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disturbed or removed, and will rarely leave the nest to eat, drink, or dust bathe. While broody, the hen keeps the eggs at a constant temperature and humidity, as well as turning the eggs regularly. At the end of the incubation period, which is an average of 21 days, the eggs (if fertilized) will hatch, and the broody hen will take care of her young. Since individual eggs do not all hatch at exactly the same time, the hen will usually stay on the nest for about two days after the first egg hatches. During this time, the newly-hatched chicks live off the egg yolk they absorb just before hatching. The hen can hear the chicks peeping inside the eggs, and will gently cluck to encourage them to break out of their shells. If the eggs are not fertilized and do not hatch, the hen will eventually grow tired of being broody and leave the nest. Reproduction Chickens reproduce in a manner similar to some other animals. The female produces an egg which if fertilized can result in a baby chick. The true egg, the part that develops into the embryo, is located on the egg yolk. The yolk begins to develop in the ovary and after 10-12 days of development, ovulation occurs. If the female has been mating with a male, sperm will be present and fertilization can occur. The male chicken does not have a penis and therefore there is no penetration of the female reproductive tract at the time of mating. Instead the female inverts the cloaca (site of the common junction of the reproductive and digestive systems), which comes in contact with the male's inverted cloaca and receives the sperm. The cloaca is then drawn back into the hen's body and the sperm are captured. They then begin the journey up the length of the reproductive system. The sperm live inside the female reproductive system and each time an ovulation occurs (every 24-26 hours in good egg producers) the egg can become fertile. This process continues and matings at 7-10 day intervals are necessary to maintain fertility. After fertilization occurs the egg albumen, shell membranes, and shell are added to complete the egg formation process. The chicken usually lays the egg about 24 hours after ovulation.