The mature Steller's sea eagle has mostly dark brown to black plumage, with strongly contrasting white on the lesser and median upper-wing coverts, underwing coverts, thighs, under-tail coverts and tail. Their diamond-shaped, white tails are relatively longer than those of the white-tailed eagle. The bold, pied coloration of adults may play some part in social hierarchies with other eagles of their own species during the nonbreeding season, although this has not been extensively studied. A very rare dark morph, once regarded as a separate subspecies "H. p. niger", lacks white in its plumage, except for the tail. The eyes, the bill, and the feet of adults are yellow.