Most birds mate by contact at the cloaca area.
Sperm transfer from the male occurs when each partner's cloaca everts and tiny papilae protruding from the posterior walls of the male's sperm sacs in his cloaca are brought into contact with the opening of the female's oviduct. A few birds have an erectile, penis-like organ but not all birds. This intromittent organ is a special modification of the ventral wall of the cloaca and it exits in birds such as tinamous, most waterfowl, currasows and ostriches. Chicken and turkeys have a small penis, which enlarges with lymph fluid that is added to semen in the vas deferens in the reproduction system. Ejaculation of this fluid occurs through a longitudinal phallic groove.