How toothed whales echolocate to find and capture prey

Abstract

Sperm and beaked whales are deep-diving toothed whales whose echolocation behavior has been studied using tags that record sound and whale orientation. Combining orientation data from tagged clicking whales with acoustic localization data from a towed hydrophone array allowed measurement of the three-dimensional beam pattern of regular clicks from sperm whales. These data confirm Mohl’s bent horn hypothesis for sound production in sperm whales. During deep foraging dives, beaked whales produce several thousand regular clicks with interclick intervals (ICI) between 0.2 and 0.4 s. These search clicks have a distinctive FM upsweep from 25 to 55 kHz and a pulse length of 200–250 μs. The process of echolocating on prey can be divided into search, approach, and capture phases. The approach phase starts when a series of echoes from prey is detected. The capture phase starts when the target is about 2–5 m away, with a terminal buzz with click rates to ICIs of about 0.01 s. Tagged whales do not adjust their ICI to match range to target, nor do they adjust click level to maintain a constant echo level, but rather have a bimodal echolocation pattern using two kinds of clicks each with a typical ICI.