
out one wing to that the various types of feathers are visible. Locate the
primary feathers which are attached to the bones of the 'fingers' and the
wrist. Find the shorter secondary
feathers which are attached to the ulna.
Finally, identify the smaller scapular feathers, which grow from
the shoulder. Primary, secondary,
and scapular feathers are all flight feathers and are covered by small,
shingled covert feathers.
- Locate
the ulula feathers, which are attached to one of the bones of the
"fingers". These
feathers, which are similar to the slots on the leading edge of an
airplane wing, allow for slower flight.
- Draw
and label the main kinds of feathers in the wing of your preserved
bird.
- Pull
out one of the primary feathers and examine it with a hand lens. Locate the long, slender, hollow
shaft. From the shaft, you will
note that barbs extend outward at an angle of about 45 degrees. With your fingers, gently pull apart the
barbs. Notice that they are formed
of still smaller barbules with interlocking hooks.
- Examine
the barbs and the barbules with your hand lens.
- Draw
and label the major structures of the feather as you see it with the hand
lens.
EXAMINE THE PIGEONS'SHEAD
- Examine
the pigeon's head. Look closely at
the eye, with its moveable upper and lower lid. Gently pull the lids back to that you
can see the nictitating membrane in the corner of the eye. At the upper end of the beak is a slitlike
nasal opening. Just behind this
opening, locate a white structure called the cere, which is at the
juncture of the beak and the head.
Just below and slightly behind the eye, look for the external ear
opening.
- Carefully
open the pigeons beak and look inside the mouth.
- Does
the bird have any teeth?
- How
does the bird grind up its food?
EXAMINING THE
MUSCLES
- Place
the pigeon ventral side up in the dissecting pan. With a pair of forceps, lift the skin at
the opening just above the tail.
- Make
a shallow cut through the lifted skin with a scalpel.
- Insert
the rounded edge of the scissors into this small opening and cut through
the skin along a midventral line, from the cloacal opening to just under
the head.
- Make
4 digital cuts from the midventral incision; two into the wing areas and
two into the leg areas.
- Fold
back the layers of the skin so that you can look into the body
cavity.
- Locate
the two large pectoralis muscles, which are attached to the keel.
- Carefully
cut through the one layer of muscle and peel it back to show a second
layer beneath it. The lower layer
is called the pectoralis minor muscle.
Both pectoralis muscles (major and minor) are the flight muscles.
- Note
their size and mass.
- Using
your scissors, carefully cut through the skin of the left leg. Gently pull back the skin so that you
can see the muscles of the leg.
NOTE: You may have to cut through the connective tissue to free the
muscle tissue from the skin. As you
look at the muscles of the leg, locate the iliotibialis muscle, which is
the broad, heavy muscle of the upper leg.
Identify the long gastrocnemius muscle of the lower leg. Using your probe, move aside the layers of
muscle in the lower leg so that you can see the fibula beneath the muscle.
- Study
the skin on the pigeons feet. Note
its texture and the presence or absence of feathers. Look at the tops of the pigeons
toes.
DIGESTIVE
SYSTEM
For an animal to use
food as fuel, it must digest the food - break it down small enough to be
absorbed into the bloodstream - and get rid of the waste products. A bird's gut
looks much like your own, but there are some differences. Many seed and
grain-eating birds have a crop connected to the esophagus. The expandable crop
allows birds to quickly gather and store a large amount of food, then retreat
to safety to digest it.
- Using
a scalpel, cut through all the connective tissue holding the pectoral
muscles in the keel. Completely lay
back the pectoral muscles so that the keep is visible.
- Using
a pair of scissors, cut through the keel just to the left of the
midventral line. NOTE: It does not
matter if you crack the keel bone.
Your purpose in cutting it is to reveal the internal organs. Remove any connective or fatty tissue
that is still clinging to the organs of the digestive system.
- Locate
the thin-walled flabby tube or esophagus, in the neck of the bird. This tube is the first part of the
digestive system that is visible to you.
Of course, the food enters the mouth and then passes down into the
esophagus. The lower part of the
esophagus widens into a large, hard object called the crop.
- Below
the crop is the true stomach, which has two part. The upper part is called the
proventriculus. In this part of the
stomach, digestive enzymes secreted by glands break down food that has
passed into the stomach. The lower
part of the stomach is called the gizzard.
This organ has strong muscular walls that can churn up the
food. The gizzard may contain small
stones or pebbles.
- Locate
the long intestine which follows after the gizzard. Look for the large, lobed liver, which
overhangs the intestine. If you
separate the coils of the intestine, you should be able to see the
pancreas. Look for the pancreatic
ducts which pass from the pancreas to the small intestine.
- Examine
the lower end of the intestine. You
should be able to find two saclike caeca.
The caeca are at the juncture of the intestine and the rectum.
- Locate
the cloaca which is the common exit of the digestive tract, reproductive
organs, and urinary organs. You may
be able to find the ducts leading from the kidneys to the cloaca.
