The waxwing’s crest is used principally for courtship, raised almost to the vertical as part of a wider display directed towards a potential mate. The bird also lowers its tail and ruffles the feathers on its back, rump, belly and legs while adopting a near-horizontal posture. The display is very different from the stiff upright posture that a waxwing adopts when threatening a rival, in which the crest remains flat to the head.
The use of a crest for courtship is seen in many bird species, with some developing particularly elaborate plumage. The crest may also be used in threat display, perhaps communicating the socially dominant status of the individual making the threat and resolving the conflict without recourse to physical violence. On occasion, the display may even be directed towards a different species.