Three years ago I was guiding on the west coast of the Yucatan Peninsula in Mexico. Among the 200+ species we enjoyed on that tour was this distinctive silhouette of a Turquoise-browed Motmot:
It's been shown that males do this more during the breeding season (which suggests it's a sexual selection trait) but also, and perhaps more interestingly, both sexes do this year-round in the presence of a predator.
This latter reason, a predator-elicited display, is thought to function as a pursuit-deterrent signal. Basically, the bird is telling a potential predator "I see you already, and so it's a waste of your time to try to ambush me."