This pair has just finished copulating, and they are doing the post-coital unison prancing that is part of the mating ritual of this species. Another pair doing the same dance, same morning, nearby place is shown at http://www.pbase.com/image/143160311 . Avocets have a similar mating ritual, see them doing their promenade at http://www.pbase.com/tgrey/image/142991310 .