Raising poultry such as chickens can be both emotionally and financially rewarding for commercial farmers and amateur pet owners alike. One of the first elements to consider when you decide to keep chickens is gender. In some places, sexually mature roosters are prohibited, making this knowledge even more important. Aside from knowing that hens lay eggs and roosters crow, you also can tell the sex of the chicken by other means.
The easiest place to start is with the chicken's head. The comb and wattles are the fleshy, most times red parts on the chicken's forehead between the eyes and drooping down from the sides of the beak, respectively. On roosters, these are noticeably larger and more pronounced than on hens. This difference grows as the chicken does. The tail feathers of roosters are often larger and more pointed than those of hens as well.
There are several differences in behavior you can use to determine the sex of your chickens. Roosters will crow. This is a distinctive sound that hens cannot make. Roosters tend not to shy away when startled. In fact, roosters can be rather aggressive when cornered, though attempting to scare chickens to determine their sex is both dangerous and partially unreliable. Hens tend to frighten easily. Of course, hens are which lay and incubate the eggs.
In the 1930s, Japanese professor Kiyoshi Masui popularized a method of sexing day-old chicks by simple observation of the vent area -- the backside of the chick. Trained vent sexers can correctly identify the sex of hatchlings close to 100 percent of the time. The training results in an intuitive kind of knowledge-by-sight that is difficult to describe. If you have bred chickens for a long time, take a look at the backside of your chicks, but do not rely solely on this method unless you have been trained.
Certain crossbreeds of different varieties of chickens will yield differences in feather type and coloration from hatching that can be used to distinguish males from females. These genes are sex-linked -- that is, the same gene that determines sex in these breeds also determines plumage coloration. From a genetic standpoint, using these features to determine sex is 100 percent accurate from Day One, as long as the parent chickens are purebred. For examples and more information, see this page from the University of Kentucky.