Abstract
Off Kaikoura, New Zealand, we recorded individually identified male sperm whales (Physeter macrocephalus) for entire dive cycles in order to investigate vocal behavior of individual whales and to examine possible functions of sperm whale clicks. In our study, sperm whales were almost always silent at the surface. They consistently started clicking within 25 s after fluking-up and diving. During the first 10 s of clicking, interclick intervals were significantly correlated with water depths at the location of fluke-up. The first “creak” was produced on average 7.5 min into a dive. Interclick intervals usually decreased substantially before clicks turned into “creaks.” The highest click rate recorded in this study was 90.9 click/s, and clicks-within-creaks were much shorter than “usual clicks” (mean of 3.6 ms versus 17 to 30 ms). The number of creaks per minute of dive and the length of a dive were significantly correlated. On average, sperm whales were silent for the last 3.6 min before surfacing. Short sequences of “surface clicks” (3 to 8 metallic clicks with mean interclick interval of 5.5 s) were often produced at the end of a dive (in 57% of the dives), but their function remains puzzling. The results of this study suggest that usual clicks and creaks are both used for echolocation purposes, the former to gather information about acoustically reflective features and the latter to detect prey.