|Let's Celebrate Pet Birds!|
T.J. Lafeber D.V.M.
12 FACTS AND CARE: DIGESTIVE SYSTEM
A Super Efficient System
The design and function of the digestive system is based upon the bird's extraordinary need for nutrition and energy. The gastrointestinal tract is faced with the problem of transforming ingested food into a utilizable form of nourishment and energy for billions of cells. To visualize the size of the task, consider this example: a small bird may eat 25% of his weight in food daily. With a 20 gram canary (two-thirds of a ounce), that would be 5 grams of food. Not much volume in the palm of our hand, but compared proportionately to man, a 150 pound person would be eating 37 pounds of food. The question arises immediately of how a bird is capable of handling this volume of food? And further, how could the digestive system begin to convert this bulk to a utilizable form fast enough to provide for the energy demands?
Refinement of the digestive system specifically for the purpose of processing proportionately large volumes of food is seen in the production line design of the gastrointestinal tract. The bird has two stomachs. The first one adds digestive juices to the food as it passes through on its way to the second stomach, which rapidly grinds the food into fine particles and sends it on to the small intestine,
By having a crop as the reservoir for food, it can deliver small amounts of ingest continually to the stomach, where it can be rapidly processed. This makes for efficiency, as it enables a relatively constant process of digestion to take place. If the bird had teeth to perform these grinding processes instead of the gizzard, the bird would spend a long time chewing its food, which would expose it to dangers that are avoided by its bolting the food down and flying to safety. Also, it is much more efficient to have the gizzard grind food for hours in a continuous action, as the quantity of food in proportion to the size of the animal is relatively great.
As food leaves the gizzard and passes into the intestines, it is mixed with digestive juices from the liver, pancreas, and the wall of the intestine. Bile from the liver acts to neutralize the acid from the stomach and to emulsify fats in preparation for further digestion. The pancreatic juices digest proteins, fats and carbohydrates, Once the food is digested, it is absorbed by the lining of the intestine, passed on into the blood stream, and distributed through the body.
The whole process must be synchronized and efficient, as the muscular activity of the intestinal tract propels the food through the intestine rapidly. A starling will have food pass through its digestive tract in twenty minutes, and in a parakeet, it takes less than two hours. The relatively small amount of feces in the droppings indicates the thoroughness of the whole digestive process.
The digestive system is functioning under this intensity because the bird has extraordinary demands for energy. Food, the fuel for the body, is burned at a much higher rate than for any other living thing. That this is true can easily be checked by noticing that the body temperature of pet birds ranges anywhere from 1040 to 1090.
Because energy is used rapidly, a bird must constantly depend upon food as a source of fuel. Fat reserves cannot be converted rapidly enough to energy to be of any importance. Any disturbance of the gastrointestinal tract which interferes with food digestion or absorption can cause the bird to starve to death in a few days.
The alimentary canal has many adaptations and unusual features compared to mammals. One of these, the cloaca, evolved to eliminate the need for a urinary bladder and colon. An exchange of an organ to replace two is good efficiency. To lighten the load-as needed in flight-the cloaca collects only a small volume and then empties, thus accounting for the many droppings which a bird has.
Since the cloaca has an influence on the arrangement and size of the droppings, knowing its structure makes interpretation of droppings easier. The feces enter from the large intestine on the bottom; the urine enters from the ureters (tubes leading from the kidneys) at the top. When the droppings are passed, the feces fall first, with the urine (white urates and fluid urine) coming second. In many cases, this allows the urine to cover the feces. A fold from the top of the cloaca separates the terminal part of the large intestine from the area where the urine is deposited. With this arrangement, at times urine is passed as a dropping without fecal material.
The oviduct (passage for eggs) enters the cloaca in the region of the ureters. When the female bird enters her reproductive cycle, the cloaca must enlarge to accept and pass the egg. The enlarged cloaca allows more material to collect, and thus, at this time the droppings become several times their regular size.
The capacity of the cloaca may vary from one bird to another of the same species. A 30 gram budgerigar may have 40-70 droppings daily, depending upon the cloaca size.