The Pair-Formation Displays of the Western Grebe

In this paper we describe and illustrate the pair-formation displays of the Western Grebe (Aechmophorus occidentalis), examining their structural variation, social contexts, and probable evolutionary origins and functions. Most displays are performed mutually by two or more individuals and occur in elaborate and predictable sequences or "ceremonies." One of these, the "Rushing Ceremony" is performed by either two males, a male and a female, or several males and a female. The "Weed Ceremony," on the other hand, occurs later in the pairing sequence and always involves a male and a female. Finally, the "Greeting Ceremony," used by pairs coming together after being separated, appears to be an abbreviation of the above two ceremonies with the energetic, core displays left out. We examine the temporal and spatial coordination between individuals involved in each of these ceremonies. Most displays and ceremonies of Western Grebes differ greatly from those described for other grebe species, which supports morphological evidence for retaining the Western Grebe in a separate genus. The similarity of the Weed Ceremony to that of some species of Podiceps supports morphological evidence for considering the Western Grebe more closely related to that genus than to any other.