Estimated communication range of social sounds used by bottlenose dolphins (Tursiops truncatus)

Abstract

Bottlenose dolphins, Tursiops truncatus, exhibit flexible associations in which the compositions of groups change frequently. We investigated the potential distances over which female dolphins and their dependent calves could remain in acoustic contact. We quantified the propagation of sounds in the frequency range of typical dolphin whistles in shallow water areas and channels of Sarasota Bay, Florida. Our results indicated that detection range was noise limited as opposed to being limited by hearing sensitivity. Sounds were attenuated to a greater extent in areas with seagrass than any other habitat. Estimates of active space of whistles showed that in seagrass shallow water areas, low-frequency whistles (7-13 kHz) with a 165 dB source level could be heard by dolphins at 487 m. In shallow areas with a mud bottom, all whistle frequency components of the same whistle could be heard by dolphins travel up to 2 km. In channels, high-frequency whistles (13-19 kHz) could be detectable potentially over a much longer distance (> 20 km). Our findings indicate that the communication range of social sounds likely exceeds the mean separation distances between females and their calves. Ecological pressures might play an important role in determining the separation distances within communication range.

Estimated communication range and energetic cost of bottlenose dolphin whistles in a tropical habitat

“…At short ranges, this corresponds well with the transmission loss predicted using the Marsh and Shulkin (1962) model for continuous sounds as employed by Janik (2000) and Miller (2006). The existence of sound channels might increase the transmission of signals drastically for very specific frequencies (Quintana-Rizzo et al, 2006). However, sound transmission in such channels is often unpredictable and varied, and received levels can change quickly even over short distances and depths (QuintanaRizzo et al, 2006).…”

“…Noise levels in this study were obtained under ideal, lownoise conditions (Sea State 0: flat sea with no vessels and no wind), so if anything, the active space will likely be lower than reported here due to increased noise from wind, waves and rain. Together, these results imply that communication range of tropical, coastal dolphins is inherently short-range where 50% of the whistles are unlikely to be detected beyond a range of 800 m, more than an order of magnitude lower than some previous estimates for delphinids (Janik, 2000;Miller, 2006), and much closer to the ranges estimated in Sarasota Bay (Quintana-Rizzo et al, 2006).…”

“…The noise levels in this study are about 6 dB lower than used to model communication ranges in Sarasota (Quintana-Rizzo et al, 2006), but are comparable to noise levels found in other subtropical habitats with snapping shrimp (Au et al, 1985). Noise levels in this study were obtained under ideal, lownoise conditions (Sea State 0: flat sea with no vessels and no wind), so if anything, the active space will likely be lower than reported here due to increased noise from wind, waves and rain.…”

Seasonal Trends in Acoustic Detection of Marine Mammals in Baffin Bay and Melville Bay, Northwest Greenland + Supplementary Appendix 1 (See Article Tools)

“…Sounds below 1 kHz (typical of mysticete calls) have significantly less seawater absorption loss than sounds above 10 kHz (typical of odontocete calls) and thus can be detected at greater distances . Mysticete calls are commonly detected at ranges of several tens of kilometres on a single hydrophone , while odontocete clicks and whistles can be detected at ranges of 1 -6 km (Quintana-Rizzo et al, 2006;Wang et al, 2006;Jensen et al, 2012;Ainslie, 2013). Stafford et al (2012a) and Marcoux et al (2012) discuss the large overlap in vocal repertoires of the two Monodontid species (beluga whales and narwhals) that share migration routes in Baffin Bay (Heide-Jørgensen et al, 2003a, c).…”

Sensory Perception in Cetaceans: Part I—Current Knowledge about Dolphin Senses As a Representative Species

“…However, the active space of a sound depends (among other factors such as its frequency) on bottom substrate and water depth. For example, the same call is perceived at less than 200 m in a shallow sea grass area of 1.6 m depth, but up to more than 6 km in a sandy bottom area of 3.5 m depth (Quintana-Rizzo et al, 2006).…”