@ygritte: you can kiss a happy-hen-paradise goodbye with the addition of a rooster; laid-back Happy-day chicken TV will transform into a chicken coop soap opera, a stormy and intense adventure of never ending challenge and bitter-sweet resolution. Life without roosters is Soooooo less complicated.
To the point, however: I had two unplanned, surprise hatches last summer: one from my Silkies, and one from my barnyard mutt hen. They were already running all over the place before I noticed them and started worrying. The Silkie chicks, especially, were out of control (I thought) running around with the "big guys;" they'd get through the pen fencing running hither and thither, and the Mama Silkies could not get through the fence to be with them. One of the chicks disappeared one day, and I took the pen fencing down as a lost cause. These chicks co-habited with their sires - and a small group of BIG Light Sussex cockerels, as well. Not one of the adult males ever made a move to hurt the chicks, nor do they now, now that they are full grown. Meanwhile, the barnyard hen kept a tight rein on her chicks. She free ranged them and showed them all the ropes. She took them over to visit a large cockerel I'd isolated, to eat from his feed dish and get underfoot. You should have seen me hollering. But you know, they were perfectly safe with him. After their first or second juvenile molt, though, she kicked them out of the Dogloo and became their worst enemy. One of the Light Sussex cocks adopted the whole bunch as his own, and now has his wings full managing a flock of 8 independent hens and 3 Wannabe-papas cockerels. It's a happy ending, I think.
I am not recommending you keep Roos with your chicks. I'm just saying it might not be disastrous if they accidentally got loose with the males. I've read others say as much.
