Bottlenose dolphins make many different sounds that have been recorded and described by researchers for over 60 years. This species, Tursiops truncatus, is arguably the most studied marine mammal. They have the ability to hear and produce sounds over a range of at least 150 kilohertz (kHz). Although the human hearing is limited in bandwidth to less than 20 kHz, dolphin sounds have historically been described as humans perceive them (e.g. whistles, squeals, buzzes, barks, quacks, pops, etc.). Often the same names have been used for different sounds and different names have been used for sounds that are apparently the same. In this review, we try and summarize the dolphin sound literature and provide standardized spectrograms where possible. Our goal is to provide a foundation for future research to build upon by providing a tool for identifying whether a sound has been described before. Novel sound types can then be recognized. Also, we encourage future studies that show when dolphins perceive two sound types as different. Detailed reports linking sound and behaviour are also essential. Only then can we have a complete idea of the dolphin repertoire and begin to understand how they use sound for communication.

This report describes the epimeletic (or “caregiving”) behavior produced by members of a group of Atlantic bottlenose dolphins ( Tursiops truncatus) and the possible role of the ailing animal’s...

Biphonation, deterministic chaos, sidebands and subharmonics are four non-linear phenomena (NLP) that have been identified as common additions in the phonations of animals. NLP have been hypothesised to communicate urgency, caller identification, fitness and arousal/valence states for a variety of species but have yet to be studied in detail for bottlenose dolphins. For this study, the signature whistles of nine bottlenose dolphins residing at the US Navy Marine Mammal Program (MMP) were opportunistically recorded during routine periods of separation from conspecifics. NLP were found to be common additions onto the spectral structure of signature whistles, occurring in 53% of recorded whistles (340/642). Sidebands were the most common NLP type produced. Although less frequently emitted, biphonations were characterised by a significantly longer persistence than the other NLP types. Age had a negative correlation with overall NLP presence, and more specifically, sideband presence. Individual differences in NLP use existed between dolphins; however, all dolphins were recorded producing a minimum of two NLP types. We describe NLP prevalence in dolphin whistles in order to provide a useful baseline for continued research to further identify changes in NLP across behavioural and/or health conditions.

Most commonly, animal communication systems are driven by shared call repertoires, with some individual distinctiveness encoded as a byproduct of voice cues. We provide evidence that bottlenose dolphins produce both individually distinctive whistles, and a shared whistle type. A stereotyped whistle contour (termed the group whistle) is shared by five bottlenose dolphins that have lived, worked, and traveled together for at least 21 years. These five dolphins are members of a group of eight dolphins that work as a specialized team for the Navy Marine Mammal Program. Each dolphin is routinely recorded during periods when an individual is isolated from the others in above ground pools as part of their routine training. Each of the eight dolphins has an individually distinctive signature whistle. In addition, at least five of these dolphins share a distinct non-signature whistle type. This shared whistle contour was produced an average of 22.4% +/- 9.0% of the time during periods in which individuals were isolated. During these isolations the signature whistle was produced an average of 42.9% +/- 11.9% of the time. This is consistent with decades of signature whistle research. A group of 10 naïve observers rated the similarity of the different whistle contours. The observers rated the group whistle contour produced by all five dolphins as highly similar (P < 0.01). Their ratings further showed that the signature whistles of the five dolphins were very different (P < 0.01). These findings were further supported by discriminant function analyses. That said, the shared whistle contours still exhibited individual differences which may allow conspecifics to identify the producer even when a whistle contour is shared among multiple dolphins. This is the first in-depth analysis of a non-signature whistle type shared among multiple conspecifics.

Animal sounds are commonly used by humans to infer information about their motivations and their health, yet, acoustic data is an underutilized welfare biomarker especially for aquatic animals. Here, we describe an acoustic monitoring system that is being implemented at the U.S. Navy Marine Mammal Program where dolphins live in groups in ocean enclosures in San Diego Bay. A four-element bottom mounted hydrophone array is used to continuously record, detect and localize acoustic detections from this focal group. Software provides users an automated comparison of the current acoustic behavior to group historical data which can be used to identify periods of normal, healthy thriving dolphins, and allows rare instances of deviations from typical behavior to stand out. Variations in a group or individual’s call rates can be correlated with independent veterinary examinations and behavioral observations in order to better assess dolphin health and welfare. Additionally, the monitoring system identifies time periods in which a sound source from San Diego Bay is of high-enough amplitude that the received level at our array is considered a potential concern for the focal animals. These time stamps can be used to identify and potentially mitigate exposures to acoustic sources that may otherwise not be obvious to human listeners. We hope this application inspires zoos and aquaria to innovate and create ways to incorporate acoustic information into their own animal welfare management programs.