Domestic Fowl (Gallus domesticus)
Classification of Domestic fowl
Phylum: Chordata
Sub-phylum: Vertebrata
Class: Aves
Order: Galliformes
Domestic fowls are 'warm blooded' or homoiothermic (constant temperature); that means they maintain their body temperature at a constant level and above that of their surroundings.
Structure of Domestic fowl
The body consist of a head, trunk and tail. The head is small and round. The skull is extended into two strong pointed, horny structures called beak. It has a pair of slit-like nostril, a pair of eyes, eyelids and a nictitating membrane. Behind each eye is the ear opening hidden by feathers. It has a red fleshy skin on the head called a comb and a pair of hanging fleshy skin below the beak called wattles. The wattle and comb are more prominent in male than female. The head is covered with feathers except the beak, comb and wattle.
The head is connected to trunk by a long neck. The trunk bears fore-limbs and hind-limbs. The forelimbs are modified to form wings. The legs and toes are covered with overlapping scales. Each leg has four digits with sharp, curved claws, three are directed forward and one back. The tail is short and covered with quill feathers and has oil glands called preen gland under it. The preen glands produces oil which is used to preen or groom feathers to keep them glossy and waterproof.
Feathers
The feathers are produced from the skin which is loose and dry. They are made up of protein called keratin. Feathers consist of a shaft or rachis with rows of fine filaments on each side called barbs. The barbs themselves have further rows of finer filaments called barbules.
Functions of feathers
· They keep the body temperature constant
· They prevent wetting of skin (repelling water
· They are used for sexual display during courtship
· They protect the body against mechanical injury
· It gives streamlined body shape for efficient flight
Types of feathers
□ Flight or quills feathers: are broad and flat and offer resistance to the passage of air. It consists of a flexible shaft running down the center. The lower part of the shaft is hollow and forms the quill. The quill has a hole at the posterior end called inferior umbilicus, which contains a piece of papilla tissue. The base of the quill is embedded in a small pit in the skin called the follicle. The shaft bears a large number of a filaments called barbs. Each barb bears on each side a row of small branches called barbules. The barbules of the upper row have hooks and those on the lower row have grooves or ridges. The hooks on one set of barbules interlock with ridges on the other set to form a stiff barb called the vane. The quill feathers are found on the wing and tail. They are used for flying, steering and balancing. They are also used for sexual display during courtship.
□ Covert or contour feathers: are small but similar to the quill feathers in structure. It covers the entire body except the legs. The barbs and barbules of the contour feathers are organized in a regular way forming a smooth, water-resistant cover. They keep the body warm and also used in sexual display during courtship.
□ Down feathers: the barbs and barbules are loose and fluffy. The barbules lack hooks and ridges. They trap an insulating layer of air close to the body and so reduce heat losses.
□ Filoplumes: are small, hair-like and found all over the body. It consists of slender shaft with a tuff of barb at the end. Its function is not known yet.
Differences between Contour and Down feathers
Contour feathers | Down feathers |
Large or short feathers | Small or short feathers |
Stiff shaft or rachis | Flexible shaft |
Large quill | Short quill |
Lower half of barbs are fluffy | Barbs are fluffy |
Visible inferior umbilicus | Interior umbilicus not visible |
Life Processes of Domestic fowl
Nutrition in Domestic fowl
It is omnivorous. It feeds on seeds, insects, worms and plant materials such leaves. The sharp, strong claws are used to scratch the soil in search of food, which is picked with the sharp pointed beak. The food is swallowed through the esophagus into the crop, where it is temporary stored. The food enters the proventriculus, the first part of the stomach, and digestive juices are secreted to digest the food. The food then enters the gizzard, the second stomach. Churning and mechanical breakdown of food takes place in the gizzard. The presence of small fine stones in the gizzard aids in mechanical grinding of the food. The food enters the intestine for further breakdown and absorption to occur. The caeca absorb water from the food. The rectum empties the undigested food into the caeca to be eliminated as feces.
