Organs - Here's a simplistic breakdown of an avian's organs. Notice there isn't much here, just the basics. The noticable difference with a bird's set of organs, is the 'Gizzard', which is a completely different digestive system than say a land mammal's. Because birds have a weak jaw, and no teeth, they require an advanced digestive system to breakdown it's food. The crop is a temporary storage area for the avian's food, as the gizzard is a large muscle which breakdown it's food (basically a normal stomach). This reference would be great to use if you're drawing again, gory scenes or some sort of macabre which requires references of bird organs.