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Review of the Signature-Whistle Hypothesis for the Atlantic Bottlenose Dolphin
... These signature whistles comprise more than half of the whistles that wild bottlenose dolphins produce [6,7]. They are formed in the first year of the dolphin's life [8] and remain relatively stable over their lifetime [4,8]. These unique whistles have been used to both identify [9,10] and to estimate the number of individuals within small (< 100 individuals), resident [11][12][13] populations but less is known about their utility for larger, wide-ranging populations [2]. ...
... These signature whistles comprise more than half of the whistles that wild bottlenose dolphins produce [6,7]. They are formed in the first year of the dolphin's life [8] and remain relatively stable over their lifetime [4,8]. These unique whistles have been used to both identify [9,10] and to estimate the number of individuals within small (< 100 individuals), resident [11][12][13] populations but less is known about their utility for larger, wide-ranging populations [2]. ...
... Additionally, because sound with frequencies above 24 kHz could not be detected in our recordings, higher frequency signature whistles would have been missed in our analyses [41]. While an increase in maximum frequency in response to higher sound levels was found in some studies [29,42,43], the maximum frequency of some signature whistles in this region were high [8] and at the upper limit of our sampling frequency. Thus, alternative acoustic compensation strategies such as shortening the duration of signature whistles may have been necessary [44][45][46][47][48]. ...
Passive acoustic monitoring has improved our understanding of vocalizing organisms in remote habitats and during all weather conditions. Many vocally active species are highly mobile, and their populations overlap. However, distinct vocalizations allow the tracking and discrimination of individuals or populations. Using signature whistles, the individually distinct calls of bottlenose dolphins, we calculated a minimum abundance of individuals, characterized and compared signature whistles from five locations, and determined reoccurrences of individuals throughout the Mid-Atlantic Bight and Chesapeake Bay, USA. We identified 1,888 signature whistles in which the duration, number of extrema, start, end, and minimum frequencies of signature whistles varied significantly by site. All characteristics of signature whistles were deemed important for determining from which site the whistle originated and due to the distinct signature whistle characteristics and lack of spatial mixing of the dolphins detected at the Offshore site, we suspect that these dolphins are of a different population than those at the Coastal and Bay sites. Signature whistles were also found to be shorter when sound levels were higher. Using only the passively recorded vocalizations of this marine top predator, we obtained information about its population and how it is affected by ambient sound levels, which will increase as offshore wind energy is developed. In this rapidly developing area, these calls offer critical management insights for this protected species.
... Signature whistles are individual-specific, stereotyped whistles, distinct with their contour, first described by Caldwell & Caldwell (1965). They remain stable over years (Caldwell et al. 1989, dos Santos et al. 2005, even though some parameters, such as intensity, duration, and repetition, change slightly depending on stress or excitement levels (Caldwell et al. 1989, Esch et al. 2009). The development of a signature whistle takes 1-2 years. ...
... Signature whistles are individual-specific, stereotyped whistles, distinct with their contour, first described by Caldwell & Caldwell (1965). They remain stable over years (Caldwell et al. 1989, dos Santos et al. 2005, even though some parameters, such as intensity, duration, and repetition, change slightly depending on stress or excitement levels (Caldwell et al. 1989, Esch et al. 2009). The development of a signature whistle takes 1-2 years. ...
... Learning continues throughout dolphin life in adulthood, as they mimic other signature whistles (Tyack 1986 to address the individual , developing an association between a specific whistle and a dolphin (Caldwell et al. 1989. Copies of such whistles are similar in contour to the original, however differ in frequency parameters. ...
Vocal communication is the main mean of communication for cetaceans and some species developed vocal culture and traditions. They are maintained through both production and contextual learning, used to acquire two types of sounds: signature calls and songs. Signature calls are present only in species living in stable groups or fission-fusion society. They are used as an identification tool to maintain cohesion and contact with conspecifics. Songs are present in most baleen whales, but only humpback and bowhead whales change within and between seasons. They use vocal learning to conform to one type used by all individuals. Vocal learning is also employed during vocal development in ontogenesis, together with maturation. The existence of social groups in other species together with the lack of research suggest that traditions are more widespread among cetaceans than is currently known.
... They also emit non-signature whistles, such as shared whistles between affiliated individuals, that are often produced when traveling together [16][17][18]. Whistles serve a variety of communicative functions including individual identification [6,19], maintaining group cohesion [16], information sharing [19,20], and expressing distress [21][22][23][24]. For fission-fusion societies, like those of delphinids, acoustic communication is imperative for group cohesion in occluded waters, mother-calf bonding, social memory, and maintaining relationships [16,20,[25][26][27]. ...
... Whistles serve a variety of communicative functions including individual identification [6,19], maintaining group cohesion [16], information sharing [19,20], and expressing distress [21][22][23][24]. For fission-fusion societies, like those of delphinids, acoustic communication is imperative for group cohesion in occluded waters, mother-calf bonding, social memory, and maintaining relationships [16,20,[25][26][27]. To be successful, the animal must be able to hear and be heard in a noisy ocean environment. ...
... Whistles also had to be greater than 0.25 s in duration to be counted, which excluded brief tonal sounds described as "chirps" [7,19,67]. Whistle rates were then calculated as number of whistles per min (i.e., duration of the noise event in min) per dolphin (i.e., 20). ...
Bottlenose dolphins (Tursiops truncatus) rely on frequency-and amplitude-modulated whistles to communicate, and noise exposure can inhibit the success of acoustic communication through masking or causing behavioral changes in the animal. At the US Navy Marine Mammal Program (MMP) in San Diego, CA, dolphins are housed in netted enclosures in the San Diego Bay and exposed to noise from vessels, unmanned underwater vehicles, and other remote sensing devices. The acoustic behavior of 20 dolphins was monitored and whistle rates during noise events were quantified. Whistle rates during the onset of the event (i.e., the first 5 min) did not significantly differ from the pre-onset (5 min immediately preceding). Whistle rates were also not significantly different for the entire duration of the event compared to a matched control period. The noise's frequency range (i.e., control, mid-frequency (0-20 kHz) or high-frequency (21-80 kHz)), signal-to-noise ratio, and sound pressure level were not significantly related to the dolphins' whistle rate. Considering this is a location of frequent and moderate noise output, these results lend support to established guidelines on anthropogenic noise exposure for cetaceans, suggesting that moderate noise exposure levels may not impact communication efforts in bottlenose dolphins.
... These whistle types are primarily used to maintain contact with [33,39] and address [42] one another. Bottlenose dolphins have been shown to increase the production rate of signature whistles during isolation [24,43] or separation [39,44], with shifts in structural characteristics, such as frequency and duration, providing a vocal cue of the underlying arousal state of an individual [24,43,45,46]. Pulsed sounds emitted by bottlenose dolphins include echolocation used to orient and locate objects such as prey [38] and burst pulsed sounds, which are likely a graded signal with contextdependent functions used in social interactions [47,48]. ...
... These whistle types are primarily used to maintain contact with [33,39] and address [42] one another. Bottlenose dolphins have been shown to increase the production rate of signature whistles during isolation [24,43] or separation [39,44], with shifts in structural characteristics, such as frequency and duration, providing a vocal cue of the underlying arousal state of an individual [24,43,45,46]. Pulsed sounds emitted by bottlenose dolphins include echolocation used to orient and locate objects such as prey [38] and burst pulsed sounds, which are likely a graded signal with contextdependent functions used in social interactions [47,48]. ...
... Time-frequency spectrograms of the acoustic recordings (FFT = 1024, frequency range = 0-40 kHz, time series window = 10 s, Hann window, 50% overlap) were analysed in Adobe Audition CC (v 6.0; Adobe Inc., San Jose, CA, USA). Signature whistles are often produced when animals are separated from the group [43] and temporary separation can be used to determine signature whistles of individuals [33,34]. A signature whistle catalogue was generated from temporary separation sessions recorded with simultaneous vocal notes in 2016, whereby each animal was placed in a separate pool for 10-20 min. ...
Emotions in animals may be expressed by arousal and understanding this often relies upon the monitoring of their behaviour. Under human care, animals' arousal states may be linked to husbandry decisions, whereby animals may display arousal responses to scheduled events such as feeding and human interaction. Here, we investigate vocal correlates of arousal associated with public presentations of bottlenose dolphins (Tursiops spp.) in human care by comparing vocal production rates and characteristics between high and low arousal contexts. Elevated arousal during the day compared with overnight was characterised by increased signature and non-signature whistle production. High intensity broadband crack vocalisations were produced less than whistles during the day and did not correlate with increased arousal around presentation times. Three of ten dolphins increased signature whistle production before and/or after presentation sessions, indicating elevated arousal and variation in individual responses. Many individuals elevated minimum frequency and suppressed maximum frequency of signature whistles in a way that correlated with higher arousal contexts, indicating that these may therefore be good indicators of changes in arousal state. Overall, our study demonstrates that passive acoustic monitoring can provide a useful indication of arousal linked to husbandry decisions, and that individual variation in vocal responses, likely linked to personality, is important to consider.
... Toothed whales produce a diverse range of sounds employed in prey detection, navigation, and communication with conspecifics (Caldwell et al., 1990;Janik and Slater, 1998). Many dolphin species emit narrowband, frequency-modulated tonal sounds known as whistles, which serve in maintaining contact and social communication (Caldwell et al., 1990). ...
... Toothed whales produce a diverse range of sounds employed in prey detection, navigation, and communication with conspecifics (Caldwell et al., 1990;Janik and Slater, 1998). Many dolphin species emit narrowband, frequency-modulated tonal sounds known as whistles, which serve in maintaining contact and social communication (Caldwell et al., 1990). The structure and functions of these calls differ within and between dolphin species, influenced by factors such as group size, behavioral activity, body size, and phylogenetic relatedness (Janik and Slater, 1998;Lammers et al., 2003;Cook et al., 2004;May-Collado and Wartzok, 2008). ...
... The structure and functions of these calls differ within and between dolphin species, influenced by factors such as group size, behavioral activity, body size, and phylogenetic relatedness (Janik and Slater, 1998;Lammers et al., 2003;Cook et al., 2004;May-Collado and Wartzok, 2008). Signature whistles, the most commonly produced type by bottlenose dolphins (Tursiops truncatus), are individually distinct in their frequency modulation pattern and convey information about individual identity (Caldwell and Caldwell, 1965;Caldwell et al., 1990). They have been found to be the predominant whistle type emitted when bottlenose dolphins are isolated (Caldwell and Caldwell, 1965), serve as contact calls during intraspecific communication , and underwater contact maintenance when dispersed (Janik and Slater, 1998). ...
Acoustic signals play a crucial role in communication among animals, particularly in dolphins. Signature whistles, one of their most extensively studied vocalizations, enable dolphins to convey their identity to conspecifics through individually distinct whistle contours. However, it remains unclear whether rough-toothed dolphins (Steno bredanensis) also produce signature whistles with individually identifying contours and, if so, whether they are associated with stress and poor health, such as in bottlenose dolphins. To bridge this knowledge gap, we recorded sounds emitted by a live-stranded rough-toothed dolphin during its rehabilitation in May 2017 at Isla Mujeres, Quintana Roo, Mexico. We assessed if the dolphin produced a signature whistle and whether whistle rate, inter-whistle interval, mean low and high frequencies, and blood chemistry measures, changed significantly over time. While isolated from conspecifics during rehabilitation, the dolphin generated a single, repeated, and stereotyped whistle contour that met the previously established SIGnature IDentification criteria for signature whistle emissions for bottlenose dolphins. Whistle characteristics varied over the 11 recording days: whistle rate and inter-whistle interval significantly decreased over time; the number of whistles with preceding echolocation click trains decreased over time; and mean low and high frequencies changed over recording days. We conclude that this rough-toothed dolphin possessed what resembles a signature whistle contour, and the emission of this contour underwent significant changes throughout the rehabilitation process. While our study presents evidence of a single rough-toothed dolphin producing a signature whistle, further research is necessary to determine whether this vocal behavior is prevalent across the species.
