Do you mean will they not brood when the flock is large? Animals are all about passing genetics on. That's why broody hens sometimes won't take foster chicks that they know aren't theirs. They want their genetics to go on, not the hen eating next to them. Those hormones cause a hen to go broody, not them thinking 'the flock is getting smaller, we need more chicks'If there are too many broody hens and some die won’t they eventually select for flock balance?