In other aspects of chicken-keeping you seem to trust the chickens to make the right decision for themselves. Why not in this one?A problem that I don't have an answer for is C keeps putting bird seed in the feeder and they prefer this to the pellets.
(Incidentally, you call it bird seed, but when you showed a photo [who knows how many pages back?!] it looked like mostly grain to me, with a variety of seeds added.)
Apart from my natural curiosity, I ask because I received a copy of Katie Thear's Free range poultry for Christmas, and she reports a record kept by a utility breeder in 1993 wherein Wyandottes had free access to both wheat and layer's mash, and in both pens they chose to eat 3-4 times more wheat than mash. (They laid average 244 eggs in this year BTW.)