... Dolphins have a diverse repertoire of communicative signals. Among the most studied are narrowband and frequencymodulated tonal sounds called whistles, that can be classified into signature and non-signature whistles based on their function and pattern of emission (Caldwell et al., 1990;Janik and Sayigh, 2013). Signature whistles are stereotypic sounds that encode information about individual identity and, thus, are used as contact calls (Caldwell et al., 1990), whereas non-signature whistles are non-stereotypic sounds produced in a wide range of social contexts (Sayigh et al., 1990;Macfarlane et al., 2017;2017Rachinas-Lopes et al., 2017. ...
... Among the most studied are narrowband and frequencymodulated tonal sounds called whistles, that can be classified into signature and non-signature whistles based on their function and pattern of emission (Caldwell et al., 1990;Janik and Sayigh, 2013). Signature whistles are stereotypic sounds that encode information about individual identity and, thus, are used as contact calls (Caldwell et al., 1990), whereas non-signature whistles are non-stereotypic sounds produced in a wide range of social contexts (Sayigh et al., 1990;Macfarlane et al., 2017;2017Rachinas-Lopes et al., 2017. However, most studies of the impact of anthropogenic noise on dolphin whistles do not take into account whistle function, and limit descriptions to overall changes in frequency, contour complexity, and temporal characteristics (Morisaka et al., 2005a;May-Collado & Wartzok 2008;Perez-Ortega et al., 2021). ...
... This result is also supported by the whistle repertoire analysis (see Section 5.3). Changes in whistle modulation, could indicate a change in dolphin behavioral activities and levels of alertness during the lockdown (Caldwell et al., 1990;Janik et al., 1994;Sayigh et al., 1995;Esch et al., 2009;Corrias et al., 2021). Kassamali-Fox et al. (2019) found that dolphins in Dolphin Bay are less likely to stay socializing and foraging in the presence of tour boats, and tend to increase avoidance behaviors (i.e., traveling) as an effect of tour boat presence. ...
Underwater noise from human activities is recognized as a world-wide problem, with important repercussions on the acoustic communication of aquatic mammals. During the COVID-19 pandemic, the government of Panama went into a nationwide lockdown to limit the spread of the virus. This lockdown resulted in the closing of tourism infrastructure and limited mobility in both land and coastal areas. We used this “natural experiment” as an opportunity to study the impact of tour-boat activities on dolphin communication by using passive acoustic monitoring data collected before and during the lockdown at Dolphin Bay, Bocas del Toro, Panama. During the lockdown, tour-boat activity was absent, but boats transporting people and supplies were allowed to circulate. The shift in type of boat activity within the lockdown resulted in lower ambient noise levels and more frequent detections of dolphin sounds. We also detected a more diverse whistle repertoire during the lockdown than in the pre-lockdown period, even when accounting for variation in sample coverage. A Random Forest Analysis classified whistles between the two periods with high accuracy (92.4% accuracy, κ = 0.85) based primarily on whistle modulation and duration. During the lockdown, whistles were longer in duration and less modulated than pre-lockdown. Our study shows that a shift in boat traffic activity can generate significant changes in dolphin habitat, and in their communicative signals, an important consideration given ongoing unregulated ecotourism in the region.
... Those used for communication include click-based "burst-pulse" sounds and narrow-band tonal whistles. The best studied of these sounds are signature whistles, which were first described by Melba and David Caldwell in the 1960's (Caldwell and Caldwell, 1965, and see a more thorough description in Caldwell et al., 1990). They found that isolated dolphins primarily produced stereotyped whistle contours (patterns of frequency change over time) that were unique to each individual. ...
... A 'whistle type' is defined as all whistles visually categorized as sharing a particular frequency modulation pattern (Sayigh et al., 2007;Kriesell et al., 2014); here we use the term 'signature whistle type' to describe a whistle type that has been identified as a signature whistle of a specific individual dolphin. Examples of several signature whistle types are shown in Figure 2. One of the most distinctive aspects of many bottlenose dolphin signature whistles is the presence of often-repetitive elements, called "loops" by the Caldwells (Caldwell et al., 1990). Whistles that consist of just a single, non-repeated element are referred to as "single-loop" whistles ( Figure 2A). ...
... However, there are examples of whistles changing over time, some in subtle ways, and others more dramatic (see examples in Figure 9). We also observed rare examples of individuals apparently producing two different signature whistles in the same recording session (i.e., both were produced in approximately equal amounts), a phenomenon described by Caldwell and Caldwell (1968) for a common dolphin (Delphinus delphis) and by Caldwell et al. (1990) for 2 of the 120 bottlenose dolphins in their sample. ...
Common bottlenose dolphins (Tursiops truncatus) produce individually distinctive signature whistles that are learned early in life and that help animals recognize and maintain contact with conspecifics. Signature whistles are the predominant whistle type produced when animals are isolated from conspecifics. Health assessments of dolphins in Sarasota, Florida (USA) provide a unique opportunity to record signature whistles, as dolphins are briefly separated from conspecifics. Recordings were first made in the mid 1970’s, and then nearly annually since 1984. The Sarasota Dolphin Whistle Database (SDWD) now contains 926 recording sessions of 293 individual dolphins, most of known age, sex, and matrilineal relatedness. The longest time span over which an individual has been recorded is 43 years, and 85 individuals have been recorded over a decade or more. Here we describe insights about signature whistle structure revealed by this unique and expansive dataset. Signature whistles of different dolphins show great variety in their fundamental frequency contours. Signature whistle types (with ‘whistle type’ defined as all whistles visually categorized as sharing a particular frequency modulation pattern) can consist of a single stereotyped element, or loop (single-loop whistles), or of multiple stereotyped loops with or without gaps (multi-loop whistles). Multi-loop signature whistle types can also show extensive variation in both number and contour of loops. In addition, fundamental frequency contours of all signature whistle types can be truncated (deletions) or embellished (additions), and other features are also occasionally incorporated. However, even with these variable features, signature whistle types tend to be highly stereotyped and easily distinguishable due to the extensive variability in contours among individuals. In an effort to quantify this individual distinctiveness, and to compare it to other species, we calculated Beecher’s Information Statistic and found it to be higher than for any other animal signal studied so far. Thus, signature whistles have an unusually high capacity to convey information on individual identity. We briefly review the large range of research projects that the SDWD has enabled thus far, and look ahead to its potential to answer a broad suite of questions about dolphin communication.
... Сигналы взрослых дельфинов модифицируются на протяжении всей жизни под воздействием множества факторов, поэтому представляет интерес изучение сигналов новорожденных дельфинов с оригинальными акустическими характеристиками [3]. Наибольшее количество работ на сегодняшний день посвящено изучению частотно-модулированных (ЧМ) сигналов дельфинов, известных как свисты [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] и др. Однако реги-страция этих сигналов производилась в основном только в полосе частот до 22 кГц или меньше. ...
... У изученных представителей семейства дельфинов (Delphinidae) взрослые особи используют свисты для поддержания сплоченности и координации действий между собой и группами дельфинов, рассредоточенными в пространстве на расстояниях до 10-12 км [5,[8][9][10]. Каждый дельфин имеет собственный отличительный свист, с уникальной для каждой особи формой частотного контура, играющий индивидуально опознавательную роль, так называемый "автограф". ...
... Каждый дельфин имеет собственный отличительный свист, с уникальной для каждой особи формой частотного контура, играющий индивидуально опознавательную роль, так называемый "автограф". Форма частотного контура "свиста-автографа" воспроизводится дельфином с сохранением легко узнаваемого паттерна с небольшими изменениями и является доминирующей в индивидуальном репертуаре звуков особи (до 90%), что подтверждается большим количеством работ [5,[9][10][11][12][13] и др. Есть также свисты с вариабельным контуром, фрагментарные свисты и другие, роль которых пока не ясна [14]. ...
Известно, что неонатальные дельфины начинают издавать ЧМ-сигналы (свисты) сразу после рождения. Цель нашей работы – изучение динамики параметров ЧМ-сигналов новорожденной в первые дни ее жизни. Акустические сигналы новорожденной самки дельфина афалины (Tursiops truncatus) и ее родителей были записаны с помощью двухканальной системы в полосе частот 0.1–220 кГц с дина-
мическим диапазоном 81 дБ, через 22, 46, 46.5 и 47 ч после рождения. ЧМ-сигналы сопоставлены с дельфинами, измерены и проанализированы параметры сигналов, особенности их динамики и распределения значений. Показано, что новорожденная периодически продуцирует серии ЧМ-сигналов путем перебора их частотных контуров и значений параметров в случайном порядке без повторений. При этом большинство параметров ЧМ-сигналов имеют квазинормальное распределение значений, поэтому более 90% сигналов не имеют экстремальных (максимальных и минимальных) значений соответствующих параметров. Рассмотренные механизмы формирования ЧМ-сигналов новорожденной, вероятно, играют ключевую роль в оптимизации развития и тестирования совместной работы органов и систем их генерации, рецепции и слуховой обработки в раннем постнатальном онтогенезе.
... The consistent frequency-time pattern of signature whistles has been shown to serve as an identifier for which dolphin is whistling, even when other voice features were removed (Janik et al., 2006;Sayigh et al., 2017). Signature whistles can have repeated elements of the same frequency pattern which were termed loops (Caldwell et al., 1990). Sometimes, there were differences between the first and last loops (i.e., introductory and terminal loops) of a signature whistle compared to the middle loops (Caldwell et al., 1990). ...
... Signature whistles can have repeated elements of the same frequency pattern which were termed loops (Caldwell et al., 1990). Sometimes, there were differences between the first and last loops (i.e., introductory and terminal loops) of a signature whistle compared to the middle loops (Caldwell et al., 1990). While the altered terminal loop may be used as a cue that a caller is finished with their turn, not all signature whistles have a distinctive final loop, or even multiple loops (Caldwell et al., 1990). ...
... Sometimes, there were differences between the first and last loops (i.e., introductory and terminal loops) of a signature whistle compared to the middle loops (Caldwell et al., 1990). While the altered terminal loop may be used as a cue that a caller is finished with their turn, not all signature whistles have a distinctive final loop, or even multiple loops (Caldwell et al., 1990). Therefore, there are likely other cues that allowed for such tight temporal spacing during antiphonal calling bouts. ...
Bottlenose dolphins have individually distinct signature whistles that are characterized by a stereotyped frequency-time contour. Signature whistles are commonly exchanged with short time delays between calls. Dolphin whistles are produced by pressurized nasal sacs that increase and then decrease in pressure over emission. This study found that the relative amplitude modulation pattern over time exhibited the same fade-in and then fade-out pattern in the signature whistles of eight bottlenose dolphins at the Navy in San Diego, CA. Both the initial and final five percent of the whistle’s duration also had significantly lower mean relative amplitude than the center five percent. The current analyses of the amplitude-time relationship was then integrated to a previously reported model of the negative relationship between relative log amplitude and log peak frequency. This produced a more robust model for accounting for the predictable aspects of the more broadly non-stereotyped amplitude modulations of signature whistles. Whether dolphins can intentionally manipulate these amplitude features or they are simple by-products of the sound production system, and further whether they are perceived and utilized by receivers, is an exciting area for continued research.
