“…Additionally, bubble trails frequently occur in temporal clusters and are not associated with all whistle types (Fripp, 2005(Fripp, , 2006. However, the precise function of the relationship of bubble trails to whistle types, behavioral states, and affective states is currently unclear, and more research is needed in this area (Fripp, 2005(Fripp, , 2006McCowan, 2006;McCowan & Reiss, 1995).…”