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Bottlenose dolphins that forage with artisanal fishermen whistle differently
Abstract
Acoustic communication is a taxonomically widespread phenomenon, crucial for social animals. We evaluate social sounds from bottlenose dolphins (Tursiops truncatus) of Laguna, southern Brazil, whose social structure is organized around a cooperative for- aging tactic with artisanal fishermen. This tactic involves stereotyped and coordinated behaviour by dolphins and fishermen and is performed by a subset of the dolphin population, splitting it into two distinct social communities. We compared the acoustic parameters and type of whistles emitted by dolphins of the “non-cooperative” and “cooperative” communities, both during their interactions with fishermen and in times where dolphins were engaged in other types of foraging. Our findings show how dol- phins’ social sounds differ between foraging tactics and social communities. The fre- quencies of six whistle types (ascending, descending, concave, convex, multiple, flat) were significantly dependent on tactics and communities. Ascending whistles were more common than expected during foraging without fishermen, and among dolphins of the non-cooperative community. Whistle acoustic parameters (duration, number of inclination changes and inflection points, and initial, final, maximum, minimum fre- quencies) also varied between social communities. In general, whistles emitted by co- operative dolphins, mainly when not interacting with fishermen, tended to be shorter, had higher frequency and more inflections than those emitted by non-cooperative dolphins. These results suggest that different whistles may convey specific informa- tion among dolphins related to foraging, which we hypothesize promote social cohe- sion among members of the same social community. These differences in acoustic repertoires add a new dimension of complexity to this unique human–animal interaction.
... Both fishers and dolphins seems to benefit from this interaction via an increase in their catch (Simões-Lopes, F abian & Menegheti, 1998). For the dolphin population, this interaction has several implications, influencing spatial (Cantor, Simões-Lopes & Daura-Jorge, 2018) and social behaviour (Daura-Jorge et al., 2012), population parameters (Bezamat et al., 2018) and acoustic behaviour; individuals who frequently interact with fishers whistle differently from those who tend to forage independently, suggesting a functional role of sounds in the development and execution of this foraging tactic (Romeu et al., 2017). ...
... To minimize the inclusion of sounds from individuals not belonging to the focal group, we only collected data when no other dolphin was sighted within the area defined by the 200 m distance between the limit of the 'cooperative zone' and the limit of the 'influence zone' (Romeu et al., 2017). Therefore, when other dolphins were observed outside the 'cooperative zone' but within the 'influence zone', the recordings were discarded. ...
... For bottlenose dolphins, whistles can be heard and recorded at distances greater than 1 km (Quintana-Rizzo et al., 2006). However, a previous study in the area (Romeu et al., 2017) and our pilot study showed that whistles emitted at distances greater than 250 m from the hydrophones are attenuated, likely due to the geography of the area, reducing the quality of the recordings. For analysis, therefore, we only included whistles not masked by other simultaneous sounds and with a good signal-to-noise ratio Romeu et al., 2017). ...
Acoustic behaviour is a key component of specialized foraging tactics for many aquatic species, especially cetaceans. However, in recent decades the natural environment has been increasingly exposed to a variety of anthropogenic noise sources, with the potential to impact natural foraging specializations dependent on acoustic communication. Here we evaluated whether boat noise has the potential to impact a rare foraging tactic used by individuals from a small population of the vulnerable Lahille’s bottlenose dolphin (Tursiops truncatus gephyreus) specialized in cooperation with artisanal fishers in southern Brazil. We tested whether the presence of boats changed the acoustic behaviour of dolphins when engaged in this cooperative foraging. We found that whistles and echolocation click rates were lower when boats were present, suggesting that cooperative foraging may potentially be reduced or interrupted by the presence of boats. Whistle parameters changed in response to the number, type and speed of boats, indicating a behavioural change and acoustic masking. Locally, our results reinforce the need for boat traffic regulations to minimize their impacts on these endangered dolphins and their rare cooperative tactic. From a broad perspective, we demonstrate how nonlethal impacts such as vessel disturbance can manifest subtle changes in animals’ natural behaviour and, in this case, present an insidious threat to a unique foraging specialization.
... For bottlenose dolphins foraging can be a cooperative behaviour (Rossbach, 1999) and feeding strategies often involve remarkable behavioural flexibility (Whitehead and Rendell, 2014). These include the division of labour with role specialisation (Gazda et al., 2005), the adoption of specialised foraging tactics, and variations in acoustic behaviour (Romeu et al., 2017). For example, bottlenose dolphins in Scotland produce a unique feeding signal during certain times of the year, apparently to recruit more dolphins to aid the hunting effort (Janik, 2000). ...
... For example, bottlenose dolphins in Scotland produce a unique feeding signal during certain times of the year, apparently to recruit more dolphins to aid the hunting effort (Janik, 2000). Romeu et al. (2017) also found differences in the time and frequency parameters of whistles emitted by dolphins of the Laguna coastline (southern Brazil) depending on foraging tactics and the social community to which the dolphins belong, suggesting that whistles may convey specific information among dolphins in relation to foraging. More generally, frequency and time variations in whistle parameters are related to behavioural context, group social structure, and calf presence (Janich et al., 1994;Hiley et al., 2016;Hawkins and Gartside, 2010;Papale et al., 2015;La Manna et al., 2019). ...