... Bottlenose dolphins produce a wide variety of vocalizations as part of a rich acoustic repertoire that are broadly classified as clicks, whistles, and burst pulse sounds (Jones et al. 2020). Both whistles and burst pulses have been suggested to be prevalent in social contexts (Overstrom 1983;Caldwell et al. 1990;dos Santos et al. 1990;Herzing 1996;Jones and Sayigh 2002;Blomqvist and Amundin 2004;Díaz López and Shirai 2010;Vollmer et al. 2015). Whistle production has been most commonly related to maintaining group cohesion, coordination of group feeding behaviour and in situations where animal identification may be important, such as periods of isolation or during mother-calf communication (e.g. ...
... Whistle production has been most commonly related to maintaining group cohesion, coordination of group feeding behaviour and in situations where animal identification may be important, such as periods of isolation or during mother-calf communication (e.g. Caldwell et al. 1990;Herzing 1996;Janik and Slater 1998;Díaz López and Shirai 2010;Jones et al. 2020). The production of burst pulses, a much less studied type of vocalization in wild populations, predominates in social and feeding contexts and is associated with different levels of arousal, aggression, foraging events and/or mate acquisition alliances (Overstrom 1983;dos Santos et al 1990dos Santos et al , 1995Connor and Smolker 1996;Herzing 2000;Janik 2000;Blomqvist and Amundin 2004;Díaz López and Shirai 2010;Vollmer et al. 2015;King et al. 2019). ...
... Unlike burst-pulsed sounds, the emission of whistles does not seem to show any relationship with the composition of the dyad or with the period of the year in which they are produced. This type of frequency-modulated sounds are considered contact calls and have a function rather linked to the coordination and cohesion of the group (Caldwell et al. 1990;Janik 2009;Díaz López 2011;Jones et al. 2020). Whistles are strongly linked to other variables such as the number of individuals, identity, behaviour, long-distance communication, and the presence of calves. ...
A fundamental question in animal behaviour is the role of vocal communication in the regulation of social interactions in species that organise themselves into social groups. Context dependence and seasonality in vocalizations are present in the communication of many species, although very little research has addressed this dependence in marine mammals. The study presented here examined variations in the rate at which free-ranging dyads of bottlenose dolphins emit social-signals in an effort to better understand the relationship between vocal communication and social context. The results demonstrate that changes in the social-signal production in bottlenose dolphins are related to the sex of the partner, mating season and social affiliation between the components of the dyad. In a context of foraging behaviour on the same feeding ground, mixed (male-female) dyads were found to emit more pulsed burst sounds during the mating season. Another relevant aspect of the study seems to be the greater production of agonistic social-signals in the dyads formed by individuals with a lower degree of social affiliation. Overall, this study confirms a clear relationship between dyad composition and context-specific social-signals that could reflect the motivational state of individuals linked to seasonal changes in vocal behaviour.
... They produce echolocation clicks to navigate and locate food (Au, 1993), and social sounds such as whistles, calls, screams, barks, pops, and quacks when communicating with each other (Jones et al., 2020). Among the latter sounds, whistles are the most studied (e.g., Caldwell et al., 1990;Janik, 2009). These whistles are narrow banded, and frequency modulated and can be further categorized into "variants" or "signature" whistles based on their function and pattern of emission (Caldwell et al., 1990). ...
... Among the latter sounds, whistles are the most studied (e.g., Caldwell et al., 1990;Janik, 2009). These whistles are narrow banded, and frequency modulated and can be further categorized into "variants" or "signature" whistles based on their function and pattern of emission (Caldwell et al., 1990). Variant whistles are nonstereotypic sounds produced in a wide range of social contexts, often at a greater frequency than signature whistles (Sayigh et al., 1990;Rachinas-Lopes et al., 2017). ...
... Variant whistles are nonstereotypic sounds produced in a wide range of social contexts, often at a greater frequency than signature whistles (Sayigh et al., 1990;Rachinas-Lopes et al., 2017). In contrast, signature whistles are stereotypic sounds that encode information about individual identity and thus are used as contact calls (Caldwell et al., 1990). Signature whistles facilitate group cohesion (Janik and Slater, 1998;Janik, 2009), development and maintenance of male-male alliances (King et al., 2019), in communication between mother and calf pairs (Smolker et al., 1993); and they are also used as a greeting signal when dolphins groups meet in the wild (Quick and Janik, 2012). ...
The complete collection of papers from the research topic "Whale-watching impacts: science, human dimensions and management"
... The study of these whistles has been integral in the field of communication, has set the stage for incredible advancements in our understanding of marine mammal acoustics, and has been one of the most explored signals for comparison with human language evolution. While the frequency-time contour of signature whistles has been extensively studied (e.g., Caldwell and Caldwell, 1965;Caldwell et al., 1990;Janik et al., 2006;Janik and Sayigh, 2013;Sayigh et al. 2007), we know very little about the amplitude modulation pattern across these stereotyped emissions. Nikol'skii (2012) suggested that mammal vocalizations were typically driven by frequency modulation patterns or amplitude modulation patterns, but not both. ...
... Here we assess the relative amplitude contours of signature whistles. These distinctive whistle contours have been long established to be driven by a stereotyped frequency modulation pattern (Caldwell and Caldwell, 1965;Caldwell et al. 1990). There is currently a dearth of knowledge as to whether the amplitude distribution is stereotyped or variable across signature whistles. ...
... It was still interesting that more energy was focused in the relatively lower frequency bands compared to higher frequencies. Caldwell et al. (1990) also found that the lower frequencies of the whistles they analyzed contained more energy than the higher frequency components of the whistle. There are a couple of possible explanations for this. ...
Bottlenose dolphin signature whistles are characterized by distinctive frequency modulation over time. The stable frequency contours of these whistles broadcast individual identity information. Little is known however, about whether or not the amplitude contour is also stereotyped. Here, we examined the relative amplitude-time contour of signature whistle emissions from eight bottlenose dolphins (Tursiops truncatus) in the U.S. Navy Marine Mammal Program (MMP) in San Diego, CA. The results suggested that unlike the stable frequency-time contour, the amplitude-time contour of signature whistles were largely non-stereotyped, characterized by large variability across multiple whistle emissions. Relative amplitude was negatively related to log peak frequency, with more energy focused in the lower frequency bands. This trend was consistent over all eight dolphins despite having quite different signature whistle contours. This relationship led to the amplitude contours being slightly more stereotyped within than between dolphins. We propose that amplitude across signature whistle emissions may serve as an avenue for encoding additional communicative information. We encourage future studies to incorporate analyses of amplitude contours in addition to frequency contours of signature whistles in order to begin to understand what role it may play in the dolphin communication system.
... This type of whistle was first described in common bottlenose dolphins, Tursiops truncatus (Caldwell & Caldwell, 1965). It is defined as whistles with a frequency contour unique to an individual that is the predominant call produced when isolated (Caldwell et al., 1990;Janik & Slater, 1998;Sayigh et al., 2007). In bottlenose dolphins, SWs are learned during the first year of life (Caldwell & Caldwell, 1979;Fripp et al., 2005;Sayigh et al., 1990) and remain stable for long periods Sayigh et al., 1990). ...
... However, these signals are also produced during group meetings for cohesion (Janik & Slater, 1998;Quick & Janik, 2012), mother and calf contact (Kuczaj et al., 2015;Smolker et al., 1993) and maintaining weaker social bonds with conspecifics that individuals spend less time with (Chereskin et al., 2022). SWs represent approximately 38%e70% of whistle production in unrestrained swimming bottlenose dolphins (Buckstaff, 2004;Cook et al., 2004;Watwood et al., 2005), but can reach 100% for isolated individuals in captivity (Caldwell et al., 1990). The number of SWs is also higher during captureerelease events than when animals are free (Esch et al., 2009). ...
Dolphin communication involves acoustic signals, including whistles, and the well-studied bottlenose dolphins produce individually distinctive whistles called signature whistles (SWs). The production of a potential SW by an injured Indo-Pacific humpback dolphin has been reported, but no study has attempted to validate this finding in this species. Using data collected during encounters with free-ranging Indo-Pacific humpback dolphins at two locations in the northern South China Sea, we investigated the production of SWs by these dolphins. Of the 3846 analysed whistles, 37% were identified as potential SWs (PSWs) using the SIGnature whistle IDentification method and categorized into 82 PSW types. Overall, PSWs were identified during 54% of encounters. Given the high production rate of stereotyped whistles (62% of all whistles in 90% of encounters) compared with the identified PSWs, we suggest that the SIGnature whistle IDentification method criteria cannot be fully adapted for the detection of SWs in Indo-Pacific humpback dolphins, and more research should be conducted to adapt the criteria to the species. In addition, the characteristics of PSWs differed slightly between locations, potentially because of the geographical separation of populations and habitat differences (e.g. noise levels). The present results confirm the production of stereotyped whistles, including PSWs, by Indo-Pacific humpback dolphins. Further research should be conducted to confirm whether these whistles are similar to bottlenose dolphins’ SWs.
... Nevertheless, dolphins can modify the frequency range of their SWs to prevent interference in noisy environments (18,19). Although each SW is predominantly vocalized by the owner, dolphins may also emit the SW of their conspecifics (vocal matching) (20)(21)(22)(23)(24). SWs represent a significant portion of the vocalization repertoire (38-70%) in the wild (25), and about 90% in isolation (25)(26)(27). Therefore, it was suggested that SWs act as "names" that can be used to transmit a dolphin's identity or call conspecifics out of sight (vocal labeling). ...
... It is important to note that the nodes indicate the whistle sub-categories without information about the identity of the dolphin that emitted the whistles. However, SWs dominate the acoustic vocalizations of dolphins both in the wild and in captivity, representing between 50 and 90% of their whistle repertoire (25)(26)(27). In our entire dataset, the SWs represented 91.3% of the total number of extracted whistles. ...
Bottlenose dolphins exhibit a sophisticated social structure, known as a fission-fusion society. To sustain this complex system, dolphins rely on a rich vocal repertoire: clicks exclusively used for echolocation, burst-pulse sounds associated with emotions during social interactions, and whistles, including signature whistles that serve as individual-specific identifiers (names).
How dolphins maintain their complex social structure based only on a limited repertoire of sounds remains elusive. Previous studies suggest that contextual information can be transferred by the modulation of the whistles.
Here, we investigated the whistle variability using a comprehensive computational approach, and studied the structure of the interactions between the whistle variants. Using a unique large dataset, acquired in a natural environment, we observed that signature whistles exhibit variations in their frequency contours. Unsupervised clustering revealed that signature whistles could be classified into sub-categories (signature whistle variants). The existence of these categories, and their independence on the emitter dolphin, indicate that these variations are not random. Analysis of pairwise interactions between sub-categories revealed a clustered structure similar to that of their social hierarchy. Network analysis of this structure showed that whistle sub-categories had different functional roles: some acted as hubs, others as bridges, and certain were used for turn-taking between the main whistle categories. We also found that the dolphins emit signature whistles of their deceased mothers, a phenomenon only observed in human language.
