Male birds have two functional bean-shaped testes located within the body, just above the kidneys. The testes grow in size as the bird reaches sexual maturity. In seasonal breeders, the testes enlarge during the breeding. Sperm cells are formed in the tubules. Sperm production occurs more rapidly in birds as compared to mammals.
The testes also produce an important hormone testosterone That is very important in the development of secondary sexual characteristics such as courtship behavior, aggression and, in chickens, the waddles.
Once the sperm leave the testes, they travel through a small tube, known as the epididymis.
Sperm then enter the ductus deferens (a long narrow tube) and enters the cloaca. The ductus is densely packed with sperm during the breeding season. It takes from one to four days for the sperm to travel from the testes to the end of the ductus. Sperm undergo maturation in the male reproductive tract.
Depending on the breed, the main storage place for the sperm is the ductus deferens or the "seminal glomus."
The acrosome contains an enzyme which enables the sperm to penetrate the egg.
Most birds mate by joining their “cloacas” with the male sperm going into the female's cloaca.