Pigeons are some of the most visible birds on earth. They are often seen wandering cities with their stubby necks reaching out for food. Some pigeons, like the feral rock pigeon, weigh only a pound or two. Other pigeons, such as the crowned pigeons in New Guinea, can reach almost 10 pounds. Both male and female pigeons have sex organs that play a role in reproduction.

A female pigeon will often choose a male that has the same markings as her parents, although this theory is contested by one that proposes she will find a rare looking male. Males display themselves by puffing and strutting around the female pigeon. The female picks the male pigeon she wants as a mate by putting her beak inside the male's beak.

The female moves her tail to the side and the male gets behind her. Both pigeons have small protrusions known as "cocacal protuberances." The pigeons touch each other's protrusions and insemination occurs quickly. The male pigeon ejaculates within a half second after mounting and touching the female pigeon, and his sperm enters her reproductive tract.

Most male birds, including pigeons, have no external sex organs. The male pigeon has two interior testes that swell during the breeding season and produce sperm. Adult female pigeons have only one ovary, although two are present in their embryonic stage. The ovary contains all the egg cells that the female will need to reproduce in her lifetime. These ovaries are connected to an oviduct, which swells with the presence of a fertilized egg. The female reproductive tract is a complex canal that includes a funnel that holds the ovulated egg. The male's sperm fertilizes the egg in the funnel of the oviduct.

The egg travels through the female reproductive track, gaining substance and nutrients and the shell is formed. The egg is then stored in the female's uterus until it is laid. Two eggs are often produced and laid within twenty-four hours of one another.