... A striking example of signals with a pronounced individually specific structure is signature whistles of bottlenose dolphins Tursiops truncatus [15]. These signals have a unique frequency modulation pattern for each individual (a "frequency contour" observed on the spectrogram), which plays a key role in individual identification of dolphins [17,34,61,66]. It is believed that these signature whistles serve for communication and coordination between group members, and their proportion can reach more than 90% of all signals produced by a dolphin [17,35,77]. ...
... These signals have a unique frequency modulation pattern for each individual (a "frequency contour" observed on the spectrogram), which plays a key role in individual identification of dolphins [17,34,61,66]. It is believed that these signature whistles serve for communication and coordination between group members, and their proportion can reach more than 90% of all signals produced by a dolphin [17,35,77]. Signature whistles are formed during the first year of an individual's life, gradually acquiring a frequency contour stereotypy (i.e., stable frequency-time parameters) [16], after which they can remain unchanged for 12-25 years [39,60]. ...
... Individual recognition mechanisms have played a key role in odontocete ecology. However, information about SW derives mostly, from the common bottlenose dolphins (Tursiops truncatus; Bruck et al., 2022;Caldwell & Caldwell, 1965;Caldwell et al., 1990;Gridley et al., 2014;Rio et al., 2022). In addition to bottlenose dolphins, individually distinctive SW have been identified and described for eight other delphinid species (Rio, 2023a), namely: Indo-Pacific bottlenose dolphins (Tursiops aduncus; Gridley et al., 2014), spinner dolphins (Stenella longirostris; Rio, 2023a), common dolphins (Delphinus delphis; Caldwell & Caldwell, 1968;Fearey et al., 2019), Atlantic spotted dolphins (Stenella frontalis; Caldwell & Caldwell, 1970), Pacific white-sided dolphins (Sagmatias obliquidens; Caldwell et al., 1973) Knowledge about SW remains limited primarily due to the challenges in assessing certain cetacean species. ...
... Occasionally, false killer whales were observed accelerating and jumping out of the water, during the (e.g., environmental, social, behavioral, genetic, or cultural aspects) can increase acoustic emission rates and, consequently, SW production and rates (May-Collado & Wartzok, 2008;Quick & Janik, 2008). When dolphins are isolated from their conspecifics, for example, the SW rate in their acoustic repertoire can reach up to 100% (Caldwell et al., 1990;Janik & Slater, 1998;Sayigh et al., 2007). ...
... Therefore, one of the primary goals of marine monitoring is the collection, storage, analysis, and interpretation of underwater bioacoustic signals [6][7][8] . Specifically, the identification of spatial and temporal patterns in these acoustic signals could help characterize certain dolphin living conditions [9][10][11] . This applies in general, but especially to the description of the depredation event, in order to document the presence of dolphins in the vicinity of nets and increase knowledge of dolphin predation behavior near fishing gear. ...
... The acoustic repertoire of common bottlenose dolphins is characterized by a high degree of complexity 10,11 , including vocal learning, i.e., the ability to tune and produce new vocalizations through experience, and vocal mimicry, i.e., the ability to imitate sound patterns 12 . This species typically emits three main types of acoustic signals: frequency-modulated whistles, echolocation clicks, and multiple burst pulse signals. ...
Globally, interactions between fishing activities and dolphins are cause for concern due to their negative effects on both mammals and fishermen. The recording of acoustic emissions could aid in detecting the presence of dolphins in close proximity to fishing gear, elucidating their behavior, and guiding potential management measures designed to limit this harmful phenomenon. This data descriptor presents a dataset of acoustic recordings (WAV files) collected during interactions between common bottlenose dolphins (Tursiops truncatus) and fishing activities in the Adriatic Sea. This dataset is distinguished by the high complexity of its repertoire, which includes various different typologies of dolphin emission. Specifically, a group of free-ranging dolphins was found to emit frequency-modulated whistles, echolocation clicks, and burst pulse signals, including feeding buzzes. An analysis of signal quality based on the signal-to-noise ratio was conducted to validate the dataset. The signal digital files and corresponding features make this dataset suitable for studying dolphin behavior in order to gain a deeper understanding of their communication and interaction with fishing gear (trawl).
... These vocalizations are developed during animals' first months of life, through a vocal production learning process based on their auditory social experiences; moreover, they are issued in a repetitive pattern capable of transmitting senders' identity to their surroundings. Whistle copies of SWs, eventually produced by conspecifics, are rare and can be recognizable as such because copiers consistently modify some acoustic parameters of a signal when copying it (Caldwell et al. 1990;Esch et al. 2009;Fripp et al. 2005;Harley 2008;Heiler et al. 2016;Janik 1999Janik , 2009Janik and Slater 1998;Janik et al. 2006;Jones et al. 2020b;King et al. 2013;Kriesell et al. 2014;Longden et al. 2020;Luís et al. 2016;Papale et al. 2015;Rio et al. 2022;Sayigh et al. 1995Sayigh et al. , 2007Sayigh et al. , 2017Terranova et al. 2021;Watwood et al. 2005). ...
... Although SWs are the best example of a designed individual acoustic label within the animal kingdom (Sayigh et al. 2007), scientific knowledge about their function and use is mostly documented in bottlenose dolphins (Tursiops truncatus) (Caldwell et al. 1990;Cones et al. 2022;Gridley et al. 2014;. Their use and presence in other delphinid taxa remain poorly investigated and understood (Cones et al. 2022;Fearey et al. 2019). ...
A dolphin’s signature whistle (SW) is a distinctive acoustic signal, issued in a bout pattern of unique frequency modulation contours; it allows individuals belonging to a given group to recognize each other and, consequently, to maintain contact and cohesion. The current study is the first scientific evidence that spinner dolphins (Stenella longirostris) produce SWs. Acoustic data were recorded at a shallow rest bay called “Biboca”, in Fernando de Noronha Archipelago, Brazil. In total, 1902 whistles were analyzed; 40% (753/1,902) of them were classified as stereotyped whistles (STW). Based on the SIGID method, 63% (472/753) of all STWs were identified as SWs; subsequently, they were categorized into one of 18 SW types. SWs accounted for 25% (472/1,902) of the acoustic repertoire. External observers have shown near perfect agreement to classify whistles into the adopted SW categorization. Most acoustic and temporal variables measured for SWs showed mean values similar to those recorded in other studies with spinner dolphins, whose authors did not differentiate SWs from non-SWs. Principal component analysis has explained 78% of total SW variance, and it emphasized the relevance of shape/contour and frequency variables to SW variance. This scientific discovery helps improving bioacoustics knowledge about the investigated species. Future studies to be conducted in Fernando de Noronha Archipelago should focus on continuous investigations about SW development and use by S. longirostris, expanding individuals’ identifications (Photo ID and SW Noronha Catalog), assessing long-term whistle stability and emission rates, and making mother–offspring comparisons with sex-based differences.
... A repeated contour, or multiloop whistle, is either connected with no breaks in the entire whistle contour or disconnected with a maximum inter-loop-interval of 0.25 s (Esch et al. 2009), which is common for T. aduncus . Although the frequency modulation of the overall whistle remains remarkably stable (see Sayigh et al. 2007;Luís et al. 2016), structural components of each constituent loop may differ based on the order of production within the whistle, i.e. introductory (first), central (middle) and terminal (end) loops (Caldwell et al. 1990;Sayigh et al. 1990). Additionally, bottlenose dolphins may produce whistles with a greater number of loops as they mature (Caldwell et al. 1990). ...
... Although the frequency modulation of the overall whistle remains remarkably stable (see Sayigh et al. 2007;Luís et al. 2016), structural components of each constituent loop may differ based on the order of production within the whistle, i.e. introductory (first), central (middle) and terminal (end) loops (Caldwell et al. 1990;Sayigh et al. 1990). Additionally, bottlenose dolphins may produce whistles with a greater number of loops as they mature (Caldwell et al. 1990). ...
Individually distinctive signature whistles are used by common bottlenose dolphins (Tursiops truncatus) during social interactions and to facilitate group cohesion. There is evidence from a few populations that Indian Ocean bottlenose dolphins (T. aduncus) also use signature whistles. We investigated this from a coastal resident population of T. aduncus in Mozambique. Video-audio data were collected during recreational swim-with activities over 12 years, where potential signature whistles were identified from 28 individuals. Of the 405 whistles documented, 75% were produced in SIGID bouts. Visual assessment of individual signature whistle contours demonstrated temporal stability for up to 8 years. Overall, most signature whistle types had upsweep frequency modulation and were emitted as multiloop whistles. Comparing all whistle contours to each other indicated low discrimination between individuals, with contours frequently categorised together. However, sex differences in the frequency characteristics of whistles were identified, with females whistling at lower frequencies than males. Our results indicate either a shared whistle repertoire or identity encoding with subtle contour features, requiring acute auditory perception and discrimination to decipher caller identity. More widespread geographic investigation into signature whistle use may demonstrate variation in acoustic communication systems for bottlenose dolphins, which are thus far not well understood.
... Not much is known about the functionality of chirps. However, in captivity, chirps seemed to be produced more often when dolphins were positively reinforced [49]. Even though the function of LFN sounds is still unclear, they have been associated with socializing and heightened emotional contexts [50]. ...
... Interestingly, the presence of nocturnal vocalizations can further confirm that these areas are equally frequented by dolphins during night and daytime. The nocturnal occurrence of all vocalizations including whistles, chirps, LFN sounds, BP sounds, and echolocation clicks also suggests similar behavioral interactions, with special reference to social interactions [46,[49][50][51]. ...
Describing the acoustic repertoire of cetaceans is necessary to understand the functionality of their sounds and the effect anthropogenic pressures have on animals living in a marine environment. This study provides a description of the acoustic repertoire of bottlenose dolphins (Tursiops truncatus) in the Cres-Lošinj archipelago based on continuous 24-h recordings collected from two monitoring stations, both inside and outside the Natura 2000 Site of Community Importance, during an 8-day period in March/April 2020 and a 13-day period in July/August 2020. A total of 1008 h were visually and aurally analyzed to identify vocalizations and investigate diel and seasonal patterns in their parameters. Furthermore, sound pressure levels were calculated for the low (63 Hz–2 kHz) and high (2 kHz–20 kHz) frequency range. Bottlenose dolphins in the Cres-Lošinj archipelago were found to produce whistles, chirps, low frequency narrow-band sounds, burst pulse sounds, and echolocation clicks showing that dolphins are present at both monitoring stations, during both diel and seasonal periods, in a comparable manner. This paper also provides evidence that whistles, chirps, and low frequency narrow-band sounds change their parameters in relation to the background noise in the area, that varies according to diel and seasonal patterns. This suggests a vocal plasticity in the species and a coping strategy to avoid masking of relevant acoustic signals for the local population in the Cres-Lošinj archipelago.
... Nowadays, it is known that signature whistles (SWs) are frequency-modulated vocalizations that remain stable Although SWs are the best example of a designed individual acoustic label within the animal kingdom (Sayigh et al. 2007), scienti c knowledge about their function and use is mostly documented in bottlenose dolphins (Tursiops truncatus) (Caldwell et al. 1990; Cones et al. 2022; Gridley et al. 2014;. Their use and presence in other delphinid taxa remain poorly investigated and understood (Cones et al. 2022;Fearey et al. 2019). ...
