Unlike mammals, pigeons do not have visible reproductive organs, but it's possible to guess their genders based on behavior and differences in their appearance. To be absolutely sure, submit a feather sample for genetic testing.
It's a Male
You can't tell male pigeons from female based on color. It is possible to visually determine the sex of pigeons based on appearance and behavior, but these indicators are educated guesses at best. The bodies of male pigeons are more robust; males have thicker necks and wider heads. Males tend to carry their tails lower and will fan them out when strutting to impress a female.
Male pigeons woo females by pursuing them and strutting to impress them. They may turn in circles or from side to side while cooing loudly and bobbing their heads up and down. Males keep watch over their mates to ensure that no other males woo them. Male pigeons may drive females to a nest or away from other pigeons by pursuing and pecking.
It's a Female
Mature female pigeons, with their typically more slender bodies and narrower heads than males, tend to carry their tails level with their bodies or higher -- however, this does not apply to pigeon breeds such as fantails that are bred to carry their tails vertically. When frightened while in the company of their mates, female pigeons may attempt to hide beneath their mates.
Females pigeons will solicit their mates for feeding by pecking around the male's beak. This behavior resembles kissing; it usually occurs just before a pair of pigeons mates. The female accepts feeding by the male, then crouches low to accommodate mating. Female pigeons are less vocal than males, but will coo to greet their mates or grunt as a warning to those approaching their nests.
Pigeons mate for life; they share the care of their eggs and young. A female pigeon usually sits on her eggs from late afternoon until mid-morning. When the male returns to the nest, he'll meet the coos and struts. He sits on the nest from mid-morning until late afternoon.
Both males and females feed their young a regurgitated mixture of food. Both male and female pigeons will defend their nests by pecking, slapping intruders with their wings and making growling or grunting noises.
Observing Group and Pair Behaviors
Observing how pigeons act within a pair or group of three or more more may help determine gender. With two males and a female, you may see the males woo the female by strutting and cooing; the two males may also squabble.
Female pigeons are typically docile; they aren't aggressive with other pigeons unless crowded or protecting their nest and young. If two females and a male are caged together, the male may attempt to woo and mate with both females, or he might select one of the females as his mate and the single female bird may be ignored or attacked by the mated pair.
A group of females would likely show less aggression toward one another and may lay unfertilized eggs. This only proves that one of more birds within a group is female -- unless you observe the laying of eggs, you can't be sure which pigeon laid them.
Two pigeons of the same gender confined together may assume male and female roles, with one bird assuming its own gender role and the other assuming the role of the opposite sex. When this occurs with two males, you'll never find eggs.
The number of eggs laid within a pair or group isn't always an accurate indicator of gender. Pigeons usually lay two eggs per clutch, but some females will lay one egg; on occasion a pigeon may lay three. Sick or stressed females may not lay any eggs even when paired with a male.
Methods for Determining Gender
Pigeon keepers may use a method of sexing pigeons called finger sexing, which requires placing a finger between the vent bones. The space between vent bones on a male pigeon is typically narrower than on a female, whose are spaced wider to accommodate egg laying. Due to variances in anatomy and breed structure, this method is inaccurate and is not recommended unless performed by an avian veterinarian.
DNA testing is the only 100 percent accurate method of sexing pigeons unless you observe a female laying an egg. DNA testing determines gender by analyzing a sample of a specimen's blood or feathers. Testing a small feather sample is safer and has gained favor over blood sample testing.