Respiratory System of Birds: Anatomy and Function Drs. Foster & Smith Educational Staff

Differences between avian and mammalian respiration

Respiration in birds is much different than in mammals.

Birds have a larynx, but it is not used to make sounds. Instead, an organ termed the"syrinx" serves as the "voice box."

Birds have lungs, but they also have air sacs. Depending upon the species, the bird hasseven or nine air sacs. The air sacs include:

Two posterior thoracicTwo abdominalTwo anterior thoracicTwo cervical (these are not present in some species)One interclavicular

The air sacs of birdsextend into thehumerus (the bonebetween the shoulderand elbow), the femur(the thigh bone), thevertebrae and even theskull.

Birds do not have adiaphragm; instead,air is moved in andout of the respiratorysystem throughpressure changes inthe air sacs. Musclesin the chest cause thesternum to be pushedoutward. This createsa negative pressure inthe air sacs, causingair to enter therespiratory system.Expiration is notpassive, but requirescertain muscles tocontract to increasethe pressure on the airsacs and push the airout. Because thesternum must moveduring respiration, itis essential that it isallowed to movefreely when a bird isbeing restrained.Holding a bird "tootight" can easily causethe bird tosuffocate.

Because birds have airsacs that reach intothe bones, and have nodiaphragm,respiratory infectionscan spread to the abdominal cavity and bones.

Bird lungs do not expand or contract like the lungs of mammals. In mammalian lungs, the exchange of oxygen and

Air Sacs of a Bird

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carbon dioxide occurs in microscopic sacs in the lungs, called 'alveoli.' In the avian lung, the gas exchange occurs inthe walls of microscopic tubules, called 'air capillaries.'

The respiratory system of birds is more efficient than that of mammals, transferring more oxygen with each breath.This also means that toxins in the air are also transferred more efficiently. This is one of the reasons why fumes fromteflon are toxic to birds, but not to mammals at the same concentration.

When comparing birds and mammals of similar weight, birds have a slower respiratory rate.

Respiration in birds requires two respiratory cycles (inspiration, expiration, inspiration, expiration) to move the airthrough the entire respiratory system. In mammals, only one respiratory cycle is necessary.

Respiratory cycle of a bird

During the first inspiration, the air travels throughthe nostrils, also called nares, of a bird, which arelocated at the junction between the top of the upperbeak and the head. The fleshy tissue that surroundsthem, in some birds, is called the cere. As inmammals, air moves through the nostrils into thenasal cavity. From there it passes through the larynxand into the trachea. Air moves through the trachea tothe syrinx, which is located at the point just beforethe trachea divides in two. It passes through thesyrinx and then the air stream is divided in two as thetrachea divides. The air does not go directly to thelung, but instead travels to the caudal (posterior) airsacs. A small amount of air will pass through thecaudal air sacs to the lung.

1.

During the first expiration, the air is moved from theposterior air sacs through the ventrobronchi anddorsobronchi into the lungs. The bronchi continue todivide into smaller diameter air capillaries. Bloodcapillaries flow through the air capillaries and this iswhere the oxygen and carbon dioxide are exchanged.

2.

When the bird inspires the second time, the airmoves to the cranial air sacs.

3.

On the second expiration, the air moves out of thecranial air sacs, through the syrinx into the trachea,through the larynx, and finally through the nasalcavity and out of the nostrils.

4.

Respiratory Cycle of a Bird

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Unauthorized use of any images, thumbnails, illustrations, descriptions, article content, or registered trademarks of Foster & Smith, Inc. is strictly

prohibited under copyright law. Site content, including photography, descriptions, pricing, promotions, and availability are subject to change without

notice. These restrictions are necessary in order to protect not only our copyrighted intellectual property, but also the health of pets, since articles or

images that are altered or edited after download could result in misinformation that may harm companion animals, aquatic life, or native species.