- A bird has two stomachs (we have one) to
digest its food in record time. In four hours, a Spur-winged Goose can
digest the same meal that it takes a rabbit 24 hours to digest. In the
upper stomach, the proventriculus, food is broken down with digestive
enzymes.
The lower stomach, the ventriculus, or gizzard, is a tough, muscular organ
which crushes and grinds up the food, just like our teeth do for us.
Remember a bird has no teeth, so it swallows food whole. Birds that eat
plants and seeds have more powerful gizzards than meat and fish eaters.
Many birds swallow grit or gravel to help the gizzard break down food.
RESPIRATORY SYSTEM
AND HEART
Lungs
exchange oxygen and carbon dioxide between the blood and air. Bird lungs are
smaller than those of mammals, yet they are part of the most efficient respiratory
machinery known in vertebrates. Even with this efficient respiratory system,
birds breathe rapidly during flight - up to 450 breaths per minute for a
pigeon.
Unique to birds are air sacs. Air sacs act as a
bellows to suck air into the body, then circulate it in a one-way flow through
the lungs - giving the lungs a constant flow of fresh air.
The nine air sacs also act as a cooling system
since birds do not have sweat glands. They contribute to stability in flight by
lowering the center of gravity and act as shock-absorbers in diving birds, such
as Brown Pelicans. During courtship, male grouse inflate special air sacs on
their chests like brightly colored balloons to attract a mate.
HEART
A bird's heart is much
like yours - a four chambered muscle that pumps blood throughout the body. A
bird's heart weighs up to twice as much as that of a mammal of equal size
because flying is strenuous. Energy-hungry muscles need a bigger, faster
beating heart to send them plenty of oxygen and nutrients. Smaller birds and
mammals lead fast-paced lifestyles and generally have faster heart rates than
large ones. Hummingbird 600 beats per
minute at rest, Pigeon 200 beats per minute at rest, Ostrich 65 beats per
minute at rest, Human 70 beats per minute at rest.
- In
the throat region, locate the trachea (windpipe) which is ventral to the
esophagus, except where the crop bulges over it. Run your fingers over the surface of the
trachea. You should be able to feel
the tracheal rings which provide form to the wall. Trace the trachea down to its lower end,
where there is a somewhat swollen chamber.
This chamber, which includes specialized internal membranes, is
called the syrinx. The syrinx, an
organ found only in birds, is the organ from which birds produce their
various calls and songs.
- Trace
the syrinx down to its base, where it divides
into two smaller tubes called bronchi.
Each bronchus leads to a lung.
The lungs are relatively small organs. Look for two flattened structures
pressed against the ribs and lying on either side of the vertebral
column. Unique to the birds is a
system of air sacs that extend out from the lungs.
- Look
for six pairs of air sacs - a pair of abdominal, two pairs of thoracic,
one pair of subscapular, one axillary pair, and one cervical pair. These sacs squeeze into any available
space between the other internal organs.
- Look
for the pigeon’s heart in the center of its chest cavity. It will probably be about 3cm long. Look for the major vessels entering and
leaving the heart. Trace the blood
vessels that join the heart and the lungs.
- Using
your scalpel, carefully make a lengthwise cut through the heart, starting
at the lower lip and moving toward the anterior end. The cut should separate the heart into a
ventral part and a dorsal part. You
should now be able to see the chambers of the bird's heart.
UROGENITAL
SYSTEM
- In
your study of the digestive system, you probably came across the kidneys.
You will look at the kidneys and other parts of the urinary system a
little more closely now. Locate the
dark, three-lobed kidneys. They are
just below the lungs and fit into a depression in the dorsal wall of the
bird.
- Look
for narrow ducts, or ureters, leading from the kidney to the cloaca. Note that the bird has no urinary
bladder. During most of the year,
the genital system of the bird is much reduced in size. This reduced size reduces the total mass
the bird must carry around. You
will probably have a male or female bird with its reproductive organs in
this inactive stage. If you have a
male bird, look for two white testes, the male reproductive organs. The testes are ventral to the kidneys
and may be slightly anterior to them.
Locate the two narrow sperm ducts that lead from the testes to the
cloaca. If you have a female
pigeon, look for the ovary on the left side of the body. The ovary is in about the same position
as the left testis would be.
- Locate
the flaring end of the oviduct, which should open close to the ovary. Trace the oviduct down to its posterior
end, which will empty into the cloaca.
The size of the ovary and oviduct will vary, depending on whether
the bird died during the breeding season or during the reproductively
inactive period.
- Draw
the urogenital system of the bird.
Label the kidney, ureter, testis, sperm duct, ovary, and oviduct in
your drawing.
BIRD BRAIN
Birds are known for their fast reactions, balance,
coordination and instinctive behavior. Bird brains are relatively larger than
those of reptiles but smaller than those of mammals. Birds are not known for
reasoning abilities however, some birds do have significant learning abilities,
such as parrots trained to talk or do tricks.