No. Regular sized roosters can mate with Bantam hens, and Bantam roosters can mate with regular sized hens. The resulting offspring will be a small to medium sized chicken.
A term rooster is used for the male bird (the hen is a female bird) of certain species . There are chicken roosters and hens, pheasant roosters and hens, turkey roosters and hens etc. Ducks are drakes and hens. Geese are the "Goose and the Gander".
Roosters are able to mate anytime of the year, but it's the hens that have to be willing to accept them that counts. Hens begin to lay eggs when the photoperiod (that's how long the sun stays in the sky during a single 24 hour period) gets longer, i.e., spring time. Since the term between copulation and egg development is short, roosters are able to breed hens in the spring time to encourage fertilization of eggs, which give chicks.
Well, hens are girls and roosters are boys...that cover it?
It is likely that the roosters are aggressive, too rough with the hens, or that there are not hens in ratio to the amount of roosters.
Hens
For adult chickens, roosters are generally a bit bigger, and have longer, showier tail feathers. You can also tell by behavior. Roosters will tend to be more commanding, and will usually avoid other roosters if they have enough space and there are enough hens, or else fight with them if the space is too small or there are not enough hens. They can also often be observed jumping on hens' backs to mate.
The amount of roosters needed for breeding hens is about one rooster per ten hens
Hens.
Yes they will.
No.
Better to say 4 roosters is too many for 4 roosters. The 6 hens can wait a bit and soon there will be one rooster a-go-go, one in the hereafter, one running away, and one squating on the ground. The hens could deal with 6 roosters, but the big boy a go-go won't stand for more than him with his flock. actually 1 rooster needs 5 hens to be satisfied other wise roosters will fight One rooster will service (fertilize the eggs of) up to 6 hens. If you have more than 6 hens, you will need another rooster. 4 roosters on 6 hens is not good. The roosters will fight and the hens will be exhausted running from all the roosters.