Birds belong in a class all by themselves. This class is called “Aves”. Although there are over 8,600 species of birds, all of them, no matter what type, have certain basic characteristics and needs in common:
Birds have an extremely high metabolic rate. They must maintain a very high body temperature, which can be from 104 to 112 degrees. The average is 107 degrees.
Bird feathers derive from reptile scales, an evolutionary process. There are five different kinds of feathers.
Most bird bones are pneumatic meaning they have a pocket of air in the center of the bone where the marrow would be found in a dog. This makes bird bones much lighter than mammalian bones thus allowing for birds to be light enough to fly.
The respiratory system is complex in birds. There is no diaphragm so the movement of air is different from other animals. Birds have air sacs and lungs. The movement of air and the air sacs is very complicated and efficient
There are no teeth in birds. They have saliva that hydrates the crop contents. The upper, hard palate, forms a cleft or choana, which is the communication of the nose to the mouth. The crop is a sack like organ at the base of the throat. It is the storage site for ingested food.
Undigested food in the crop passes through two stomachs prior to reaching the intestine. The true glandular stomach is called the proventriculus where hydrochloric acid and digestive enzymes are secreted. Food then moves to the ventriculus, or gizzard, which is a heavily muscled organ that pulverizes or grinds the food. After it is pulverized, it goes into the small intestine where nutrients are absorbed. Birds have a common area into which their digestive tract, urinary tract and reproductive tract empty called the cloaca.
The kidneys excrete byproducts of metabolism, just as in humans. In birds the byproduct is uric acid, a solid substance. That is the white solid substance is visible in the droppings. There is also a clear liquid component of the urine.
The blood supply to the legs and intestines is common to the blood supply with the kidneys. Therefore, infections in the feet or intestinal tract can cause kidney disease. If a bird has a sore foot, it needs immediate attention because the blood supply goes directly to the kidney and can cause infection to rapidly spread there
The reproductive system of birds is of interest. Birds have only the left ovary and oviduct that fully develop. In the female, the right ovary and oviduct atrophies. In the male, both right and left sides develop into testicles. Birds can lay eggs without ever being exposed to a male bird. These eggs are unfertilized, therefore, they won’t hatch.
In birds, the nerves that supply the legs travel from the spinal cord through the kidney tissue to the leg. Any disease of the testicle, ovary or kidney can present as lameness.
How to Identify a Healthy Bird
Eyes should be clear, without crustiness. Plumage should be glossy, brilliant, and iridescent. The bird should stand high on its perch rather than rest on its hocks.
Make sure there is no “pasty vent” which mean there is no feces stuck in the feathers around the cloaca or vent region. Make sure the breast muscle is full and round so that the breastbone is not prominent. A bird with a breast shaped like the pointed roof of a house is too thin. Does the bird have all its toes? Are there any defects in the way it holds its body? A weak bird will “tail bob” meaning it will sit on the perch and its tail will bob up and down. That means either it is having problems keeping its balance or it is having difficulty breathing. Birds with abdominal disease i.e. egg binding, tumor or fluid in the abdomen will often present with a obvious “tail bob”.