King Penguins have 70 feathers per every square inch. The outer layer of feathers are oiled and waterproof, unlike the feathering of a duck, which reduces the amount of water absorbed that would otherwise increase their weight. The inner three layers are down feathers, very effective insulation. Their eyes are highly adapted to the type of hunting they do at depth to fish for lanternfish. According to Wiley's online library: King Penguins forage at depths where ambient light levels, even during the day, can fall below the equivalent of terrestrial starlight. Under these conditions, the birds must rely upon the detection of light from the photophores of their prey.