Feeding at a high pitch: Source parameters of narrow band, high-frequency clicks from echolocating off-shore hourglass dolphins and coastal Hector’s dolphins

Abstract

Toothed whales depend on echolocation for orientation and prey localization, and source parameters of echolocation clicks from free-ranging animals therefore convey valuable information about the acoustic physiology and behavioral ecology of the recorded species. Recordings of wild hourglass (Lagenorhynchus cruciger) and Hector's dolphins (Cephalorhynchus hectori) were made in the Drake Passage (between Tierra del Fuego and the Antarctic Peninsular) and Banks Peninsular (Akaroa Harbour, New Zealand) with a four element hydrophone array. Analysis of source parameters shows that both species produce narrow band high-frequency (NBHF) echolocation clicks. Coastal Hector's dolphins produce clicks with a mean peak frequency of 129 kHz, 3 dB bandwidth of 20 kHz, 57 micros, 10 dB duration, and mean apparent source level (ASL) of 177 dB re 1 microPa(p.-p.). The oceanic hourglass dolphins produce clicks with mean peak frequency of 126 kHz, 3 dB bandwidth of 8 kHz, 116 micros, 10 dB duration, and a mean estimated ASL of 197 dB re 1 microPa(p.-p.). Thus, hourglass dolphins apparently produce clicks of higher source level, which should allow them to detect prey at more than twice the distance compared to Hector's dolphins. The observed source parameter differences within these two NBHF species may be an adaptation to a coastal cluttered environment versus a deep water, pelagic habitat.

Echolocation in sympatric Peale's dolphins (Lagenorhynchus australis) and Commerson's dolphins (Cephalorhynchus commersonii) producing narrow-band high-frequency clicks

“…In line with what has been shown for harbour porpoise signals (Hansen et al, 2008), it is very likely that most of the low-frequency sounds recorded by Schevill and Watkins (Schevill and Watkins, 1971) were in fact distortion products of the NBHF signals, created by clipping the analog tape recorder/amplifier. The present results are consistent with the recent finding that the sister species of the Peale's dolphin, the hourglass dolphin, also produces NBHF signals (Kyhn et al, 2009), supporting the suggested close phylogenetic affinity of these two species to the dolphin genus Cephalorhynchus (May-Collado and Agnarsson, 2006;Tougaard and Kyhn, 2010).…”

“…Kyhn and colleagues (Kyhn et al, 2009) showed that offshore hourglass dolphins produce clicks of higher source levels than the coastal Hector's dolphins. Hourglass dolphins are oceanic and may thus have evolved to generate a higher source level than coastal NBHF species as prey patches are more widely distributed in the open sea as opposed to shallow coastal habitats where the interprey distances are smaller, and where clutter levels likely are higher.…”

“…To minimize the risk of including distorted off-axis clicks in the analysis (Madsen and Wahlberg, 2007) we applied a set of criteria to determine clicks as being on-axis by following the methods of Villadsgaard and colleagues (Villadsgaard et al, 2007) and Kyhn et al (Kyhn et al, 2009): On-axis clicks should be: (i) recorded on all six channels; (ii) part of a scan -that is, a series of clicks closely spaced in time, normally first increasing then decreasing in amplitude (sensu Møhl et al, 2003); (iii) of maximum amplitude in the scan; (iv) of maximum amplitude on one of the four middle hydrophone channels; and (iv) such that the direct path of the click had to be stronger than any trailing bottom or surface reflections. Furthermore, the localization error (Villadsgaard et al, 2007) could not give rise to an r.m.s.…”

“…The groups producing these strikingly similar NBHF clicks include the Phocoenidea family (Møhl and Andersen, 1973;Akamatsu et al, 1998;Villadsgaard et al, 2007), the Cephalorhynchus genus (Kamminga and Wiersma, 1982;Dawson and Thorpe, 1990;Kyhn et al, 2009) within the dolphin family [including the hourglass dolphin (Lagenorhynchus cruciger)] and the pygmy sperm whale (Madsen et al, 2005). Furthermore, the Francicana river dolphin (Pontoporia blainvillei) (von Fersen et al, 2000) is proposed to use NBHF clicks, but only the peak frequency and -3dB bandwidth was stated by the investigators (von Fersen et al, 2000).…”

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

“…The clicks of Heaviside's dolphins conform to the model of species using NBHF clicks (Morisaka & Connor, 2007). Heaviside's dolphin clicks were reported to have a mean centroid frequency of 125 kHz (range 118 to 132 kHz), click duration of 74 μs, inter-click intervals ranging from 2 to 113 ms (Morisaka et al, 2011), and overall characteristics similar to the clicks of other Cephalorhynchus species (Kamminga & Wiersma, 1982;Dawson & Thorpe, 1990;Kyhn et al, 2009Kyhn et al, , 2010Götz et al, 2010).…”