I have about 30 guineas. This is an age related thing for the most part. They reach that six month to about 8 month period and can be very vicious towards other birds. My flock of adults could care less. I've found them in with my chickens without them causing trouble.
Yep, to what Jean said. I've got my oldest Guineas in a seperate coop, my teenagers in a pen that they can not access the main chicken coop but can go out a seperate door to go outside. Very soon I'll have another group that are in with the chickens that will have to be seperated in to a...