Calcium?

[avjudge]

while this is true, it misses the point that the poster is in a calcium rich environment, in which calcium sources (limestone, in this case) of appropraite size are readily available.

Yes, I will agree that in the presence of so much available limestone a chicken can probably easily take in all the calcium she needs. I was certainly unclear that I was only addressing the more general case of that first sentence I quoted, which I thought made it sound like any chicken anywhere should be able to find enough calcium without our help. Oops!