How does a hen know if an egg is fertilized?

[RW1984]

Say I want to let nature work and have some hens hatch their eggs.
How will they know if they can be hatched or not? I have roosters. I’m just not sure if a hen that goes broody will know if that particular egg is fertilized it just a dud?

 

[Oncoming Storm]

I don’t think they do. I’ve heard of hens going broody and sitting on eggs when there is no rooster in the flock at all.

 

[Chookwagn]

sometimes a broody wil kick out an egg or two halfway thru incubation and 90% of the time the eggs they kick out are duds.... somehow they know.

 

[black_cat]

They don't always know from the start...I've heard of hens trying to hatch golf balls.

 

[black_cat]

You can also buy some fertile eggs of a specific breed for hatching.

 

[MarkJr]

My broody would try and incubate tennis shoes if that’s the only thing available to lay on.

 

[50-45-1]

I have a hen right now trying to hatch a clutch of golf balls and a rock.

 

[MarkJr]

Look something like this???

 

[RW1984]

Well they aren’t laying eggs yet but they will be soon. I was just curious. Trying to learn before hand.
Haha thank you everyone for your insight too! Seems these birds will try and hatch anything they can squat on

 

[AllenK RGV]

My silkies will brood rocks or oyster shells so there is no innate fertility knowledge in my opinion.