How does a chicken know to sit on her fertilized egg and not just lay the leave coop?

Chickens don't "know" in the human sense. Their behavior is driven by a combination of instinct and hormones.

Here's how it works:

Instinct: Chickens have an innate instinct to brood, meaning to sit on a nest of eggs. This behavior is essential for the survival of their species.

Hormones: After laying eggs, a chicken's body produces hormones that trigger a change in her behavior. These hormones make her more likely to:

* Stay in the nest: She'll become less active and more inclined to stay put.

* Be protective: She'll become more aggressive towards anything that approaches her nest, especially if she senses a threat to her eggs.

The process is more about a biological urge than conscious thought:

* Hormones: The hormones responsible for brooding are produced by the chicken's ovaries.

* Nesting instinct: The nesting instinct is triggered by the presence of eggs in the nest.

Essentially, the chicken's body is programmed to sit on her eggs, and her hormones make her more likely to follow through on this instinct.

Important note: Not all chickens will brood. Some breeds are more prone to brooding than others, and some individual chickens simply might not be as inclined to sit on eggs.