The broadband social acoustic signaling behavior of spinner and spotted dolphins

Abstract

Efforts to study the social acoustic signaling behavior of delphinids have traditionally been restricted to audio-range (<20 kHz) analyses. To explore the occurrence of communication signals at ultrasonic frequencies, broadband recordings of whistles and burst pulses were obtained from two commonly studied species of delphinids, the Hawaiian spinner dolphin (Stenella longirostris) and the Atlantic spotted dolphin (Stenella frontalis). Signals were quantitatively analyzed to establish their full bandwidth, to identify distinguishing characteristics between each species, and to determine how often they occur beyond the range of human hearing. Fundamental whistle contours were found to extend beyond 20 kHz only rarely among spotted dolphins, but with some regularity in spinner dolphins. Harmonics were present in the majority of whistles and varied considerably in their number, occurrence, and amplitude. Many whistles had harmonics that extended past 50 kHz and some reached as high as 100 kHz. The relative amplitude of harmonics and the high hearing sensitivity of dolphins to equivalent frequencies suggest that harmonics are biologically relevant spectral features. The burst pulses of both species were found to be predominantly ultrasonic, often with little or no energy below 20 kHz. The findings presented reveal that the social signals produced by spinner and spotted dolphins span the full range of their hearing sensitivity, are spectrally quite varied, and in the case of burst pulses are probably produced more frequently than reported by audio-range analyses.

Variation in the emission rate of sounds in a captive group of false killer whales Pseudorca crassidens during feedings: possible food anticipatory vocal activity?

“…During feeding, part of the fi sh was tossed in the water to feed the mother and calf, a method which might have triggered a heightened production of clicks by the whales (Dreher, 1966;dos Santos and Almada, 2004) that used the fi sh as a target. Moreover, the fi sh tossed into the tank might have developed competition among the animals with an increase in production of burst pulses (Overstrom, 1983;Connor and Smolker, 1996;Herzing, 1996;Lammers et al, 2003;Nowacek, 2005). Moreover, Ridgway et al (2014) suggested that burst pulses produced during feeding sessions might be considered as food calls with emotional content.…”

“…The type of sounds produced by false killer whales are included either in the traditional categories such as whistles, clicks, and burst-pulses, or in the class of sounds with intermediate acoustic characteristics (graded sounds=click trains and whistles are at the opposite ends of a continuum) (Murray et al, 1998a, b) . It has been suggested that sounds with graded structure may communicate the animal's behavioral states, while acoustic emissions included in well-defi ned categories would indicate a unique function of the signals (Lammers et al, 2003: spotted dolphins, Stenella frontalis ; spinner dolphins, Stenella longirostris ; Herzing, 1996: spotted dolphins, Stenella frontalis ; Rehn et al, 2007, 2011Weir et al, 2007: sperm whales, Physeter macrocephalus ;Murray et al, 1998a, b: false killer whales, Pseudorca crassidens ). Even though diff erent studies have been performed on the characteristics of false killer whales' sounds (Busnel and Dziedzic, 1968;Kamminga and van Velden, 1987;Thomas et al, 1988;Au et al, 1995;Murray et al, 1998a, b;Rendell et al, 1999;Supin et al, 2003Supin et al, , 2004Supin et al, , 2005Madsen et al, 2004;Nachtigall and Supin, 2008), there is no information available on the eff ects of the controlled environment on the acoustic activity of this species of dolphin.…”

Vessel noise effects on delphinid communication

“…Masking impacts were modelled on the fundamental whistle contour because this has been shown to convey important information between animals (Janik et al 2006). It is possible that some species put more acoustic energy into the harmonics than in the fundamental contour (Lammers et al 2003), but it is unknown how information is distributed between the fundamental contour and the harmonics. Our assumption that noise masking narrow band signals is integrated by the auditory system over one-third octave bands roughly corresponds to the critical bandwidths found in bottlenose dolphins (Johnson 1968).…”

Exploration of Horizontal Information Transmission through Social Learning in Juvenile Atlantic Spotted Dolphins (Stenella frontalis)

“…The bottom is primarily sandy, with zones of rock, reef and patches of seagrass (Thalassia testudimum). The life history, including non-invasive genetic analysis, (Elliser & Herzing, 2012, 2013, 2016a, 2016bGreen, Herzing & Baldwin, 2007 and the development and use of social and acoustic behaviors of this community of Atlantic spotted dolphins have been documented extensively Herzing, 2000Herzing, , 2004Herzing, , 2005Herzing & Brunnick, 1997;Herzing & dos Santos, 2004;Herzing & Johnson, 1997;Herzing, Moewe & Brunnick, 2003;Lammers, Au & Herzing, 2003;Miles & Herzing, 2003;Welsh & Herzing, 2008).…”