Baby chicks are similar in appearance, regardless of whether they are male or female. Chicks do not typically develop secondary sexual characteristics until several weeks after they are born. However, it is possible to search for subtle differences between cockerels, or young roosters, and pullets, or young hens, to identify their sex.
Male Genital Organ
Cockerels possess a larger sex organ than pullets and it can be seen almost immediately. "Vent sexing" a baby chick is one way of looking for the presence of a genital organ on a chick. Cockerels have a small pimple-like bump inside their vent, located underneath its tail. Pullets may also have a pimple-like bump, but they are almost always smaller in size. Vent sexing is performed by lightly squeezing a chick and looking inside its vent for the presence of a male sex organ.
Combs and Feathers
Cockerel combs, which is the growth on top of their heads, turn pink and darken at an earlier age than pullet combs. Noticeable differences between pullet and cockerel combs can be seen in as little as three weeks. Conversely, a pullet's feathers typically develop faster and more evenly than cockerels, whose feathers tend to grow in patches. Feathers growing near the neck and back are oval and rounded in pullets, but are pointed and shiny on cockerels.
Tail, Legs and Head
Differences in development of the tail, legs and head are observable within a couple weeks. Pullets' tails tend to develop more quickly and are long and straight. A cockerel's tail grows slower and tends to be stumpy and curved. Pullets' legs remain short and delicate, whereas a cockerel's legs will lengthen and appear sturdy after a few weeks. Similarly, a cockerel's head is larger and more angular, whereas a pullet's head is small and round.
Posture and Behavior
A cockerel tends to stand more upright and erect than a pullet, which remain lower-set in its stance. A cockerel is also more prone to behaving noisily and aggressive as its develops. This includes an increased level of alertness and attempts to crow before reaching adulthood. Pullets are usually more docile, but can also emit aggressive and noisy behaviour.