Zoology Name: ____________________________________

Edited by C. Johnson 1

PIGEON 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.

MATERIALS NEEDED: preserved specimen /probe/dissecting tray/forceps/scissors/hand lens/scalpel

PROCEDURE:

EXTERNAL OBSERVATIONS

1. Obtain a preserved bird and rinse it with tap water. Place the ventral side up in a dissecting tray. Spread out one wing to that the various types of feathers are visible.

Use your “Bird Feather Types, Anatomy, Growth, Color, and Molting” reference worksheet as a guide to study the anatomy of your pigeon’s feathers.

2. 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.

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EXAMINE THE PIGEON’S HEAD

1. Examine the pigeon's head. Look closely at the eye, with its moveable upper and lower lid.

2. 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 slit-like 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.

Morphological Features:

1. Bill length (culmen): The distance from the tip of the upper mandible to the end of the culmen at its intersection with the cere, or forehead.

2. Wing Length: The wing chord is measured from the bend of the wing (wrist) to the tip of the longest primary using dividers. The flattened wing length is measured by pressing the wing down on a ruler from the wrist to the tip of the longest primary.

3. Tail Length: The distance from the tip of the longest RECTRIX (longest tail feather) to the point where it emerges from the skin.

4. Tarsus length: The distance from the heel joint (tibiotarsus-tarsometatarsal joint) to the point of the tarsometatarsal joint at the base of the middle anterior toe.

5. Total length: The distance from the tip of the bill to the tip of the longest rectrix when the bird is placed on its back with the head tipped back parallel to the table surface. Should be reported for fresh specimens only, not museum specimens.

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6. Wing span or extent: The tip-to-tip distance of the longest primaries when the bird is placed on its back with wings outstretched. Should only be reported for fresh specimens.

*Label on this drawing the name of its measurement:

SKINNING/DEFEATHERING

1. Before skinning and plucking your bird, hold one wing out to its full extent and feel the flap of skin between the humerus and the radius-ulna area. This is the PATAGIUM (like the skin membrane part of a wing, like a bat’s membrane-like wing). There is a tendon at the anterior (front) border of the patagium. Be very careful not to cut this tendon while you are removing the skin of the bird.

2. Look for the UROPYGIAL GLAND (“preening gland”) on the bird's back, just above where the tail feathers insert. This gland, usually a small lobe, produces oil used for PREENING the feathers.

EXAMINING THE MUSCLES

1. Make 4 digital cuts from the mid-ventral 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.

2. Locate the two large PECTORALIS MUSCLES, which are attached to the KEEL (shaded in picture to the right). A keel in bird anatomy is an extension of the sternum (breastbone) which runs axially along the midline of the sternum and extends outward, perpendicular to the plane of the ribs. The keel provides an anchor to which a bird's wing muscles attach, thereby providing adequate leverage for flight. Keels do not exist on all birds; in particular, some flightless birds lack a keel structure.

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3. 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. Observe these muscles:

Pectoralis--The largest and most powerful muscle in the bird. It is visible as a large mass of muscle fibers originating on the sternum and having its fibers converging and inserting on the humerus. Find this insertion. This muscle serves to depress the wing.

4. 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.

5. Study the skin on the pigeon’s feet. Note its texture and the presence or absence of feathers. Look at the tops of the pigeon’s toes.

DIGESTIVE SYSTEM (see “Pigeon Dissection Guide” numbered outline for basic information)

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.

1. Using a scalpel, cut through all the connective tissue holding the pectoral muscles in the keel.

2. 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.

3. 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. The crop is where food is stored until parents can feed their young. Crop milk (a mixture of lipids and proteins) is also secreted here for baby food!

4. 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 (right after the crop). In this part of the stomach, digestive enzymes secreted by glands break down food that has passed into the stomach.

5. 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. The gizzard may contain small stones or pebbles to help “grind” the food.

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6. Locate the 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.

7. 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.

8. 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.

RESPIRATORY SYSTEM, AIR SACS, & HEART

See your “Respiratory System of a Bird” packet for more information. 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.

1. Unique to birds are AIR SACS. Air sacs act as a bellows to suck air into the body, and then circulate it in a one-way flow through the lungs - giving the lungs a constant flow of fresh air.

2. 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.

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3. The lungs of birds feature out-pocketings filled with air which extend between various organs and penetrate certain bones; they have few blood vessels and no respiratory surfaces. The sacs are transparent and noticeably thin-walled, resembling soap bubbles.

4. To be seen, the respiratory system needs to be artificially inflated. Cut the trachea (windpipe) in the neck region, insert a pipet and blow through it (see instructions below). The lungs and air sacs should become distended and more prominent. There are 9 air sacs.

5. Make a mid-ventral incision through the body wall for the entire length of the abdominal

cavity. Pull the internal organs carefully to one side and blow into the trachea as described above.

6. If the dissection has been done correctly to this point the abdominal AIR SAC should be visible. It will resemble an asymmetrical soap bubble. See how many other sacs you can find and identify (they can be very difficult to see). If you have cut the respiratory system at any point previously, the air sacs will not inflate and will not be visible.

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.

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1. 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 (“Syrinx = Sing”).

2. 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.

3. 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.

4. 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 (looks like this…)

CHICKEN HEART Human Heart

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UROGENITAL SYSTEM

1. 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.

2. 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. The right ovary in birds is nonfunctional.

3. 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.

4. Each kidney is made up of three lobes.

The ureters emerge from the rear border of the anterior lobe, pass over the ventral surface of the two posterior lobes, and then back to the “urodaeum” (uro-genital chamber). On the anterior ventral surface of each kidney is a small yellowish ADRENAL GLAND.

5. The TESTES in the male are two white ovoid bodies (variable in size with breeding condition) lying on the ventral surface of the anterior lobe of the kidney. Convoluted and narrow VASA DEFERENTIA lying lateral to the ureters connect the testes to the urodaeum then cloaca.

6. In most female birds there is only the left ovary and oviduct lying on the ventral side of the left kidney. The ovary is irregular in shape due to the different sizes of ova.

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HOW EGGS FORM

MAGNUM – receives first layer of albumen here

ISTHMUS – egg and shell membranes and more albumen added here

SHELL GLAND – albumen, shell, and pigments added here

Ovulation to laying = 24 hours!

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PIGEON PRE-LAB QUESTIONS! *DUE THE DAY OF YOUR DISSECTION*

1. What phylum are birds in? Name 3 other classes of animals in the same phylum.

2. Does the bird have any teeth? How does the bird grind up its food?

3. What muscles are the main flight muscles?

4. If you were eating a chicken thigh, what muscles would you be eating?

5. What is the function of the keel on the sternum?

6. What differences in digestive systems are there between you and a bird?

7. What is the top part of the stomach called? What is the lower part of the stomach called?

8. What did you find in the lower part of the stomach?

9. How many air sacs were there in your pigeon? What is the function of the air sacs?

10. Is a bird’s heart larger or smaller than other animals of the same size? Why do you think this is?

11. What happens to the size of the reproductive organs during breeding season?