reproductive tract of a female bird, extending from the ovary to the cloaca just above the vent; the walls of the oviduct are lined with muscles that move an egg through from the infundibulum at the top to the cloaca; the oviduct has several sections with discrete functions: the infundibulum which receives an ovum from the ovary and fertilized by sperm (unless there are no viable sperm available); the magum where the egg is surrounded by albumen; the isthmus where the shell membranes are wrapped around the egg; the uterus (or shell gland) where the hard calcium carbonate shell is formed; and the vagina from which the egg is pushed into the cloaca just prior to laying; most birds, including Bald Eagles, have only the left oviduct (and ovary), the right being absent or vestigial