In my yard and coops I have. Muscovies, sumatras. silkies, Barred rocks, Polish, Beltsvilles, Boubon reds and EE's. Out of all these birds, my Belts hens are the nastiest of them all. It doesn't seem to matter how slowly I integrate new birds in with the flock, as soon as they are finally allowed out of their Temporary, getting to know the flock pens. The hens(not the tom) chase them relentlessly for days! The Bourbons don't bother them at all. Are the belts in general a more aggressive breed? ( Ours have never been aggressive to us, just the new birds).