I have five Buff Orp pullets from McMurray. Three of them have 4 or 5 tail feathers with a dark brown pattern on them. At first I thought it was dirt, but it's not. It looks like brindle coloring on a dog, or on what I've seen of Ameraucana color patterns. Is this typical of Buff Orps? Or do these girls have mixed grandparents? Does this happen at professional hatcheries? Thank you in advance.