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Internal Anatomy

Birds are fascinating creatures. Who wouldn't want to just sprout wings and take flight like a bird? It's a captivating thought, at the very least. Birds have a highly developed anatomy that serves to enable the miracle of flight. To fly, they must be incredibly lightweight and yet extremely strong. The combination of these two seemingly opposing traits are reflected throughout the anatomical construction of a bird.

Adaptations for flight not only include the obvious anatomical features (wings and feathers) but they also are reflected in a bird's skeletal, digestive, respiratory and, cardiovascular systems. Let's take a tour through the major external and internal features of a parrot's anatomy.....

lungs pfzRespiratory System

A bird's respiratory system is responsible for putting oxygen into the bloodstream. Due to their high metabolic rate required for flight, birds have a high oxygen demand. Development of an efficient respiratory system enabled the evolution of flight in birds. Birds ventilate their lungs by means of air sacs. Air sacs can make up to one-fifth of a bird's body volume!

Birds breathe through their nostrils (nares) which are located at the top of the upper beak in an area called the cere. From their nares the air travels into a series of nasal cavities where the air is purified of dust and particulate matter. From the nasal cavities, air then passes through the trachea to the syrinx where the air stream is divided in two. Instead of going directly to the lungs, the air travels first into air sacs. It takes two inspiration/expiration cycles for the air to travel completely through the air sacs and the lungs.

Birds do not have a diaphragm. The entire body cavity acts as a bellows to move air through the lungs. The active phase of respiration in birds is exhalation, requiring muscular contraction.

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 and are often more toxic (harmful) to birds than to other animals.

Nervous System

A bird's nervous system is very similar to that of the rest of the vertebrates. The nervous system consists of the brain, the spinal cord, and nerves that run throughout the body. The primary functions of the avian (bird) nervous system are:

  • to coordinate the actions of the body by transmitting signals,
  • to provide sensory information about the internal and external environment, and
  • to store information as memory (brain).

Anatomically, a bird has a relatively large brain compared to its head size. Studies have shown that the brain-to-body size ratio of parrots and crows, the two most intelligent bird species, is actually comparable to that of higher primates.

Digestive System

digestion pfz A bird's digestive system has some unusual features that help to rapidly process its food. Birds have high energy needs and for this reason they need to digest food very efficiently.

The mouth of a bird is very different from ours, and they don't chew like we do. Birds don't have any teeth and their mouths don't have saliva. When birds eat, they use their beaks to open seeds, nuts and fruits. In the process, they break these items into smaller pieces.

Small pieces of food are passed through the esophagus into a holding area called the crop. While in the crop, the food is moistened and softened through the action of muscle layers. Parrots will regurgitate food that has been softened in the crop when they are feeding their young.

From the crop the food passes to the proventriculus which is where acid and enzymes start to digest the food. The next stop is the gizzard. In the gizzard the food is ground into a pulp by a group of muscles that contract and rotate the food against grit that is stored in the gizzard. When the food is sufficiently crushed it then passes into the bird's intestine.

Chemical digestion and nutrient absorption of the food take place in the small intestine. The small intestine receives bile from the liver and digestive enzymes from the pancreas that aid in this process.

The leftover materials then travel through the large intestine which consists of a short colon and a pair of caeca. Finally the bird's digestive tract ends in the cloaca where fecal and urinary material is collected before it is expelled through the vent

Urinary System

The urinary system is the body's waste removal system. The kidneys' main function is to process and remove wastes from the blood. Humans have bladders where urine is collected. Birds don't have a bladder, instead the waste extracted by the kidneys travels to the cloaca where they exit the body along with solid waste materials.

A bird's high body temperature and level of activity means that they need to conserve water. Because of this, their urinary system is designed to operate differently from humans. The urinary systems of most animals produce urea which needs to be dissolved in large amounts of water to be excreted from the body. Instead, birds produce uric acid that can be discharged as a thick paste along with the feces. This is the white chalky part of the bird droppings. A bird is able to urinate independently of defecating, or passing feces, but most of the time, the bird will pass urine, urates and feces at the same time. 

blood pfzCardiovascular System

The cardiovascular system is responsible for delivering oxygen to body cells and also plays an important role in maintaining a bird's body temperature. A parrot's circulatory system consists of a heart plus all of the vessels used to transport blood (arteries, veins, capillaries).

A bird's heart is a relatively large and powerful organ capable of very rapid contractions. It can beat up to 200 times per minute at rest and up to 800 times per minute while flying!

Just like mammals, a bird's heart has four chambers, two atria and two ventricles, which work like two separate pumps. After passing through the body, blood is pumped under high pressure to the lungs. Upon returning from the lungs, it is pumped under high pressure to the body. The high rate of oxygen-rich blood flow through the body enables birds to meet the high metabolic demands of flight.

Musculoskeletal System

768px-parrotskellydA bird's skeleton is highly adapted for flight. For example, birds have many bones that are hollow which makes their bodies more lightweight. The hollow bones are honeycombed with air spaces and strengthened by crisscrossing struts (supporting materials). This, combined with the fact that many of a bird's bones are fused and can't bend, make its skeletal system strong enough to withstand the stresses of taking off, flying, and landing.

Hollow bones not only lighten a bird's body weight but they also help to facilitate cooling. Respiratory air sacs often form air pockets within the semi-hollow bones of the bird's skeleton.
A bird's skull is extremely light in proportion to the rest of its body because birds don't have heavy jaws, jaw muscles, and teeth that are common to other animals.

In contrast to the rigidity of a bird's skeleton, the neck is extremely mobile. This allows a bird to see danger from any direction, as well as allow it to preen its own feathers. Flexibility is increased by the large number of neck vertebrae. A parrot has ten neck vertebrae compared to a human's seven. Because of this, a parrot can turn its head almost 180 degrees!

Most birds have approximately 175 different muscles, mainly controlling the wings, skin, and legs. The largest muscles in birds are the breast muscles, which control the wings and make up about 15 - 25% of a flighted bird's body weight.

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