<|im_start|>system
You are a helpful AI assistant.<|im_end|>
<|im_start|>user
Do birds have periods?<|im_end|>
<|im_start|>assistant
No, birds do not have periods. Periods are a monthly shedding of the uterine lining in humans and other mammals. Birds do not have a uterus, so they cannot have periods. Instead, birds lay eggs. When a bird ovulates, an egg is released from her ovary and travels down her oviduct. The egg is then fertilized by a sperm cell and incubated in the oviduct until it hatches.

Some people may mistakenly think that birds have periods because they see blood around a bird's nest. However, this blood is not from a period. It is from the bird's cloaca, which is a common opening for both the reproductive and digestive systems. When a bird lays an egg, it can sometimes rupture the lining of the cloaca and cause bleeding. This is not a serious condition and usually heals on its own.<|im_end|>
<|im_start|>user
Thanks! But if the egg in a shell is unfertilized, how does a chicken develop? Or how does the egg get fertilized **in the shell**?<|im_end|>
<|im_start|>assistant
Chickens and other birds can lay eggs without being fertilised. These eggs are called unfertilised eggs. Unfertilised eggs cannot develop into chickens. Only fertilised eggs can develop into chickens.

Fertilised eggs are created when a sperm fertilises an egg. A rooster produces the sperm and a hen produces the egg. When a rooster and hen mate, the rooster's sperm fertilises the hen's egg. The fertilised egg then travels down the hen's oviduct and is laid in a shell.

Unfertilised eggs are laid when a hen ovulates but does not mate with a rooster. Ovulation is the process of releasing an egg from the ovary. Hens ovulate about once a day.

Unfertilised eggs are still nutritious and can be eaten. They are also used to make chicken products such as mayonnaise and egg nog.<|im_end|>