Actually, unlike mammals, birds do not have a penis. This is a fact that seems to both surprise and fascinate many people.

Birds have a single opening used for three purposes: mating, getting rid of urine, and getting rid of feces. This opening is called the "cloaca" and it is located on the posterior end of the bird beneath the tail. Sometimes the cloaca is also referred to as the "vent." During the mating season, the cloaca becomes engorged and you will notice around the same time birds start showing more lovey dovey behavior toward the opposite sex.

When birds mate, the perform what is called a "cloacal kiss." The female stands rather stiffly and the male stands on the back of the female. He first balances himself, which can be quite a feat in some bird species, and then moves his cloaca over the female's cloaca where he deposits his sperm. Some male birds are very vocal during this process that calls attention to the act. It is actually a fascinating thing to watch.

Fertilization is not always instant in birds. The female bird is capable of storing sperm for a rather long time.

There are exceptions to this style of mating in the bird group. These exceptions include certain types of ducks, raptors, and ostriches where the male has developed a "tubular" structure for delivering the sperm but it could hardly be called a penis.

Some scientists believe that this pseudo-penis developed in ducks because the drakes (male ducks) have so much competition to father a duckling and a "penis" may give an advantage where copulation is taking place in the water.