Feathers and the Birds-of-Paradise
Display feathers are highly evolved versions of a basic feather. They no longer have the standard structure of a central quill and a vane made of tiny interlocking barbs. They've evolved into fluffy plumes or stiff wires, some with hard ornaments or tabs. These radical changes, and the muscles that let the bird move them, serve no purpose other than to improve the male's chances during courtship. The Cornell Lab's Ed Scholes explains: