Circulatory System of Birds: Functions and Structure

He Circulatory system of birds Is composed of the heart (four cavities, similar to mammals), arteries and veins that carry nutrients, oxygen, carbon dioxide, metabolic waste, hormones and temperature.

This model of circulatory system is quite efficient, since it allows the birds to satisfy their metabolic needs to be able to fly, run, swim or dive. This system not only distributes the oxygen contained in the blood to the cells of the body, it also removes the waste product of metabolic processes and maintains the body temperature of the bird (Lovette & Fitzpatrick, 2016).

Bird circulatory system

Birds, like mammals, have a four-cavity heart (two ventricles and two atria), where a complete process of separation of oxygenated blood from the blood carrying no oxygen is performed. The right ventricle pumps blood to the lungs, while the left ventricle must generate pressure to pump blood through the body (D'Elgin, 1998).

Birds tend to have larger hearts than mammals in proportion to the size of their bodies. The heart of the birds is of relatively large size, as it must cover the metabolic needs required to fly.

The Hummingbirds , Despite their small size, are the birds have a larger heart compared to the proportions of the rest of their body. This is because the constant flapping of its wings demands a high energy consumption.

Structure of the circulatory system


The heart is the most important organ of the circulatory system of any vertebrate animal. In the case of birds, it is divided into four cavities responsible for separating the oxygenated blood from the one that is not. The heart has the important task of distributing oxygen and nutrients to the body through the blood (Reilly & Carruth, 1987).

The heart of birds is similar to that of mammals, however, their structure is slightly different due to their lifestyle and needs. Birds have proportionally larger hearts than mammals, meaning that the average volume occupied by a mammal's heart is 0.4% of its body mass, while in birds it is 4%.

Smaller birds have especially large hearts compared to their size, as they require more energy to fly. On the other hand, the heart of the birds pumps more blood per minute than the heart of mammals.

The speed of heart beat is lower, but the volume of blood pumped is greater in birds than in mammals. However, the heart of the birds has a single aortic arch located on the right side of the body, while the mammalian heart has the same arch on the left side.

Veins and arteries

The blood located inside the body of birds flows through different types of blood vessels known as arteries, arterioles, capillaries and veins. Each of these channels performs different functions, as shown below.

  • Arteries: carry oxygenated blood from the heart to the body cells.
  • Arterioles: distribute the blood directly to the tissues and organs that most need it, through processes of vasoconstriction and vasodilation.
  • Capillaries: they perform an exchange between nutrients, gases and residual products between the blood and the cells of the body.
  • Veins: can be large or smaller (venules) and are responsible for driving the blood back to the heart so that it is again oxygenated and pumped back to the rest of the body.

Some of the most important arteries of the circulatory system of birds are the following:

  • Carotid: carries blood to the head and brain.
  • Brachial: Bring the blood to the wings.
  • Pectorals: carry the blood that goes directly to the pectoral muscles, necessary to fly.
  • Systemic arch: also called aorta, is responsible for bringing blood to all parts of the body, except the lungs.
  • Pulmonary arteries: carry blood to the lungs.
  • Celiac: are the most important branch that comes off the descending aorta. They carry the blood to the organs and tissues in the upper part of the abdomen.
  • Renal arteries: carry the blood that goes to the kidneys.
  • Femoral: carry the blood that goes to the legs and the caudal artery is responsible for irrigating the tail.
  • Mesenteric posterior: are responsible for bringing blood to the organs and tissues in the lower abdomen.

The blood distributed through the arteries around the body, flows back to the heart, directly into the first cavity or right atrium through the veins.

From the right atrium, blood without oxygen is displaced into the right ventricle, which pumps blood directly into the lungs to be oxygenated again (PoultryHub, 2017).

Oxygenation of blood

In the lungs, the blood is again oxygenated and travels to the left atrium of the heart, from which it is pumped to the left ventricle.

This last cavity through which the blood passes, is the strongest and most muscular of all, because it has the work of pumping the blood through the arteries that irrigate the whole body. Therefore, the left ventricle has a thick wall of muscle that allows it to fulfill this important task (Farner & King, 1972).

With each heartbeat, the process of oxygenation of the blood is repeated. Only mammals and birds have four cavities in their hearts that allow them to separate the oxygenated blood from the one that is no longer. In other animals, the heart has at most two cavities and the blood is mixed.

In order for the process of oxygenated blood to be more efficient, it is important that the oxygenated blood is constantly circulating through the body of the bird, and the blood without oxygen returns quickly to the heart to be oxygenated again.

An efficient process of blood distribution implies a more rapid metabolic process and more energy for the bird (Scanes, 2015).


  1. D'Elgin, T. (1998). The Circulatory System. In T. D'Elgin, The Everything Bird Book: From Identification to Bird Care, (P.18). Holbrook: Adams Media Corporation.
  2. Farner, D. S., & King, J. R. (1972). Avian Biology, Volume 2. New York - London: Academic Press.
  3. Lovette, I.J., & Fitzpatrick, J.W. (2016). Circulatory System. In I. J. Lovette, & J. W. Fitzpatrick, Handbook of Bird Biology (Pp. 199-200). Oxford: Wiley.
  4. (2017, February 1). Poultry Hub . Retrieved from Circulatory System:
  5. Reilly, E. M., & Carruth, G. (1987). Circulatory System. In E. M. Reilly, & G. Carruth, The bird watcher's diary (Page 30). Harper & Row.
  6. Scanes, C.G. (2015). The Cardiovascular System. In C. G. Scanes, Sturkie's Avian Physiology (Pp. 193-198). London: Elsevier.

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