Final answer:
The uterus is the site of plumping and shell formation in the avian oviduct, while fertilization typically occurs in the fallopian tube in humans.
Step-by-step explanation:
In the avian oviduct, the structure responsible for the plumping and shell formation of eggs is the uterus. This is where the egg receives most of its size and mass through the addition of albumen (egg white) and later gets enclosed in a calcified shell, readying it for laying. As for the human female reproductive anatomy, fertilization usually occurs in the fallopian tube, also known as the oviduct. It is here that the sperm meets the egg, resulting in fertilization. The ovary is the site where the egg develops within a follicle and is released during ovulation. After fertilization, the developing embryo travels to the uterus, where implantation and further development occur.