The fun and educational site for parrot loving kids of all ages!

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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External 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.....

Eye

ag anatomyBirds have some of the best eyesight in the animal kingdom. Vision is a parrot's most critical sense as it is important for its ability to survive. Parrots' ability to see with great accuracy at long distances, and in enhanced color, helps them to detect predators. It is typical for prey animals to have their eyes spaced widely on their heads, and this is the case for parrots. With their eyes placed on the side of their heads, they are better able to monitor movement from all angles, and they have close to a 360° view of their surroundings. A few other interesting facts about a parrot's eyesight are:

  • Birds have eyeballs that are relatively large in comparison to the size of their heads.
  • Parrots have two fovea per eye, which operate independently. These enable parrots to focus on more than one object at a time.
  • The lateral placement of their eyes results in a limited binocular field. This means that parrots have poor depth perception .
  • Birds have the ability to focus much faster than other animals.
  • A bird's eye isn't capable of much movement, therefore birds can often be seen moving their heads in order to get a better look at something.
  • Birds close their upper and lower eyelids only to sleep.
  • Birds have a transparent third eyelid for blinking that sweeps across the eye from the inside to lubricate and clean the cornea. The transparency of this eyelid helps birds to remain aware of their surroundings.
  • Night vision is poor in parrots making them more vulnerable to attack at night from owls and bats.
  • Compared to humans, parrots can distinguish more colors and see a wider range of colors due to their ability to distinguish UV light.
  • Parrots' eyes can be quite expressive! Their pupils often dilate when they are excited or fearful.

Ear

Birds have ear holes instead of ears! These ear holes are hidden by specialized feathers known as auricular feathers. Although parrots don't have external ear structures, they do have three inner ear chambers just like we do. A parrot's middle ear has only one bone versus the three bones (Hammer, Anvil and Stirrup) found in human ears.

The ability to hear is very important to a bird's existence in the wild, especially since birds often rely on communications between flock members to warn of predators. Here are a few facts about a bird's hearing:

  • Birds can hear a smaller range of sound than humans.
  • Birds are less sensitive to the high and low ends of the frequency range.
  • Birds can distinguish rapid fluctuations (changes) in pitch and intensity much better than humans can.
  • The replay speed of a bird's call would have to be slowed by a factor of 10 for us to be able to detect all of the details that a bird can hear.

Cere

The top part of a parrot's beak is called the cere. The cere is a soft, fleshy swelling where the bird's nares (nostrils) are located. The color of the cere varies from species to species. You can often tell the sex of a budgie by looking at their cere. The cere is blue for mature males and it is pale brown for females. When they are babies, both the male and female budgies have pinkish ceres!

Beak and Tongue

Birds have beaks instead of teeth. Parrots are also sometimes referred to as "hookbills" due to the curved, hook-like shape of their beaks. Finches and canaries with their short, straight beaks are considered "softbills."

25001068A parrot's beak is short and wide with a curved upper mandible that hooks around the lower mandible which has a sharp, upward pointing cutting edge. The upper mandible in a parrot has a level of mobility not common to other bird species with hooked bills (i.e., hawks). This extra flexibility, in combination with the lower mandible's cutting edge, allows a parrot to easily crush hard seeds and nuts. Beaks are made out of keratin, just like our fingernails.

The shape of a bird's beak determines the type of diet it can consume (eat). A parrot's beak is very strong as demonstrated by their ability to crack open nut shells and devour fruits with thick skins. Parrots are extremely agile with their powerful beaks. They can use them to delicately groom their feathers and their mates' feathers as well! All in all, beaks are amazing tools!

Parrots have tongues that are strong and broad. Their tongues assist them with eating fruit, seeds, nectar, and pollen. Parrots that eat seeds use their tongues to manipulate seeds or position nuts in the beak. A parrot's tongue is different from a human tongue because it has a bone through the entire length of it!

Skin

A bird's skin has sensory nerve endings that detect temperature, pressure and pain. The skin of a bird is covered by feathers with the exception of its legs, feet, cere, and eye patches. There are no sweat glands in birds. In order to stay cool birds rely on evaporative cooling through respiration. Up to three-quarters of the air a bird breathes is used for this purpose.

Wings

wing-feathersThe bone structure in a bird's wing is very similar to the arm and the hand of a human. Wings are constructed from several types of feathers. The primary feathers are the ones connected to the skin over the "hand" bones, while the secondaries are connected to the skin surrounding the "forearm" bones. Both sets of feathers also have a layer of coverts on top of them, followed by another layer of marginal coverts. On the inside of the wing, there are the scapular feathers, sometimes also called the tertiaries.

Feathers

Feathers are unique to birds and they are elegant masterpieces of design. Feathers are made out of keratin, just like our hair and fingernails. Parrots have between 2000 to 3000 feathers! The three most prevalent categories of feathers, each of which serves a distinct purpose, are:

  1. the flight feathers, which are located on the wing and tail are long, strong and flexible to provide power for flight;
  2. the contour or body feathers which provide for a bird's smooth shape and color. The contour feathers overlap each other like roof shingles to protect the skin from injury, the weather (wind and rain) and sunlight; and
  3. the down feathers, which are soft and fluffy, and help to insulate birds by trapping air and preventing their skin from getting wet.

Feathers also serve:

  • to assist some species to blend into the environment (camouflage);
  • to show off secondary sex characteristics, and
  • to allow for courtship display (tail-fanning).

You can sometimes tell if a bird is healthy or sick just by looking at its feathers. A healthy bird will have shiny, brightly colored and smooth plumage (feathers). By contrast, an ill, stressed or malnourished bird's feathers often have stress bars, or they are dull, discolored and rough in appearance. Poor feather condition, in many cases, is simply the result of poor diet, hygiene and the lack of bathing opportunities.

Tail

A bird's tail consists of a tailbone, a set of flight feathers, and a layer of covering feathers at the base of the tail. The tailbone is a group of six fused vertebrae called the pygostyle, which supports the tail feathers. Tail feathers are arranged in overlapping pairs. Beginning with the outer pair of tail feathers, each succeeding pair of tail feathers overlaps on top of the other. Rump muscles control both the pygostyle and the tail feathers. Some species of birds can open their tails like fans and often do so when they are excited.

A bird's tail is important to a bird's ability to fly because

  • it provides lift for a major portion of the bird's body because the wings are positioned slightly forward of the bird's center of gravity, and
  • it acts as a rudder to help steer the direction of a bird's flight, and it also helps the bird land, take off, and change altitude.

Bird tails also provide balance when they are perched.

Feet

Birds spend almost 24/7 on their feet, even when they sleep. The only time they aren't using their feet is when they are flying.

One of the unique anatomical characteristics of a parrot is the arrangement of its toes. A parrot's foot has two toes pointing forward and two toes pointing backwards. This zygodactyl toe arrangement enables parrots to be proficient (very good) at climbing and grasping objects. Most birds have a three toe-forward, one toe-backward foot structure as illustrated below:

parrot foot versus chicken toes

Here's a few more fun facts:

  • Each toe in a parrot's foot has a different number of bones in it!
  • Do you know why doesn't a bird fall off of its perch when sleeping? Parrots have tendons in each leg that can lock the bird's feet to a branch. Their toes actually tighten around the perch as the bird lowers its body into a resting position and falls asleep. To unlock this tight grip, the bird needs only to stand up straight.
  • Have you ever heard of Herbst corpuscles? Herbst corpuscles are groups of nerve endings found in the toe pads of a parrot's foot. These nerve endings are very sensitive to vibrations and can serve as a warning device to alert a bird to possible predator movement in its environment.

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