... SW frequency parameters observed for Atlantic spotted dolphins often ranged from 4 kHz to 18 kHz, and the duration of whistle bouts ranged from 0.5 to 8 s(Herzing, 1996). SW fundamental frequency recorded for bottlenose dolphins ranged from 4 kHz to 20 kHz, at duration ranging from 0.1 to 3.6 s(Caldwell et al., 1990).Whistle contour plays central role in signature information, i.e., individual recognition,(Janik et al. 2006; Kershenbaum et al. 2013;Sayigh et al. 2007); its variations based on aspects, such as frequencies and duration, may convey additional information, such as animals' emotional state(Norris et al., 1985;Steiner, 1981;Wang et al., 1995). Humans are endowed with great ability to recognize complex visual patterns, which enabled testing the reliability of the classi cation carried out by the author of this publication (RR) and by external observers who did not have previous experience with bioacoustics studies, based on the comparison between contours of SW the types and copies. ...
Signature whistle (SW) is a distinctive acoustic signal, issued in a bout pattern of unique frequency modulation contour; it allows individuals belonging to a given group to recognize each other and, consequently, to maintain contact and cohesion. The current study is the first scientific evidence that spinner dolphins ( Stenella longirostris ) produce SWs. Acoustic data were recorded at a shallow rest bay called “Biboca”, in Fernando de Noronha Archipelago, Brazil. In total, 1,902 whistles were analyzed; 37.85% (720/1,902) of them were classified as stereotyped whistles (STW). Based on the SIGID method, 60.97% (439/720) of all STWs were identified as SWs; subsequently, they were categorized into one of 18 SW types. SWs accounted for 23.08% (439/1,902) of the acoustic repertoire. External observers have shown perfect agreement at the time to classify whistles into the adopted SW categorization. Most acoustic and temporal variables measured for SWs showed mean values similar to those recorded in other studies with spinner dolphins, whose authors did not differentiate SWs from non-SWs. Principal component analysis has explained 77.79% of total SW variance, and it emphasized the relevance of shape/contour and frequency variables to SW variance. This scientific discovery helps improving bioacoustics knowledge about the investigated species. Future studies should focus on continuous investigations about SW development and use by Stenella longirostris to help expanding individuals’ identification (Photo ID and SW Noronha Catalog), assessing long-term stability and emission rates, and making mother-offspring comparisons (sex-based differences).
... The acoustic plasticity of dolphins [4] is revealed by their ability to imitate the vocalizations of conspecifics [5], to modify signals in relation to environmental and anthropogenic noise [4,6], and to emit different signals in relation to different behaviors [7]. Delphinids, the family where the interpretation of acoustic signals has been studied most extensively, produce a variety of sounds that can be classified into two main categories: rapid repetition rate echolocation clicks, click trains, burst, and tonal frequency modulated whistles [8][9][10]. According to some studies, whistles and burst pulses are predominant in social contexts [9,11]. ...
... Delphinids, the family where the interpretation of acoustic signals has been studied most extensively, produce a variety of sounds that can be classified into two main categories: rapid repetition rate echolocation clicks, click trains, burst, and tonal frequency modulated whistles [8][9][10]. According to some studies, whistles and burst pulses are predominant in social contexts [9,11]. Alterations in whistle parameters may indicate high variation in the message conveyed and reflect changes in the transmission of emotional information [12]. ...
Marine mammal vocal elements have been investigated for decades to assess whether they correlate with stress levels or stress indicators. Due to their acoustic plasticity, the interpretation of dolphins’ acoustic signals of has been studied most extensively. This work describes the acoustic parameters detected in whistle spectral contours, collected using passive acoustic monitoring (PAM), in a bycatch event that involved three Bottlenose dolphins during midwater commercial trawling. The results indicate a total number of 23 upsweep whistles recorded during the bycatch event, that were analyzed based on the acoustic parameters as follows: (Median; 25th percentile; 75th percentile) Dr (second), total duration (1.09; 0.88; 1.24); fmin (HZ), minimum frequency (5836.4; 5635.3; 5967.1); fmax (HZ), maximum frequency, (11,610 ± 11,293; 11,810); fc (HZ), central frequency; (8665.2; 8492.9; 8982.8); BW (HZ), bandwidth (5836.4; 5635.3; 5967.1); Step, number of step (5; 4; 6). Furthermore, our data show that vocal production during the capture event was characterized by an undescribed to date combination of two signals, an ascending whistle (upsweep), and a pulsed signal that we called “low-frequency signal” in the frequency band between 4.5 and 7 kHz. This capture event reveals a novel aspect of T. truncatus acoustic communication, it confirms their acoustic plasticity, and suggests that states of discomfort are conveyed through their acoustic repertoire.
... Lima et al. (2017) reported that burst pulses and whistles were sometimes produced during solitary play in captive bottlenose dolphins. In captivity, whistles (especially signature whistles) are frequently produced by isolated individuals (Caldwell et al. 1990), but in these situations their role is obviously to restore the contact with other animals. ...
... Dolphins are an indicator species, common to the British Isles, with the status and health of regional populations acting as important metrics for conservation and in assessing ecosystem health 8,9 . Acoustically they emit a diverse range of signals, employed in hunting, navigation, and communication, consisting of highly directional transient signals (echolocation clicks) and tonal omni-directional, frequency modulated whistles 10,11 . The presence of these acoustic cues within broadband acoustic recordings can be used as a proxy for true animal presence 12 , but manual extraction of signals is laborious and unrealistic on an appropriate timescale for conservation. ...
... Fifteen years of observational study led to the discovery that Japanese tits emit a unique alarm call that elicits an antipredator response specific to the presence of snakes (Suzuki, 2018). Long-term studies of bottlenose dolphins have shown that each animal produces its own individually distinctive signature whistle that is learned early in life and helps animals recognize and maintain contact with conspecifics (Caldwell & Caldwell, 1965;Caldwell et al., 1990). These efforts were successful because they included carefully curated data collection gained over a long period, and their scientific relevance was augmented by the depth of multimodal knowledge gleaned throughout the course of each study. ...
... In odontocetes, the acoustic activity of mothers before and after parturition has been investigated in common bottlenose dolphins (Tursiops truncatus) and belugas (Delphinapterus leucas). Common bottlenose dolphins use individually distinct "signature whistles" (Caldwell and Caldwell 1965;Caldwell et al. 1990) to maintain contact with conspecifics (Janik and Slater 1998) in their extensive social networks (Connor et al. 2000). Signature whistles are also used to facilitate mother-calf reunions after separation (Sayigh et al. 1990;Smolker et al. 1993;Tyack and Sayigh 1997;Mello and Amundin 2005;King et al. 2013). ...
Active acoustic emission from a mother to a calf after parturition is one strategy used to enhance recognition of mothers by calves and develop, then maintain, a mother–calf bond from an early stage. This study predicted that a high-calling postpartum period exists in a social delphinid, the Pacific white-sided dolphin (Lagenorhynchus obliquidens). This species produces pulsed call sequences for vocal exchange with conspecifics, and these sequences appear to be an important signal between mothers and calves. Sounds were recorded from three pregnant females at the Niigata City Aquarium, Marinepia Nihonkai, Japan, before and after each birth in 2019, 2020, and 2021 to investigate the rate of their pulsed call sequences. Continuous data from prior to four days to five days following parturition, opportunistic data within the last pre-parturition month, and data from the postpartum period were obtained from the females. The pulsed call sequence gradually increased during the last gestational month. A high-rate sequence was repeated daily for four days pre-parturition and faded within several hours postpartum, and few sequences were produced from the day after parturition. Contrary to our prediction, the many pre-parturition sequences and fewer postpartum sequences suggest a low efficiency of postpartum imprinting in this species.
... Whistles are frequency and amplitude-modulated narrowband vocalizations that sound tonal to the human ear (e.g., [22,23]). Bottlenose dolphins develop and maintain individually distinctive whistle contours (i.e., patterns of frequency modulation over time) that are termed signature whistles (e.g., [22,24,25]). Signature whistles are most commonly emitted during periods spent isolated from conspecifics and are produced at an abnormally high repetition rate during periods of distress (e.g., [26][27][28][29][30]). ...
(1) Background: When a human or animal is recovering from general anesthesia, their medical team uses several behavioral and physiological parameters to assess their emergence from the unconscious state to complete wakefulness. However, the return of auditory and acoustic behaviors indicative of the complete return of consciousness in humans can be difficult to assess in a completely aquatic non-human mammal. Dolphins produce sound using the nasal system while using both passive auditory and active biological sonar (echolocation) to navigate and interrogate their environment. The sounds generated by dolphins, such as whistles and clicks, however, can be difficult to hear when the animal is submerged. (2) Methods: We implemented a system to audibly and visually (i.e., using spectrograms) monitor the underwater acoustic behavior of dolphins recovering from anesthesia. (3) Results: Eleven of the twelve recorded dolphins began echolocating within 92 min (Mean = 00:43:41 HH:MM:SS) following spontaneous respirations. In all cases, the dolphins echolocated prior to whistling (Mean = 04:57:47). The return of echolocation was significantly correlated to the return of the righting reflex (Mean = 1:13:44), a commonly used behavioral indicator of dolphin emergence. (4) Conclusions: We suggest that acoustic monitoring for the onset of click production may be a useful supplement to the established medical and behavioral biomarkers of restoring consciousness following anesthesia in bottlenose dolphins.
... The first studies based on the quantitative and qualitative analyses of the repertoire of D. delphis emerged in the 1990s (Moore and Ridgway, 1995;Oswald 2003;Ansmann et al., 2007;Petrella et al., 2012;Papale et al., 2014;Azzolin et al., 2021;Pagliani et al., 2022). The common dolphin presents a varied repertoire of whistles and some features are possible signature whistles (Ansmann et al., 2007;Petrella et al., 2012;Fearey et al., 2019) that may transmit individual identities (Caldwell et al., 1990). ...
Animal vocalizations have nonlinear characteristics responsible for features such as subharmonics, frequency jumps, biphonation, and deterministic chaos. This study describes the whistle repertoire of a short-beaked common dolphin (Delphinus delphis) group at Brazilian coast and quantifies the nonlinear features of these whistles. Dolphins were recorded for a total of 67 min around Cabo Frio, Brazil. We identify 10 basic categories of whistle, with 75 different types, classified according to their contour shape. Most (45) of these 75 types had not been reported previously for the species. The duration of the whistles ranged from 0.04 to 3.67 s, with frequencies of 3.05-29.75 kHz. Overall, the whistle repertoire presented here has one of the widest frequency ranges and greatest level of frequency modulation recorded in any study of D. delphis. All the nonlinear features sought during the study were confirmed, with at least one feature occurring in 38.4% of the whistles. The frequency jump was the most common feature (29.75% of the whistles) and the nonlinear time series analyses confirmed the deterministic chaos in the chaotic-like segments. These results indicate that nonlinearities are a relevant characteristic of these whistles, and that are important in acoustic communication.
... Pulsed sounds include echolocation clicks and communicative burst pulse sounds, which are trains of short pulses with a high pulse repetition rate (up to several hundred pulses per second) sounding like 'creaks ', 'squeaks', 'buzzes', 'barks', 'screams', etc., to the human ear (Herman & Tavolga, 1980). Specific vocalizations used to broadcast the caller's identity were first discovered for bottlenose dolphins Tursiops truncatus by M. Caldwell and D. Caldwell (Caldwell et al., 1990;Caldwell & Caldwell, 1965), who noticed that dolphins, when isolated from others, tended to produce stereotyped repeated whistles with an individually unique frequency modulation pattern (contour), which were termed 'signature whistles'. Subsequent studies (see review Janik & Sayigh, 2013) have confirmed that these calls serve for individual identification among dolphins (Sayigh et al., 1999) and function as contact calls (Janik & Slater, 1998;Watwood et al., 2005). ...
