Let’s talk about how baby chicks are made. Chickens reproduce sexually, meaning that they need a male and a female who combine their genetic material to create a genetically unique individual. Male chickens are called roosters or cocks, while female chickens are called hens.
But wait! Don’t hens lay eggs even without roosters?
Yes, they do. Let’s have a look at the female reproductive system.
A hen has one working ovary and a 2 feet long oviduct. Although female embryos start with two ovaries, usually only the left ovary develops fully. The right side stays underdeveloped, likely to avoid the strain of producing two eggs at once.
Here is a nice animation video of the 24-hour formation of an egg in a hen.
Without a rooster, the egg won’t be fertilized and no embryo will develop.
Like almost all the male birds, a rooster has no penis. Instead, he has two tiny nipples, or papillae, that serve as mating organs. They are located in the rooster’s cloaca. He deposits sperm into a hen by pressing his cloaca against hers in a process called the cloacal kiss. For this to happen, the hen crouches down, and the rooster balances on her back. When it's the right moment, she lifts her tail to one side, and he tilts his tail down for the mating. During this balancing act, the rooster's claws can rub against the hen's back, sides, and wings, in what's called treading.
The hen temporarily stores the sperm and releases it prior to the next ovulation. The sperm has about 5 hours to make its way up the oviduct to fertilize the next developing ovum.
Once a fertilized egg is laid, the embryo doesn’t start developing until it’s incubated with the proper temperature and humidity. A hen will lay a clutch of eggs (usually 5 to 12 eggs), one egg per day. Once she has a clutch, she begins incubating the eggs by sitting on them full time, leaving only for food and water. This allows all embryos to develop and hatch simultaneously, which is quite convenient for the mother hen so she doesn’t have to care and run after her first hatched chick while still having to incubate the others.
It takes 21 days for a chick to hatch. Here is a fascinating animation video of the chick development in the egg.
With two clutches a year, that’s a lot of hatchlings and half of them will turn out to be males! How to prevent chickens from breeding?
The only way to avoid having baby chicks when roosters and hens are living together is to remove the eggs daily. Be diligent and search all the nooks in the chicken yard as mother hens can be really good at hiding their clutch. There is no birth control nor spay/neuter surgery for chickens. Just pick up the eggs.
Note that we don’t condone the breeding of chickens. There are too many chickens looking for good homes. Contact your local shelter or sanctuary and adopt.