Whether they have any extant function or not, they have lost their former function and in that sense they do fit the definition of vestigiality. Vestigial structures are often called vestigial organs, although many of them are not actually organs.
There are quite a few birds famous for doing ritualized mating dances, so I would only list 5: The Red Capped Manakin, The Black-footed albatross, The Western and Clark's grebe, The Superb bird of Paradise, & The Victoria's riflebird.
Flightless feathered family. The cassowary is a large, flightless bird most closely related to the emu. Although the emu is taller, the cassowary is the heaviest bird in Australia and the second heaviest in the world after its cousin, the ostrich.It is covered in dense, two-quilled black feathers that, from a distance, look like hair.he cassowary is rightfully considered the most dangerous bird in the world! Each 3-toed foot has a dagger-like claw on the inner toe that is up to 4 inches (10 centimeters) long!