1. Inside the Bird
Internal Anatomy

2. Digestion
Food goes down esophagus to crop for storage (not all birds have crop)
Food passes to stomach and is broken down by chemicals
Then to the gizzard. Grit and small stones swallowed by the bird go in to the gizzard and grind the food to mush.
The mush goes into the small intestine where nutrients are absorbed.

3. Digestion
Undigested matter passes into th the large intestine and exits as waste along with undigested seeds that later sprout
Complete digestion of fruit takes only about 15 minutes.
Digestion of nuts takes several hours.
Birds are extremely athletic and generate a lot of heat. They require a lot of oxygen.

4. Respiration Air goes into the lungs
Oxygen then goes into the blood stream
Cools their blood
Lowers the temperature of the internal organs

5. Circulatory System - Heart
Birds have very efficient cardiovascular systems that permit them to meet the metabolic demands of flight (and running, swimming, or diving). The cardiovascular system not only delivers oxygen to body cells (and removes metabolic wastes) but also plays an important role in maintaining a bird's body temperature. The avian circulatory system consists of a heart plus vessels that transport:
nutrients
oxygen and carbon dioxide
waste products
hormones
heat
Birds, like mammals, have a 4-chambered heart (2 atria & 2 ventricles), with complete separation of oxygenated and de-oxygenated blood. The right ventricle pumps blood to the lungs, while the left ventricle pumps blood to the rest of the body. Because the left ventricle must generate greater pressure to pump blood throughout the body (in contrast to the right ventricle that pumps blood to the lungs), the walls of the left ventricle are much thicker & more muscular.

6. Instinct Governed almost entirely by instinct
Can outperform similarly sized land animals in tests
Crows and ravens recognized as smartest of all birds

7. Singing Birds us a syrinx to sing
Prefer to sing more on cloudy days and in the woods rather than open fields
Songs thought to
Attract mates
Establish territory
Ward off rivals
A robins territory is about ¼ acre or about two house lots

8. The strength of a bird's skeleton is more than adequate even though the bones are hollow
A hawfinch 7 inches long (18 cm) exerts about 151 lbs. (68.5 kg) pressure in order to crack open an olive seed.
The shoulder, hip and chest bones of birds are fused together - which improves the strength of the birds structure
Skeleton is lighter than in all other land-dwelling animals.
Large keel bone supports the muscles that power the birds wings
Bones