Skeletal System
The avian skeleton is very unique, having been adapted for flight in most species. It is lightweight and delicate yet very strong. Most of the long bones are hollow to make them lighter. The inside is reinforced with a honeycombed substructure. The main thing you need to know about is the sternum. Flying species have a pronounced keel, the place on the sternum that the flight muscles attach to. Birds that are clipped too severely can crash land and easily injure their keel. See the Respiratory System below for more information on the sternum and its function.

Respiratory System
The avian respiratory system differs from mammals in many ways. Bird respiration is much more efficient. Birds do not have a diaphram. In mammals, this muscle moves up and down to expand and contract the chest cavity. This is what causes the lungs to expand and air to rush in or out. Birds push the sternum in and out to the same effect. Owners therefore must be careful when holding their birds about the waist. If held too tightly the sternum will not be able to expand and the bird will suffocate.

The flow of air enters through the nostrils, down the trachea and into the lungs and air sacs. The trachea, or windpipe, is what breeders have to be careful of while handfeeding. Syringes should be aimed from the bird’s left to right (over the trachea and into the esophagus) to avoid aspirating the chick. Bird lungs are very compact and take up much less space than mammal lungs. With the help of thin-walled air sacs which extend through the body cavity and even into the bones, birds can keep a continuous flow of air through the lungs. If your bird ever starts to inflate like a little balloon, they may have punctured an air sac.

Breathing rate varies depending on size of birds. A hummingbird breathes 143 times per minute while a turkey breathes 7 times per minute. This rate increases during flight. 

Click here to learn more about avian respiration.

Digestive System

Birds do not chew their food and have specialized digestive tracts to compensate. All food must be broken down within the body itself. First the food travels down through the esophagus and into the crop. The crop is actually just an expanded section of the esophagus and it acts as a holding tank for food before it can enter the proventriculus- the bird version of a stomach. The proventriculus produces acid and adds enzymes which aid in breaking down the food, which is next passed to the gizzard. The gizzard helps grind tougher food like seed. According to Ornithology by Gill, a turkey gizzard can “pulverize English walnuts, steel needles, and surgical lancets.” The gizzard is highly keratinized to make the surface rough (keritan is what makes up fingernails and hair).

Food then takes its time passing through the intestinal tract, where nutrients are absorbed. Birds that eat large quantities of plant matter (greens, not fruit) will have a large cecum. This area of the intestines specializes in breaking down plants via acid, enzymes, and specialized bacteria. Parrots do not have enlarged cecums. Waste is then expelled through the cloaca, or vent.

Reproductive System

The reproductive organs shrink when birds are not in mating season. This drastically decreases their weight, making flight easier. Males have two testes and females have one ovary.

Eggs are produced thus: The ovum is fertilized and passes through a long tube called the oviduct. Each section of the oviduct adds a different part to the egg, just like an assembly line. In the infundibulum the egg stays 20 minutes before passing along to the magnum, where the albumen (egg white) is added. Now the egg goes to the isthmus, where inner and outer membranes are formed around the albumen. This takes about an hour. In the uterus the shell and all pigments are added. This process takes the longest, about 20 hours. The egg then passes through the vagina and out the cloaca.

Ever find a little pink or brown thing inside a chicken egg? Laying hens do not have access to roosters, so their eggs are not fertilized. If you find something odd in an egg it is most likely a piece of the reproductive tract that sloughed off while the egg was passing through.

Body Parts
Ever wondered what names like green-cheeked conure, golden-mantled rosella, red-lored amazon and red-rumped parakeet are referring to?

1. Crest
2. Nape
3. Mantle
4. Upper back
5. Lower back
6. Tertials
7. Primaries (clipped)
8. Breast
9. Foreneck
10. Cheek
11. Lores
12. Crown
13. Forehead
14. Cere
15. Chin
16. Throat
17. Metal band
18. Rump

Copyright © 2011 by Karen Trinkaus. May not be reprinted or used in any way without the author’s permission. Images taken from Parrots of the World by Forshaw where noted.