While the rooster will mate with his hens throughout the year, she typically only incubates eggs when conditions are optimal. A hen choosing to incubate eggs is said to have "gone broody. Roosters have reproductive organs not unlike mammals, with testes that produce sperm. The sperm travel down tubes called vas deferens to sperm sacs. During mating — an unceremonious affair that lasts less than 20 seconds — the sperm leave the male through an opening called a cloaca, and enter the female through an entrance to her reproductive tract, called the oviduct.
From there, the sperm make their journey through the reproductive organs of the female. In a trip that may take a week or more, they swim through the hen's shell gland, then a narrowing in her reproductive tract called the isthmus, followed by the magnum and the infundibulum. There, they await the arrival of eggs in the process of forming.
A hen's eggs begin as yolks in the ovary, and once released they pass into the infundibulum, a funnel-shaped organ where the sperm are waiting. There they are fertilized, and pass out of the chicken via the same route the sperm entered. It's pretty simple. In contrast, hens only have one functional ovary.
In fact, most birds have this lopsided anatomy probably because it's more. For most male birds, the right testes is also smaller than the left. This trend does not carry over into roosters, however, probably because chickens are land-dwelling birds. In some bird species, the smaller right testes can even compensate if God forbid the left one gets damaged.
Instead both partners procreate using an external orifice called a cloaca. When the cloacae are touched together, sperm is transferred into the female reproductive tract. Since no penetration is involved, the act is simply called a "cloacal kiss. Unlike humans and most mammals, a female chicken has but one rear orifice with three functions. It is where feces and eggs exit her body and sperm enter.
One is to pass feces. The other is to transfer sperm to a hen. She stores sperm in her body and her eggs will be fertile for at least a couple of weeks and sometimes much longer before she needs to re-mate. Mammals produce liquid urine which leaves the body through the urethra. Urine contains urea. Instead they coat their feces with uric acid that exits their body through the cloaca as moist chicken poop. The rooster fans his wings flamboyantly while dancing around her in the same way a matador fans his cape to attract the bull.
I made that name up, but this move is commonly referred to as: the wing drag, wing drop or wing flicking. The Two-step In conjunction with the wing drag, a rooster will often dance in a circle, trying to position himself behind her to assume the mating position. Tidbitting Picking up actual or pretend morsels of food while calling the hen over to investigate is the oldest trick in the book. With apologies to Hasbro and my daughters whose Play Doh I pirated for this illustration, I present you with a rudimentary model of the rooster reproductive system.
Parts are not to scale. It looks like a small bump and is not at all similar in form or function to a penis except to the extent that semen exits through it. The rooster gets into position, which resembles a piggy-back ride, standing on her back, holding her neck feathers with his beak and steadying himself with his feet.
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