Social toothed whales are known to produce specific vocalizations that may serve for individual or group recognition and maintaining cohesion among group members. In beluga whales Delphinapterus leucas, these vocalizations referred to as “contact calls” are relatively long duration, repeated stereotyped broadband sounds. Although these calls are thought to be critical in mother‐calf communication, they are utilized by individuals of different ages and sex. We investigated possible occurrence of contact calls in all‐male beluga groups from the White Sea, Russia. Among the vocalizations analyzed (n = 1169), a considerable proportion (58%) appeared to be potential contact calls. They were subjectively classified into 61 types of mostly complex broadband sounds combined with a narrow band element. The positive linear relationship (R² = 0.90) between the number of unique call types identified in the recordings and the number of belugas observed in the research area suggests that the calls serve as individual signatures. Belugas tended to produce these calls in a series, with the intercall intervals between the same and different call types mainly >1 s and <1 s, respectively. This suggests that vocal exchange by individually distinctive calls, like those of captive belugas and some other social species, might take place. The current study provides more insight into contact call usage in wild belugas and may serve as a basis for long‐term monitoring of their seasonal occurrence, abundance, and site fidelity, as well as for investigating their social organization.
... The sounds emitted play a fundamental role in their social interactions, individual recognition, group coordination, foraging success, and recognition of an individual's surroundings (Lind et al., 1996;Rendall et al., 1996;Janik and Slater, 1998;Azzolin et al., 2017;MacFarlane et al., 2017;La Manna et al., 2020). The acoustic repertoire of bottlenose dolphins includes echolocation clicks (broadband click trains), burst-pulsed sounds (closely spaced broadband click trains) and frequency modulated whistles (narrowband tonal sounds) (Caldwell et al., 1990;Janik, 2009;Herzing, 2014;La Manna et al., 2017;Luí s et al., 2021;Pace et al., 2022). Echolocation clicks are known to be used primarily for navigation and foraging while whistles and pulsed sounds are considered to be used for individual recognition, social maintenance, group coordination, communication, as well as foraging activity (Au, 1993;Branstetter et al., 2012;Janik et al., 2012;MacFarlane et al., 2017). ...
Bottlenose dolphins have a complex vocal repertoire that varies depending on behavioral context, social structure, group composition, and anthropogenic pressures. This current study describes the whistle characteristics of bottlenose dolphins for the first time in the South Adriatic Sea while assessing the potential differences between whistle characteristics of geographically separated dolphins within neighbouring waters of the North Ionian Sea. The results show that whistle characteristics were similar between Taranto Gulf (Italy) and Boka Bay (Montenegro), despite their spatial differences. The mean peak frequency was 10kHz for each study location while the mean minimum and maximum frequency ranged from 7 to 14kHz. The average duration of whistles was 500 milliseconds. These results share similarities with previous literature, although several studies reported slightly different mean peak frequencies, ranging up to 15kHz in the neighbouring waters of Croatia and Italy. Further, harmonics were produced and formed in 40% of the whistles in Taranto Gulf and 30% of the whistles in Boka Bay. A high incidence of harmonics has previously been associated with behavioral states (i.e., travelling) and with certain types of marine traffic (i.e., fishing vessels). Therefore, it is important to collect simultaneous data on the visual behavior of the focal group as well as document the type and density of marine traffic within the proximity of the dolphins to have an in-depth understanding of vocal behavior. Despite the similarities of whistle characteristics of Taranto and Boka Bay, the whistle contours showed notable variations. Upsweep whistles were the most regularly produced whistle type in each location, which coincides with previous studies in the Mediterranean Sea. However, the least produced whistle had a concave contour in Taranto and was flat in Boka Bay. Previous studies have confirmed that flat whistles account for the least produced whistle contour in the Mediterranean Basin. Examining the whistle characteristics and the variation in whistle contours provides an in-depth understanding of the behavioral complexity as well as its plasticity in the presence of pressure. Therefore, future studies need to include behavior, group composition, noise levels, and human presence to enable an effective understanding of variation in whistle characteristics of bottlenose dolphins.
... Belugas can also modify the acoustic properties of calls during social activities or when vessel noise is present. These have been fairly well examined (Caldwell et al., 1990;Angiel, 1996;Lesage et al., 1999;Belikov & Belkovich, 2007;Chmelnitsky & Ferguson, 2012;Garland et al., 2015). Given the general increase in humanproduced ocean noise in the Arctic and beyond (Belkovich & Shchekotov, 1992;O'Corry-Crowe, 2009;Hobbs et al., 2019), characterizing acoustic behavior is vital as we seek to estimate, mitigate, and manage noise impacts. ...
While echolocation is vital to the sensory ecology of odontocetes, we have few data characterizing the signals of most species, limiting our understanding of key attributes of these animals, especially for those with a diverse range of habitats. Beluga whales (Delphinapterus leucas) have successfully overcome the pressures of living in both shallow and deep open water habitats. We characterized the echolocation clicks of 13 wild beluga whales during temporary capture-and-release events in Bristol Bay, Alaska (USA). We extracted and examined 556 high-quality clicks from approximately 22 hours of recordings. As a group, the duration (41.1 ± 17.3 µs; mean ± SD), peak frequency (97.9 ± 34.4 kHz), centroid frequency (101.9 ± 23.9 kHz),-3 dB bandwidth (29.1 ± 14.4 kHz),-10 dB bandwidth (67.7 ± 31.8 kHz), and root mean square (RMS) bandwidth (27.8 ± 8.1 kHz) were assessed. These are the first on-axis data from wild belugas in their natural shallow water habitat within 1 m. Beluga whales emit clicks with high frequency and high source level in extremely shallow waters regardless of the potential strong reverberations and clutter. These results provide a foundation for future studies on how this species manipulates its sonar to successfully operate in acoustically challenging shallow waters.
... Bottlenose dolphins produce three types of sound. Two of the sounds are broadband, echolocation clicks and burstpulsed sounds, and the third is the whistle, a frequencymodulated narrow-band sound (Caldwell et al., 1990). Whistles are used to convey identity information (Janik et al., 2006), facilitate group cohesion (Janik and Slater, 1998;Quick and Janik, 2012), and address conspecifics (King and Janik, 2013). ...
During the COVID-19 pandemic, changes in vessel activity and associated noise have been reported globally. Sarasota Bay is home to a large and increasing number of recreational vessels as well as a long-term resident community of bottlenose dolphins, Tursiops truncatus. Data were analyzed from two hydrophones to compare the soundscape during the COVID-19 pandemic to previous years (March–May 2020 and 2018/2019). Hourly metrics were calculated: vessel passes, 95th percentile sound levels [125 Hz and 16 kHz third octave bands (TOBs), and two broader bands: 88–1122 Hz and 1781–17 959 Hz], and dolphin whistle detection to understand changes in vessel activity and the effect on wildlife. Vessel activity increased during COVID-19 restrictions by almost 80% at one site and remained the same at the other site. Of the four sound level measures, only the 125 Hz TOB and 88–1122 Hz band increased with vessel activity at both sites, suggesting that these may be appropriate measures of noise from rapid pass-bys of small vessels in very shallow (<10 m) habitats. Dolphin whistle detection decreased during COVID-19 restrictions at one site but remained the same at the site that experienced increased vessel activity. The results suggest that pandemic effects on wildlife should not be viewed as homogeneous globally.
... Bottlenose dolphins produce three types of sound. Two of the sounds are broadband, echolocation clicks and burstpulsed sounds, and the third is the whistle, a frequencymodulated narrow-band sound (Caldwell et al., 1990). Whistles are used to convey identity information (Janik et al., 2006), facilitate group cohesion (Janik and Slater, 1998;Quick and Janik, 2012), and address conspecifics (King and Janik, 2013). ...
During the COVID-19 pandemic, decreases in large vessel activity and low-frequency noise have been reported globally. Sarasota Bay is home to a large and increasing number of recreational vessels, as well as a long-term resident community of bottlenose dolphins, Tursiops truncatus. We analyzed data from two hydrophones to compare the soundscape during the COVID-19 pandemic to previous years (March–May 2020 and 2018/2019). Hourly metrics were calculated: vessel passes, 95th percentile noise levels (125 and 16 kHz Third Octave Bands (TOBs) and two broadbands: 88–1122 Hz, 1781–17959 Hz), and dolphin whistle detection, to understand changes in vessel activity and the effect on wildlife. Vessel activity increased during COVID-19 restrictions by almost 80% at one site and remained the same at the other. Changes in noise levels varied between sites. Only the 125 Hz TOB and 88–1122 Hz band increased with vessel activity at both sites, suggesting this may be an appropriate measure of noise from small vessels in very shallow (<10 m) habitats. Dolphin whistle detection decreased during COVID-19 restrictions at one site but remained the same at the site that experienced increased vessel activity. Our results suggest that pandemic effects on wildlife should not be considered to be homogeneous globally.
... Tyack (2003) reviews the history of laboratory and field studies of signature whistles and provides an excellent synthesis of the two. Laboratory studies have revealed the following: a) dolphins can imitate arbitrary non-natural sounds and can produce these sounds to label objects that have been previously associated with these sounds (Reiss & McCowan, 1993;Richards et al., 1984); b) dolphins do not inherit their signature whistles from their parents but rather develop their signature whistles by learning to imitate particular sounds present in their natal habitat (reviewed in Tyack & Sayigh, 1997); c) signature whistles of adult females are more stable over time than signature whistles of males, some of whom vocally converge on similar whistles with close male associates (Caldwell, Caldwell & Tyack, 1990); d) dolphins learn to imitate the signature whistles of other dolphins with whom they interact (Tyack, 1986); and e) -553 -an individual dolphin is more likely to produce its own signature whistle when isolated from a familiar group of dolphins than when the group remains cohesive (Janik & Slater, 1998). This latter finding suggested to Janik and Slater (1998) that signature whistles may function as contact calls between adults. ...
... rapid bursts of packets of clicks commonly used in social contexts, with an inter-click interval (ICI) of typically less than 0.004 ± 0.001) (Tyack and Clark 2000;Blomqvist and Amundin 2004;Luís et al. 2016), and frequency and amplitude modulated whistles (i.e. tonal, narrowband, frequency and amplitude modulated sounds) (Kellogg et al. 1953;Dreher 1961;Lilly and Miller 1961;Caldwell and Caldwell 1965;Caldwell et al. 1990). Dolphins drive their sound production by pressurising two nasal cavities that sit below the blowhole (Mead 1975). ...
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.
... Similarly, a bottlenose dolphin may be able to detect a whistle masked by noise, but unable to recognize the frequency contour and, thus, unable to recognize the identity of the caller. Dolphins use "signature whistles" or stereotyped whistles that uniquely identify the caller to conspecifics (Caldwell et al. 1990;Janik and Sayigh 2013). The stereotyped frequency-modulated pattern is used for recognition, while amplitude may encode other information such as emotional state (Jones et al. 2022). ...
Anthropogenic noise is an increasing threat to marine mammals that rely on sound for communication, navigation, detecting prey and predators, and finding mates. Auditory masking is one consequence of anthropogenic noise, the study of which is approached from multiple disciplines including field investigations of animal behavior, noise characterization from in-situ recordings, computational modeling of communication space, and hearing experiments conducted in the laboratory. This paper focuses on laboratory hearing experiments applying psychophysical methods, with an emphasis on the mechanisms that govern auditory masking. Topics include tone detection in simple, complex, and natural noise; mechanisms for comodulation masking release and other forms of release from masking; the role of temporal resolution in auditory masking; and energetic vs informational masking.
