What type of hens alert the flock of danger

[ChickenPerson999999]

What hens alert the flock of danger, I know that some breeds of hens alert the other hens of danger. I can’t get a rooster because I already have one and I don’t want to have two of them. In case a hawk comes I’d like it not to be just a rooster making alert calls because I will want something else to help the rooster out a little. I can’t just have a bunch of ordinary hens and a rooster protecting them all by himself. So what types of hens do you think will help protect or warn my flock of danger?

 

[Trimurtisan]

I can’t just have a bunch of ordinary hens and a rooster protecting them all by himself.

In general, any hen that can see above them is likely of caling out alerts (none crested breeds).
When something flies over here there's about 50 chickens/ducks that start making noise, males and females. Ironically my best alert caller was a bantam Silkie rooster. He was constantly watching the sky.

 

[Folly's place]

Chickens raised without adults present will still alert to danger, but it can take a bad predator experience or two for the survivors to really be aware and more watchful. In a flock including older birds who have seen predator attacks, there's more alertness.
Some breeds are more careful too, and some individuals.
Mary