Ear tuft
Ear tufts are skin projections covered in feathers found in some bird species, most notably various species of owl, vaguely resembling mammalian ears, but unrelated to the animal's hearing.  Their function remains uncertain.

About
Theories about their function range from improved ability to camouflage, aiding in finding a suitable mate, to giving a more threatening appearance to discourage predators.

In the Araucana chicken breed, ear tufts are a mutation. It causes a skin projection covered in feathers to appear on the sides of the head near the ears. This mutation is dominant semi-lethal.  Consequently, ear tufts are very unusual and difficult to breed, as most Araucanas are hatched without tufts.