... During the past 60 years, different methodologies have been tested to solve the problem of identification and to investigate in depth cetacean bioacoustics. The first attempts involved isolating the focal animal through temporary captures (Lilly and Miller, 1961;Caldwell et al., 1990), but although this method increases the probability to identify callers, it implies stressful conditions and alteration of the animal's spontaneous behavior (Thomas et al., 2002). A less invasive technique associated vocal emission with the production of bubble streams (McCowan, 1995;Herzing, 1996). ...
Study of animal communication and its potential social role implies associating signals to an emitter. This has been a major limitation in the study of cetacean communication as they produce sounds underwater with no distinctive behavioral signs. Different techniques have been used to identify callers, but all proved to have ethical or practical limitations. Bio-logging technology has recently provided new hopes, but tags developed so far are costly and do not allow sufficiently reliable discrimination between calls made by the tagged individual and those made by the surrounding individuals. We propose a new device developed at reasonable cost while providing reliable recordings. We tested caller identification through recordings of vocal production of a group of captive bottlenose dolphins under controlled and spontaneous contexts. Our device proved to identify callers through visual examination of sonograms and quantitative measures of amplitudes, even if tagged emitters are 0.4 m apart (regardless of body orientations). Although this device is not able to identify emitters in an entire group when all individuals are not equipped, it enables efficient exclusion of individuals who were not the caller, suggesting that identification of a caller would be reliable if all the individuals were equipped. This is to our knowledge the first description of a promising low-cost safe recording device allowing individual identification of emitters for captive dolphins. With some improvements, this device could become an interesting tool to increase our knowledge of dolphin acoustic communication.
... Signature whistles were first identified from individuals in captivity (Caldwell et al., 1990) or during temporary restraint of wild individuals (Sayigh et al., 1990). This early work showed the high consistency in the frequency modulation patterns within individuals over time and that they typically are produced in bouts . ...
Abundance estimates of cetaceans are often acquired through capture‐recapture analysis of photographically identified individuals. An alternative method, using capture‐recapture of individually distinct signature whistles detected from acoustic underwater recording units, has recently been demonstrated. Here we investigate the effect of array configuration (1–3 hydrophones within 0.45 km2) and recording duty cycles (six variations of 33%, 50%, or 66% sampling periods) on the detection rate of dolphin signature whistles. Twenty‐one signature whistle types were identified and used to create capture histories for each hydrophone and all potential array configurations. Open population models were used to estimate capture probabilities and precision for all data sets. The effect of different duty cycles on detectability were investigated by artificially applying six duty cycles to the continuously recorded data. Results demonstrate that location is more important than redundancy in small‐scale arrays, even with detection distances as small as 750 m, and that duty cycling can increase survey durations without decreasing detectability. To acoustically sample intermittent signals of dispersed populations, it is more effective to space hydrophones further apart, in known high‐use areas. This study provides insight into the application of capture‐recapture to signature whistles, improving methods for long‐term, noninvasive monitoring of elusive delphinids.
... Bottlenose dolphins (Tursiops truncatus and Tursiops aduncus) use individually distinctive signature whistles (34,35) that are developed by animals early in life apparently by copying and then changing whistles they hear (36,37). This novel signature whistle is then used by not only the owner to broadcast its identity (38,39) but also conspecifics to address the whistle owner (32,(40)(41)(42). Approximately 38 to 70% of bottlenose dolphin whistles in the wild are signature whistles (35). ...
While studies have demonstrated concept formation in animals, only humans are known to label concepts to use them in mental simulations or predictions. To investigate whether other animals use labels comparably, we studied cross-modal, individual recognition in bottlenose dolphins (Tursiops truncatus) that use signature whistles as labels for conspecifics in their own communication. First, we tested whether dolphins could use gustatory stimuli and found that they could distinguish between water and urine samples, as well as between urine from familiar and unfamiliar individuals. Then, we paired playbacks of signature whistles of known animals with urine samples from either the same dolphin or a different, familiar animal. Dolphins investigated the presentation area longer when the acoustic and gustatory sample matched than when they mismatched. This demonstrates that dolphins recognize other individuals by gustation alone and can integrate information from acoustic and taste inputs indicating a modality independent, labeled concept for known conspecifics.
Understanding the impact of human disturbance on wildlife populations is of societal importance,1 with anthropogenic noise known to impact a range of taxa, including mammals,2 birds,3 fish,4 and invertebrates.5 While animals are known to use acoustic and other behavioral mechanisms to compensate for increasing noise at the individual level, our understanding of how noise impacts social animals working together remains limited. Here, we investigated the effect of noise on coordination between two bottlenose dolphins performing a cooperative task. We previously demonstrated that the dolphin dyad can use whistles to coordinate their behavior, working together with extreme precision.6 By equipping each dolphin with a sound-and-movement recording tag (DTAG-37) and exposing them to increasing levels of anthropogenic noise, we show that both dolphins nearly doubled their whistle durations and increased whistle amplitude in response to increasing noise. While these acoustic compensatory mechanisms are the same as those frequently used by wild cetaceans,8,9,10,11,12,13 they were insufficient to overcome the effect of noise on behavioral coordination. Indeed, cooperative task success decreased in the presence of noise, dropping from 85% during ambient noise control trials to 62.5% during the highest noise exposure. This is the first study to demonstrate in any non-human species that noise impairs communication between conspecifics performing a cooperative task. Cooperation facilitates vital functions across many taxa and our findings highlight the need to account for the impact of disturbance on functionally important group tasks in wild animal populations.
In the presence of vessels, dolphins have been found to change their habitat, behavior, group composition and whistle repertoire. The modification of the whistle parameters is generally considered to be a response to the engine noise. Little is known about the impact of the physical presence of vessels on dolphin acoustics. Whistle parameters of the coastal and oceanic ecotypes of common bottlenose dolphins in La Paz Bay, Mexico, were measured after the approach of the research vessel and its engine shutdown. Recordings of 10 min were made immediately after turning off the engine. For analysis, these recordings were divided from minute 0 to minute 5, and from minute 5:01 to minute 10. The whistles of the oceanic ecotype showed higher maximum, minimum and peak frequency in the second time interval compared to the first one. The whistle rate decreased in the second time interval. The whistles of the coastal ecotype showed no difference between the two time intervals. The physical presence of the research vessel could have induced a change in the whistle parameters of the oceanic dolphins until habituation to the vessel disturbance. The oceanic ecotype could increase the whistle rate and decrease the whistle frequencies to maintain acoustic contact more frequently and for longer distances. The coastal ecotype, showing no significant changes in the whistle parameters, could be more habituated to the presence of vessels and display a higher tolerance.
One of the most studied aspects of animal communication is the acoustic repertoire difference between populations of the same species. While numerous studies have investigated the variability of bottlenose dolphin whistles between populations, very few studies have focused on the signature whistles alone and the factors underlying differentiation of signature whistles are still poorly understood. Here we describe the signature whistles produced by six distinct geographical units of the common bottlenose dolphin (Tursiops truncatus) in the Mediterranean Sea and identify the main determinants of their variability. Particularly, the influence of the region (proxy of genetic distance), the geographic site, and the environmental (sea bottom-related) and demographical (population-related) conditions on the acoustic structure of signature whistles was evaluated. The study provides the first evidence that the genetic structure, which distinguishes the eastern and western Mediterranean bottlenose dolphin populations has no strong influence on the acoustic structure of their signature whistles, and that the geographical isolation between populations only partially affected whistle variability. The environmental conditions of the areas where the whistles developed and the demographic characteristics of the belonging populations strongly influenced signature whistles, in accordance with the "acoustic adaptation hypothesis" and the theory of signature whistle determination mediated by learning.
This study is the first baseline acoustic description of common bottlenose dolphin populations (Tursiops truncatus) from Revillagigedo Archipelago and the first identification of signature whistles (SWs) in an oceanic population of T. truncatus. A total of 85% (199/233) of the recorded whistles were classified as stereotyped whistles and subsequently (bout analysis/SIGID) categorized into one of five SW types. External observers were in perfect agreement in classifying whistles into the adopted SW categorization. SWs represented 42% (98/233) of the repertoire. Overall, most whistle types were categorized as sine (80%; SW1, SW2, SW4, and SW5) with one downsweep (20%, SW3). Roca Partida Island had the highest number of SW types. Principal component analysis explained 77% of the total SWs variance, highlighting the importance of shape/contour variables to the SWs variance. The combined mean SWs acoustic parameters from Revillagigedo Archipelago were higher than that recorded in coastal regions, which may indicate there are differences between SWs of pelagic and coastal populations. However, further acoustic and ecological studies in the Archipelago are needed to clarify and expand our findings, to identify its members (Photo ID and SW Revillagigedo Catalog), and to investigate this topic at other oceanic islands.
A description of the social structure of a species is a first step toward understanding its social organization and, ultimately, the evolutionary processes that shaped its social system. Since the mid-1960s the rapid accumulation of information from field studies of terrestrial mammals has made it possible to propose models to explain the evolution of mammalian social systems. These models have examined the species distribution of characteristics such as group size, group compositions, spatial patterns of individuals, and social interactions in relation to environmental variables (for example, Crook and Gartlan, 1966; Eisenberg et al., 1972; Clutton-Brock, 1974; Jarman, 1974; Emlen and Oring, 1977; Wrangham, 1980). Predictable patterns of organization have been found which provide insights into the adaptive significance of the social systems. Until recently, available information for cetaceans has been inadequate to allow construction of comparable models. A surge of systematic field studies of the behavior and ecology of cetaceans is beginning to provide the requisite information for examination of cetacean societies within a general mammalian context. To this end, this chapter presents the results of one study of the social structure of the bottlenose dolphin, Tursiops truncatus.
1. Sound localization was measured behaviourally for the Atlantic bottlenose porpoise (Tursiops truncatus) using a wide range of pure tone pulses as well as clicks simulating the species echolocation click. 2. Measurements of the minimum audible angle (MAA) on the horizontal plane give localization discrimination thresholds of between 2 and 3 degrees for sounds from 20 to 90 kHz and thresholds from 2-8 to 4 degrees at 6, 10 and 100 kHz. With the azimuth of the animal changed relative to the speakers the MAAs were 1-3-1-5 degrees at an azimuth of 15 degrees and about 5 degrees for an azimuth of 30 degrees. 3. MAAs to clicks were 0-7-0-8 degrees. 4. The animal was able to do almost as well in determining the position of vertical sound sources as it could for horizontal localization. 5. The data indicate that at low frequencies the animal may have been localizing by using the region around the external auditory meatus as a detector, but at frequencies about 20 kHz it is likely that the animal was detecting sounds through the lateral sides of the lower jaw. 6. Above 20 kHz, it is likely that the animal was localizing using binaural intensity cues. 7. Our data support evidence that the lower jaw is an important channel for sound detection in Tursiops.
