My Silkie was broody (& not laying eggs anymore) for 4 days before I stuck 11 Houdan babies under her. Of course, I put her in the brooder box and stuck a bunch of food under her nose so she was so busy eating that she paid no attention to the chicks. Also, I took her out of the nest she was in (with her wooden eggs) and brought her in the house - basically shook up the whole project she had going.
She was experienced in fostering when I got her - perhaps the difference is in when they go broody for the first time?
Admittedly, I had no idea what she would do and so started with just 2 chicks. When she ignored them (that was a good sign), I added more. This was the first time I'd tried using a foster momma and everything was going well until day 12 when one was strangled in some matted fluff. Took her out, bathed her completely, cut off any and all mats I could find, blow-dried her thoroughly, and she couldn't get back to those babies fast enough.
As for the original question - it seemed as if 11 was too many because there always seemed to be at least 2 or 3 that got shoved out, but after a few days, she and the chicks worked it out so that she actually covered all of them completely.
Hope this helps!
