Understanding that the studies were designed for prime age commercial layers, about 4% calcium +/- but averaging around 4% is what needed to provide a production red, leghorn, or the like its calcium needs while laying. There is some variation by individual, but you needn't panic if you are only getting 3.6% average or 4.5% average for your hens, if you feed them seperately.
The calcium needs of pre-production birds of all ages, and roosters throughout their lifespan, is about 1%+/- within a narrower range. Typically 0.9 - 1.2 %, with at least 40% as much potassium (0.4%) but benefiting them up to about 0.6% potassium.
Over longer time scales, higher calcium abmounts have the potential to be damaging particularly to hatchlings and adoloscents, but also to roos. How much damage depends on time, dosage, and when the excess began - much like smoking - some people suffer no ill effects, some people get mild cancers, some people genm numerous, and severe, cancers. No predicting it in advance in any individualy - but statistically, the more you smoke, the younger you start, the less filtered the cigarettes, the more likely you are to develop one or more severe forms of cancer.
From those well understood studies principles, and analogies, we infer that bird that produce smaller eggs than prime production layers, or less frequent eggs than prime production layers, (or both) need less calcium to support their egg shell production. How much less??? Nobody studies that - there's no money in the knowledge.
Whch is part of why so many of us BYCers recommend feeding an "all flock"-type formulation (around 1% calcium +/-) together with free choice calcium (usually in the form of oyter shell), becuase studies have repeatedly shown that chicks are generally (there are individual exceptions, - but generally) able to self regulate their calcium needs when a source is available.
