The feather test does not hurt, we just never did it. I know with amazons, the males generally have a slightly flatter head, as JT says. This was hard to see until my "princess" was next to "her" dna'd sister, whose head was very rounded, and the sister was much bigger. With Dobby, our Maxi, I do not see the degree of flatness on his head, and his body size is large. Since these are not the same species, but related, I bet the flat head thing is true, just maybe not so obvious.