prof. Nanda Bhupal Jagtap (Dept.of Zoology) Dapoli Urban Bank Senior Science College Dapoli District Ratnagiri Maharashtra.

1. Respiratory System of Pigeon
Prof.Nanda .B.Jagtap (Dept.Of.Zoology)
Dapoli Urban Bank Senior science college Dapoli
Dist.Ratnagiri (Maharashtra)

2. The flight activity requires a continuous and abundant supply of oxygen, therefore, the respiratory
system of birds is highly developed and well differentiated. Respiration is pulmonary and respiratory
organs are simple. Muscular diaphragm in birds is lacking. The respiratory system includes the
respiratory tract, the respiratory organs or lungs and the air sacs.
o Respiratory System
• Respiratory Tract:
The respiratory tract includes nares, nasal sacs, glottis, larynx, trachea and syrinx.
i. Nares, Nasal Sacs and Glottis:
1. The external nares or nostrils are a pair of slit-like oblique apertures occurring at the base of upper
beak and are overlapped by a swollen sensitive skin.
2. The external nares open into short olfactory or nasal sacs which remain communicated to the
pharynx by internal nares or choanae.
3. Glottis is a slit-like aperture, which is present on the floor of the mouth cavity and near the base of
the tongue. It leads into the next part called trachea.

3. ii. Larynx
1. The larynx is an expanded, voiceless chamber which occurs at the anterior most margin of trachea
and is greatly reduced in birds.
2. The larynx of birds does not function as a sound producing organ. Larynx opens into a long trachea.
iii. Trachea:
1. This elongated tube begins from glottis and runs along the neck region along the ventral side of the
oesophagus. The trachea is composed of complete bony tracheal rings.
2. This chamber is supported by a cricoid cartilage (which is composed of four pieces) and one pair of
arytenoid cartilages. In birds, the larynx does not function as voice box.
iv. Syrinx:
1. The syrinx is a vocal organ found only in birds. It is present at the junction of trachea and paired bronchi.
2. The mucous membrane of the syrinx constitutes a pad-like thickening and is provided with several
muscles and membranes. The syrinx is actually the voice box. The syrinx is the characteristic organ of
pigeon and many other flying birds.

4. • Respiratory Organs or Lungs:
1. The lungs are small in size in comparison with that of the body. These are paired pink-coloured organs.
The lungs are spongy organs with little elasticity.
2. The dorsal surface of the lungs is fitted closely with the interspaces of ribs and lacks the peritoneal
covering, i.e., pleura is absent on the dorsal side.
3. The ventral wall has a compact fibrous tissue sheet called pleura or pulmonary Apo neurosis. The wall
of the pleura has special fan shaped costopulmonary muscles which originate from the joints of verte-
bral and sternal ribs. The alveolar lining is formed by the ramification of tertiary tubules with the
distribution of blood vessels.

5. • The Air Sacs:
1. The air-sacs are bladder-like structures. These are formed by the dilation of the mucous membrane of
the bronchus.
2. The air-sacs are thin-walled membranous sacs and are devoid of blood vessels. Following air-sacs are
present in the body of pigeon and all of them remain in communication with the pneumatic cavities of
bones. There are nine major and four accessory air- sacs in pigeon
Air Sac

6. • Role of air-sacs:
The air-sacs play an important role in the life of flying birds. The air-sacs are not provided with capillary network,
so they are not directly respiratory in function. Besides, these sacs are essential components for aerial life.
1. Act as balloons: When the air-sacs are inflated due to intake of warm air, the specific gravity of the body is
lowered to a considerable extent. As the warm air is lighter than ordinary air, the retention of such air inside the
air-sacs makes the body considerably lighter.
2. Function as ballast: The air-sacs are so nicely arranged on the two sides of the body that proper centre of gravity
is established for balanced flight.
3. Regulate and maintain body temperature: Retention of warm moist air inside the air- sacs helps to regulate
and maintain the body temperature.
4. Act as resonator: The pitch of the sound is controlled to some extent by the forceful expulsion of the air from the
air-sacs which act as resonator.
5. Lessen mechanical friction: A placement of air-sacs reduces mechanical friction to a large extent and increases
the flexibility of the wings during flight.

8. • Mechanism of respiration:
1. The unique feature of avian respiration is the double supply of oxygenated air to the surface of lungs for improved
aeration. For this reason, respiration in birds is called double respiration.
2. Two cycles of inspiration and expiration are required for a single volume of gas to move through the respiratory system.
3. During the first inspiration, the sternum is lowered, and the lungs and the air-sacs are expanded.
4. The fresh air rushes through trachea and bronchi into the posterior air sacs. During the first expiration, the sternum is
raised and the air from the posterior sacs goes to the Para bronchi and air capillaries. At second inspiration, air from the
Para bronchi goes to the anterior air sacs and, on the second expiration, the air is expelled outside.
5. the residual air remains inside the air sacs and in the smaller branches of the bronchi. As the aeration of blood is
complete in pigeon, it thus increases the respiratory efficiency to yield extra energy.
6. During flight, both inspiration and expiration are caused by the movement of pectoral muscles.
7. At the time of rest, inspiration is caused mostly by the activities of intercostal muscles and expiration by the movement
of abdominal muscles.