Low Frequency Dolphin Sounds

Mar 25, 2012 No comments By

 

Barks, yelps, thunks, grunts, chirps, and squawks are little-studied and infrequent sounds emitted by different dolphin species.

They are called low frequency narrow band (LFN) sounds, and they seem to be associated with socializing, sexual, or aggressive behavior, or possibly foraging activities.

LFN sounds have  conservation implications because acoustic communication is particularly important in inshore areas where vision is often limited.

Dolphins are well known to emit whistles, echolocation, and burst-pulses.  Click here to hear samples.

  • Whistles are tonal signals, audible to humans, which have a social function.
  • Echolocation consists of short, high intensity pulses produced in rapid succession in “click trains,” and it is used for navigation and to capture prey.
  • A burst-pulse is acoustically similar to echolocation pulses, but with higher pulse rates.

How LFN sounds fit into the dolphin sound repertoire is unclear because LFN sounds infrequently are heard, and they are not often reported in the scientific literature.

A recently published article, however, focuses on LFN sounds, comparing them across dolphin populations in Sarasota Bay, Tampa Bay, and the Mississippi sound in the northern Gulf of Mexico.

This is important research because so little is know about the context LFN communication. The frequencies of these sounds are below what is normally thought of as the range of good hearing in bottlenose dolphins.

Noise from boat motors potentially could interfere with, or mask LFN sounds, thus limiting dolphin communication in areas with high motorboat use.  SDRP studies have shown that dolphins whistle more frequently when boats approach, but the context is unclear.

The research article was published in the Journal of the Acoustical Society of America.  SDRP Director Randall Wells as one of the co-authors, and former SDRP intern and graduate student Ester Quintana-Rizzo also is a co-author.

Simard, P., Lace, N., Gowans, S., Quintana-Rizzo, E., Kuczaj, II., S. A., Wells, R. S., & Mann, D. A. (2011), Low frequency narrow-band calls in bottlenose dolphins (Tursiops truncatus): Signal properties, function, and conservation implications J. Acoust. Soc. Am. 130, 3068  DOI:10.1121/1.3641442

Abstract

Dolphins routinely use sound for social purposes, foraging and navigating. These sounds are most commonly classified as whistles (tonal, frequency modulated, typical frequencies 5–10 kHz) or clicks (impulsed and mostly ultrasonic). However, some low frequency sounds have been documented in several species of dolphins. Low frequency sounds produced by bottlenose dolphins (Tursiops truncatus) were recorded in three locations along the Gulf of Mexico. Sounds were characterized as being tonal with low peak frequencies (mean 1⁄4 990 Hz), short duration (mean 1⁄4 0.069 s), highly harmonic, and being produced in trains. Sound duration, peak frequency and number of sounds in trains were not significantly different between Mississippi and the two West Florida sites, however, the time interval between sounds within trains in West Florida was significantly shorter than in Mississippi (t 1⁄4 p 3.001, p 1⁄4 0.011). The sounds were significantly correlated with groups engaging in social activity (F1⁄48.323, p1⁄40.005). The peak frequencies of these sounds were below what is normally thought of as the range of good hearing in bottlenose dolphins, and are likely subject to masking by boat noise.

 

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Behavior, Social Structure, and Communication

About the author

Blair Irvine, PhD, is retired and manages the SDRP website, serves as President of the non-profit Dolphin Biology Research Institute, and he volunteers as otherwise needed. He started the SDRP in 1970 with then-high school student Randy Wells. Blair led the research into the late-1970’s when Randy took over. After that, Blair's non-dolphin career was in the area of human behavioral health. With NIH support, much of his research was involved Internet interventions and training programs. His graduate degrees are in Zoology, Exercise Physiology, and Health Education.
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