Biosonar performance of foraging beaked whales (Mesoplodon densirostris)

Abstract

Toothed whales (Cetacea, odontoceti) emit sound pulses to probe their surroundings by active echolocation. Noninvasive, acoustic Dtags were placed on deep-diving Blainville's beaked whales (Mesoplodon densirostris) to record their ultrasonic clicks and the returning echoes from prey items, providing a unique view on how a whale operates its biosonar during foraging in the wild. The process of echolocation during prey capture in this species can be divided into search, approach and terminal phases, as in echolocating bats. The approach phase, defined by the onset of detectable echoes recorded on the tag for click sequences terminated by a buzz, has interclick intervals (ICI) of 300-400·ms. These ICIs are more than a magnitude longer than the decreasing two-way travel time to the targets, showing that ICIs are not given by the two-way-travel times plus a fixed, short lag time. During the approach phase, the received echo energy increases by 10.4(±2)·dB when the target range is halved, demonstrating that the whales do not employ rangecompensating gain control of the transmitter, as has been implicated for some bats and dolphins. The terminal/buzz phase with ICIs of around 10·ms is initiated when one or more targets are within approximately a body length of the whale (2-5·m), so that strong echo returns in the approach phase are traded for rapid updates in the terminal phase. It is suggested that stable ICIs in the search and approach phases facilitate auditory scene analysis in a complex multi-target environment, and that a concomitant low click rate allows the whales to maintain high sound pressure outputs for prey detection and discrimination with a pneumatically driven, bi-modal sound generator.

Clicking for calamari: toothed whales can echolocate squid Loligo pealeii

“…However, even when using a hypothetical TS that is 15 dB lower than that cited by Fristrup & Harbison (2002), deep sea squid appear to be acoustically detectable by echolocating toothed whales at ranges equivalent to many whale body lengths. The mesopelagic prey community often forms a dense patch or layer of organisms (Isaacs et al 1974, Madsen et al 2005a, which in some cases will render biosonar detection of prey clutter-limited, rather than noiselimited (Fig. 1).…”

“…All toothed whale species carry homologous ultrasound-producing structures in their foreheads (Cranford et al 1996), and recent data from free-ranging toothed whales provide strong evidence that they use echolocation as their primary sensory modality for finding and catching prey , Miller et al 2004, Akamatsu et al 2005, Madsen et al 2005a, Watwood et al 2006. Sound is therefore a key parameter in the sensory interface between toothed whales and their prey, and should be considered when evaluating the behavioral ecology, sensory physiology, and life history strategies of the large number of marine organisms preyed upon by these echolocating predators.…”

Effective beam pattern of the Blainville's beaked whale (Mesoplodon densirostris) and implications for passive acoustic monitoring

“…Much of what is known about the foraging behavior and sound production of this species has come from sound and movement recording tags attached to the dorsal surface of animals Madsen et al, 2005;Zimmer et al, 2005). Similar data have also been obtained from Cuvier's beaked whale (Ziphius cavirostris), another species considered to be sensitive to sonar (D'Amico et al, 2009).…”

Using Static Acoustic Monitoring to Describe Echolocation Behaviour of Heaviside’s Dolphins (Cephalorhynchus heavisidii) in Namibia

“…Feeding-buzz ratio (FBR) has previously been used as an indicator of potential feeding behaviour for odontocetes (Todd et al, 2009). The terms feeding buzz or click burst have been used to describe the very fast click trains (i.e., with small ICI values) produced as cetaceans or bats approach and capture targets such as prey items (e.g., Goodson et al, 1988Goodson et al, , 1994Miller et al, 1995;Johnson et al, 2004Johnson et al, , 2006Johnson et al, , 2008Akamatsu et al, 2005;Madsen et al, 2005;Melcón et al, 2007;Verfuβ et al, 2009). In the terminal phase of the approach of harbour porpoises to prey items, the ICI is first reduced from about 50 ms to intervals below 10 ms and is then kept short and constant at values between 1.4 and 1.6 ms (Verfuβ et al, 2009).…”