9ISSF, 2Form. "subspecies that exhibit marked variation in plumage pattern and coloration (gray vs. black)" per BOW. The sheer variety of pattern makes me think a split is in the future. Plumage varies, with breeding (MAR-AUG) and non-breeding (SEP-FEB). Main difference is breeding has richer, blacker coloration. M/F similar, some difference in coloration but doubt this is easily gauged unless already familiar with WHWA.