What You See Is Not What You Hear: The Relationship Between Odontocete Echolocation Click Production and Hearing

Abstract

The improvement in tagging technology and passive listening devices has allowed researchers to measure the echolocation clicks of many species of free-ranging odontocetes. Although the data collected by these instruments provide valuable information on the clicks these animals produce, these tags cannot provide information on the hearing abilities of these species. A reasonable assumption is that animals produce sounds in the same frequency regions of hearing, but recent studies suggest this may not be the case. The development of a portable auditory evoked potential system has allowed for recent hearing measurements of stranded and rehabilitated animals. The white-beaked dolphin (Lagenorhynchus albirostris) has the most sensitive hearing between 45 and 128 kHz (Nachtigall et al. 2008), but free-ranging individuals produce echolocation clicks with considerable energy in frequencies up to 250 kHz (Rasmussen and Miller 2002). Risso’s dolphin (Grampus griseus) has the most sensitive hearing between 22 and 90 kHz (Nachtigall et al. 2005), but free-ranging individuals produce echolocation clicks with considerable energy in frequencies up to 120 kHz (Madsen et al. 2004).