Movement in Domestic fowl
The flight of a bird can be divided into flapping, and gliding or soaring.
□ Flapping: the pectoralis major muscle contracts, pulling the fore-limb down. The resistance of the air to the wing produces an upward reaction on the wing which create a force to lift it as a whole. In addition to the lift, forward momentum is provided by the slicing action of the wing. In the down-stroke the secondary feathers provide much of the lifting force and the primaries most of the forward component. The up-stroke of the wing is much more rapid than the down-stroke. The pectoralis minor muscle contracts and raises the wing. The wing is bent at the wrist during the up-stroke thus reducing the resistance.
□ Gliding or Soaring: In gliding flight the wings are outspread and used as aerofoils, the bird sliding down a 'cushion' of air, losing height and gaining forward momentum. Sometimes upward thermal currents or intermittent gusts of wind may be used to gain height without wing movements; in seagulls and buzzards for example.
Features which adapt the bird for flying
□ The large surface area of wing feathers enables the bird to fly.
□ The streamlined body shape enables the bird fly through the air with little resistance.
□ Tips of the wing/tail feathers controls steering.
□ Large pectoral muscles for depressing the wings.
□ Keel-like extension from the sternum allows attachment of the pectoral muscles.
□ A rigid skeleton giving a firm framework for attachment of muscles concerned with flying movements.
□ Hollow bones, which reduce the bird's weight.
□ The tail stabilizes the bird in flight and important in braking and landing.
□ Eyes placed at the side of the head enables the bird to have wide acute vision
Reproduction in Domestic fowl
o Courtship and Mating: a rooster or cockerel may dance in a circle around or near a hen called "a circle dance". It lowers the wing and display colored feathers. The male mounts the female, applies his reproductive openings to hers and passes sperm into her oviduct. Fertilization is internal.
o Egg laying: The fertilized egg is enclosed in a layer of albumen and a shell during its passage down the oviduct and is finally laid in the nest. Usually, one egg is laid each day and incubation does not begin until the full clutch or group has been laid.
o Incubation: The female is responsible for incubation, keeping the eggs at a temperature approximating to her own. It covers them with her body and press them against her brooding patches. At this temperature, the eggs develop and hatch in a week or two.
o Development: The living cells in the egg divide to make the tissues and organs of the young birds. The yolk provides the food and the albumen is a source of both food and water. The eggshell and shell membranes are permeable to air. Oxygen diffuses into the air space and absorbed by the network of capillaries which spread out over the yolk and over a special sac called the allantois. The blood carries the oxygen to the embryo. Carbon dioxide is eliminated by the reverse process through the eggshell. When the chicks are fully developed, they break out of the shell by using their beaks.
o Parental care: The chicks are covered with down feathers and can run about soon after hatching. They peck at objects on the ground and stay close to the hen, responding to her calls by taking cover. The hen covers them with the body and wings and protect them against predators such as cats and hawks.
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Function of the Parts of Egg
□ The amnion is a fluid-filled sac which suspends and protects the embryo.
□ The allantois stores excretory products and also carries oxygen to the embryo in its numerous blood vessels.
□ The yolk sac shrinks as the embryo uses up its food store and is absorbed into the body at hatching.
□ The yolk provides proteins and lipids (fats) for developing embryo.
□ The albumen provides proteins and water for developing embryo.
□ The chalaza is a twisted strand of dense albumen, holds the yolk in place.
□ The shell and egg membrane are permeable to air and protect the embryo.
Differences between Birds and Reptiles
|
Bird |
Reptile |
|
Body is covered with feathers |
Body is covered with scales |
|
Wings present |
Wings absent |
|
Mouth modified into beak |
Mouth is terminal and wide |
|
Teeth absent |
Teeth present |
Similarities between Birds and Reptiles
· Nictitating membrane protecting the eyes
· Limbs with claws
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