A bottlenosed dolphin (Tursiops truncatus) was trained to mimic computer-generated "model" sounds, using a whistle mode of vocalization. Prior to training, the whistle sounds of this dolphin were limited to a few stereotyped forms, none of which resembled the model sounds. After training, high-fidelity imitations were obtained of model sounds having (a) moderately or widely swept, slow-rate frequency modulation (1-2 Hz), (b) narrowly or moderately swept frequency modulation at moderate to rapid rates (3-11 Hz), (c) square-wave frequency transitions, and (d) unmodulated (pure-tone) waveforms. New models, not heard previously, could be mimicked immediately, often with good fidelity, including mimicry of amplitude variation that had not been explicitly reinforced during training. Subsets of familiar models were mimicked with high reliability in repeated tests. In additional training, control of the mimic response was transferred from the acoustic model to objects shown the dolphin (e.g., a ball or a hoop) so that, in effect, the dolphin gave unique vocal labels to those objects. In a test of accuracy and reliability of labeling, correct vocal labels were given on 91% of 167 trials comprised of five different objects presented in random order. The dolphin's ability for vocal mimicry compared favorably with that of the more versatile mimic birds, and it contrasted sharply with the apparent lack of vocal mimicry ability in terrestrial mammals other than humans. The ability to label objects vocally was similar to abilities shown for some birds and similar, in principle, to abilities of great apes trained in visual languages to label objects through gestures or other visual symbols.
Observations of the vocal exchanges of bottlenose dolphins under various conditions are presented. Experimental conditions under which isolated emissions from each animal of a pair are separately recorded and in which the distance between the rostrum and the hydrophone is controlled are described. The exchanges consist of vocal alternations (A, then B, then A, and so on), "duets" (A plus B simultaneously), and long "solos" or "monologues." The emissions exchanged are: (i) whistles alone; (ii) slow click trains alone; (iii) simultaneous whistles and clicks from either or both animals; and (iv) squawks, quacks, blats, and so on, alone or simultaneously with whistles. Any or all of these sounds may occur in a given period. The significant carriers of meaning are to be determined. (Suggestions include various functions of relative amplitudes, absolute and relative frequency, frequency modulations, phaseshift variations, and durations of whistle emissions.) Average and peak amplitudes (at the rostrum) of each class of sound cover at least a 100-decibel range (controlled by the dolphin).
Data gathered on whistles of 126 Atlantic bottlenosed dolphins (Tursiops truncatus) of assorted sizes and both sexes indicate that the whistle varies with age in several parameters. Most, but not all, of the changes occur within the first two years of life.
An experimental study of the sonic communication signals of the dolphins Tursiops truncatus ponticus is described. The experimental animals were placed in two tanks interconnected by a two-way wideband electroacoustic line. It is shown that the dolphins use the same repertoire of sounds in two-way communications as in one-way signaling operations. It is found that the dolphin whistles have a fine structure representing bursts of short high-frequency pulses at frequencies close to the first five harmonics of the fundamental whistle tone. It is shown that the fine-structure components play a significant role in the two-way exchange of information. A physical model is postulated for the communication process on the hypothesis of a communication bridge formed by a train of partially overlapping whistles emitted by the dolphins.
Sperm whales, Physeter catodon, temporarily interrupted their own sound production in reaction to underwater pulses produced by our calibration sound sources (pingers). All seven whales that passed close to the hydrophone array at different times reacted the same way. They remained silent for at least 2 min, and some of the more distant ones quieted for shorter periods. Acoustic tracking of the sounds indicated that these whales moved underwater at a speed of about 2 knots and downward at a slope of 10–15°, in the general direction of other clicking sperm whales.
A brief comparison of intonation and tone languages is given, with criteria of the latter applied to observed whistle contours appearing in underwater recordings of Tursiops truncatus and Langenorhynchus obliquidens.
An Atlantic bottlenosed dolphin (Tursiops Truncatus) was trained to respond positively to a highly random sample of the whistles of four conspecifics and to inhibit this response when presented with a similar sample of the whistles of four other conspecifics of approximately the same age. When randomized whistles of these eight animals were presented to the subject dolphin, he responded almost 100% correctly, indicating an ability of differentiate between whistles of eight conspecifics when presented rapidly in series. (Author)
Results are presented of acoustic tests done on a juvenile male Tursiops truncatus to determine his capability for discriminating between any and all signature whistles of two other young males from the same locality. The results indicate that this discrimination is possible, regardless of the situation under which the whistle is emitted. The duration of signal (whistle) necessary for the subject's performance to be 100% correct is shown to be approximately 0.45 seconds which coincides with the duration of one complete sound loop, or single sinousoidal frequency oscillation, of a whistle emission of the animal designated as the positive stimulus in the tests. Methods of training are discussed and illustrations are presented of test whistles, along with graphs showing results of the subject's level of performance as correlated with both number of trials and duration of signal. (Author)
The available data on the sounds produced by various marine organisms are compiled, together with samples of tape recordings referenced by entry number to the descriptions and illustrations. The report is intended primarily for assistance in recognizing and identifying sounds of biological origin. Each entry includes a description of the acoustic characteristics of the sound, the identification of the source species, as far as possible, a simple line drawing of the animal, and one or more sound spectrograms taken from the recorded sample. Two classifications of the entries are given: one is based upon the acoustics characteristics of the sounds, and the other is based upon the zoological relationships of the animals. Reference is made to NAVTRADEVCEN 1212-1 and other publications for background material. (Author)
A total of 1580 whistles emitted by five spotted dolphins, Stenella plagiodon, from Florida were analyzed. Of these, 97.3% were classified as being the signature whistle of the individual studied. Statistics are included indicating a positive correlation between degree of variance from the mode in number of loops in the whistles and their variability in one other parameter; i.e., absence of the normal terminus for an individual dolphin's modal whistle. Although members of this species are regarded as having signature whistles, it was concluded that their whistles have fewer or less distinct differences between individuals and more minor variations within the whistles of one individual than do those of the Atlantic bottlenosed dolphin, Tursiops truncatus. (Author)
IN 1953, Essapian1 suggested that individual bottle-nosed
dolphins, Tursiops truncatus (Montagu), may have distinctive notes which
each dolphin can recognize. From his context, in using the word `notes'
Essapian referred to the whistle component of Tursiops phonation.
Characteristic sounds in the sonic range made by captive dolphins, or porpoises, were heard and recorded using underwater listening gear. The phonations described include those elicited by strange objects, those which accompany feeding activity, a distinctive sound heard during the mating season, and others less clearly associated with particular circumstances or stimuli. T. truncatus is highly vocal, a characteristic which may apparently be related to certain behavioral traits and to its usual coastal or inshore environment. On the other hand, only two types of phonation have definitely been attributed to S. plagiodon, an offshore species whose behavior differs in many respects from that of Tursiops. Previous accounts of popoise sounds and the circumstances attending their production are reviewed.
The whistle vocalizations of two bottlenosed dolphins, Tursiops truncatus, were recorded at the Sealand Aquarium in Brewster, Massachusetts. The identification of which dolphin within the group produced a vocalization was made possible by a telemetry device attached to the dolphin's head with a suction cup. 77% of the identified whistles (219 our of 284) fell into two primary categories, type 1 and type 2 (Table 1). The remaining 23% of whistles fell into five secondary categories. Of the primary whistles produced by one dolphin, 78% were of type 1 (22% type 2), while 69% of primary whistles from the other dolphin were of type 2 (31% type 1). The result that each of the dolphins favored a different primary whistle supports the findings of Caldwell and Caldwell (1965), that each dolphin produces an individually distinctive whistle. But in the present study, both dolphins produced both primary whistle types. This may represent mimicry of signature whistles.
The baleen whales differ from the toothed whales and dolphins in life history and in social organization. Even though they grow to a larger size, young baleen whales tend to develop more rapidly than dolphins and toothed whales. Except for the mother-calf bond, most groups of baleen whales are short-lived, lasting only for hours, and individual-specific associations appear to be exceptions to the norm. Most toothed whales live in more structured groups, in which young animals have a long period of dependency and social learning. The communication signals described for different cetacean species have functions suited to the interactions that predominate in their societies.
A small telemetry device, called a "vocalight," was designed for attachment to a dolphin's head using a suction cup. The vocalight lights up a variable number of light-emitting diodes depending upon the loudness of sounds received at a hydrophone within the suction cup. If vocalights matched for sensitivity are put on each dolphin within a captive group, observers can identify which dolphin produces a vocalization. Use of vocalights indicates that source levels of whistles from captive bottlenosed dolphins, Tursiops truncatus, range from approximately 125 to over 140 dB re: 1 microPa at 1 m.
Pure-tone whistles (2403) by four individual dolphins (Delphinus delphis bairdi) were analyzed for duration and the elapse of time before either response by another animal or a repeat whistle by the same
animal. Only five major types of whistle emissions were recorded, all stereotyped and each characteristic of the animal emitting
it. Only one of the four animals emitted two different whistles, one of which was rare and both of which were stereotyped.
A pure-tone chirp and pulsed sounds are discussed. We found no evidence of a dolphin "language," but we present evidence of
social response to acoustic signals.
Two isolated dolphins (Tursiops truncatus) were provided with an electronic acoustic link during alternate periods of approximately
2 minutes. The dolphins repeatedly communicated in a tight sequence when the acoustic link was connected. Their responses
varied as the experiment progressed. Some information regarding possible meaning of the whistles was obtained.
The sonic emissions of the bottlenose dolphin are remarkably complex. Three classes of these sounds are discussed and presented graphically. The sine-type wave whistles range in frequency from about 4000 to 18,000 cycles per second. The clicks contain components of this same frequency range plus some components of higher frequencies. Complex waves of high amplitude and of many frequencies are also emitted in water or in air. Situations in which sounds of one or more of these classes can be elicited simultaneously from one and from two restrained animals are described. The necessity for, and occurrence of, creakings for purpose of navigation, ranging, and recognition (sonar) have been eliminated in the experiments under discussion.
Analysis of the many different vocal productions of pairs of bottlenose dolphins (Tursiops truncatus Montagu) and the related behavior patterns shows that one pair of specific short (0.2 to 0.6 second) whistles was consistently stimulated by physical distress. This call stimulated nearby animals to push the head of the distressed
animal to the surface to breathe. After the animal breathed, a vocal exchange preceded other forms of aid.
Etiology of the chirp sounds emitted by the Atlantic bottlenosed dophin: A controversial issue
- Caldwell
Statistical analysis of the signature whistle of an Atlantic bottlenosed dolphin with correlations between vocal changes and level of arousal
- M C Caldwell
- D K Caldwell
- R H Turner
Cetacean communication
- Dreher
Dolphin vocal mimicry and vocal object labeling
- Richards
Use of a telemetry device to identify which dolphin produces a sound: When bottlenosed dolphins are interacting, they mimic each other's signature whistles
- Tyack
Man/dolphin communication
- D W Batteau
- P R Markey
The dolphin observed
- Caldwell
Intraspecific transfer of information via the pulsed sound in captive odontocete cetaceans
- Caldwell
Vocalization among marine mammals
- Evans
Sound production by the Atlantic bottlenosed dolphin Tursiops truncatus
- Hollien
Bibliography of echolocation papers on aquatic mammals published between 1966 and 1978
- Nachtigall
Behavioral interactions between porpoises and sharks
- F G Wood
- Jr
- D K Caldwell
- M C Caldwell
Étude des signaux acoustiques associés a des situations de détresse chez certains cétacés odontocètes
- Busnel
Senses and communication
- Caldwell
A quantitative description of two-way acoustic communication between captive Atlantic bottlenosed dolphins (Tursiops truncatus)
- S L Gish
Periodicity of vocal activity of captive Atlantic bottlenose dolphins: Tursiops truncatus
- Powell
A preliminary investigation of the ability of an Atlantic bottlenosed dolphin to localize underwater sound sources
- M C Caldwell
- N R Hall
- D K Caldwell
- H I Hall
Underwater sounds of cetaceans
- Schevill