Fig. 2. Scatter plots of dive duration (A,C) and vertical speed (B,D) as functions of dive depth for all dives deeper than 20 m recorded on Ziphius cavirostris (A,B) and Mesoplodon densirostris (C,D). The plots in A and C show the surface-to-surface dive duration (dots) and the interval from the start to the end of regular clicking (unfilled triangles) in each dive. The absence of dive depths between 450 and 700 m for both species and the observation that only dives deeper than this range have consistent vocalizations leads us to define these as deep foraging dives (DFD). The plots in B and D show vertical speed (i.e. depth rate) as a function of dive depth during descents (downwards pointing black triangle) and ascents (upwards pointing unfilled triangle). The difference between descent and ascent rate for DFDs is apparent.