Vocal behavior of male sperm whales: Why do they click?

Off Kaikoura. New Zealand, we recorded individually identified male sperm w hales (Physeter macrocephalus) for entire dive cycles in order to investiga te vocal behavior of individual whales and to examine possible functions of sperm whale clicks. In our study, sperm whales were almost always silent a t the surface. They consistently started clicking within 25 s after fluking -up and diving. During the first 10 s of clicking, interclick intervals wer e significantly correlated with water depths at the location of fluke-up. T he first "creak" was produced on average 7.5 min into a dive. Interclick in tervals usually decreased substantially before clicks turned into ''creaks, '' The highest click rate recorded in this study was 90.9 click/s, and clic ks-within-creaks were much shorter than "usual clicks" (mean of 3.6 ms vers us 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 rem ains puzzling. The results of this study suggest that usual clicks and crea ks are both used for echolocation purposes, the former to gather informatio n about acoustically reflective features and the latter to detect prey. (C) 2001 Acoustical Society of America.