... The whistles emitted while feeding behind trawlers may differ from whistles produced during natural and not opportunistic foraging (Weir, 2010;Romeu et al., 2017), but extensive efforts on this topic are still needed. In this study we compare dolphin whistles produced during foraging in interaction with trawlers to whistles produced during foraging in the presence and absence of other motor boats, as boat noise is known to modify dolphin whistles (La Manna et al., 2013Manna et al., , 2019Manna et al., , 2020. ...
Sounds are particularly important for animals that live in complex social communities. In this study, we assessed the communication calls (whistles) that common bottlenose dolphins emit during their foraging activities in the absence and presence of motor boats and during dolphin depredation on trawlers, in Alghero (Sardinia, Italy) and Cres-Lošinj Archipelago (Croatia). The latter behaviour involves foraging on concentrated food sources during very noisy human activity and may require the emission of distinctive whistles. Thus, we investigated if whistle structure, in terms of frequency and time parameters, changes depending on these three foraging contexts. In Sardinia, during foraging in interaction with trawlers, whistles differed from those emitted during the other foraging contexts. Conversely, in Cres-Lošinj, significant variations in whistles were found to be related mainly to the presence of motor boats. This study represents the first report on how two dolphin populations adopt different acoustic tactics in the context of similar foraging behaviour. By investigating the effects of opportunistic foraging on acoustic repertoires, we provide new findings on the acoustic adaptation of dolphins to local conditions and contribute to understanding the relationships between dolphins and human activities, such as fishing and boat traffic.
https://authors.elsevier.com/a/1c7oZ1LenMKOXf
... Drawing on on-site observations and sound recording data, ethnologists have widely documented the emotional experiences of odontocetes. According to these data, delphinids, have thus developed different vocal signals, such as barks, clicks and quacks, for communication (Janik & Slater, 1998;May-Collado, 2010;Quintana-Rizzo et al., 2006;Romeu et al., 2017). Although humans can identify the differences between these sounds, their meanings cannot be interpreted through a framework built on human language. ...
... Second, undersea animal soundscapes are shaped by social and collective forces. A group of dolphins uses different types of whistles as they are travelling, socializing or foraging (Papale et al., 2017;Romeu et al., 2017;Van Parijs and Corkeron, 2001). In fission-fusion societies (e.g. ...
... In fission-fusion societies (e.g. dolphin society), whistles can be used as social sounds to facilitate social interactions, such as individual recognition and group cohesion (Quick & Janik, 2012;Romeu et al., 2017). Group foraging, for example, requires group members to use social sounds for the purpose of social co-ordination. ...
This paper examines the controversy around marine animal management in Taiwan Strait, where the sea has been territorialized by offshore wind power developers. Concerns have been focused on the impacts of pile-driving noise on the Taiwanese white dolphin which is on the IUCN list of extremely endangered species. To deal with the problem, both state and developers have been involved in volumetric practices which attempt to render the marine mammals knowable, and in turn, governable. While recent work on volumetric thinking has revealed that power is exercised through volume, we contend that insufficient attention has been given to those lively 'non-human' subjects living in the volumetric spaces. Inspired by recent scholarship on animal atmospheres and the wet ontologies, we argue that marine animals are sentient beings that cannot be known, or mapped, by the state-corporate volumetric practices which are mainly based on scientific experiments, conducted in isolated social contexts. To illustrate this, we draw on assemblage thinking and develop the idea of marine animal soundscapes. We suggest that marine animal soundscapes exist only through the embodied experience of a sensory, marine animal body, which is able to affect, and learn to be affected by, others, through non-linguistic 'signs', such as sound. We maintain that animal soundscapes are shaped by social, ecological and material circumstances, of which, the materialities of the sea, such as its liquidity, rapidity and fluidity, are of great importance. With an emphasis on the subaquatic animal soundscapes, our approach intends to extend social relationality to non-humans and calls for an ontology, distinct from the one with which existing volumetric analysts work.
... Bottlenose dolphins (Tursiops sp.) in the wild have been recoded to cooperate to capture food or to gain and maintain access to mating partners. A wide range of ingenious cooperative hunting tactics have been observed with bottlenose dolphins in the wild such as mud ring feeding (Ramos et al., 2022), strand-feeding (Jimeńez and Alava, 2015), cooperative prey herding (Benoit-Bird and Au, 2009), coordinated leader-wall hunting (Gazda et al., 2005) and even inter-specific cooperation with fishermen (Romeu et al., 2017). The diversity and flexibility of these strategies likely contributed to the successful, wide range distribution of bottlenose dolphins. ...
Cognitive enrichments have gained popularity in the past two decades in both farm animal and zoological settings. In this study, we present a cognitive enrichment device that, for the first time, allowed testing for prosocial food-sharing actions in dolphins. The device was made of a PVC tube and two caps with rope handles; one handle was fixed to the poolside whereas the other was available for the dolphins. Its internal structure kept five fish in place while maintaining a closed status. The dolphin who pulled the rope handle could not access the fish but allowed another individual to access it. Once the handle was released, however, the device closed back. The device was tested with a male and a female group, separately. The males obtained approximately a third, while the females acquired none of the fish using the device. Moreover, the males were observed to open the device more frequently and longer in the presence of their group members and with consistent roles. These results provide the first support of male dolphins’ willingness to engage in food-sharing that could be considered as an altruistic action. It also provides basis for further investigations on more detailed and long-term monitoring of the emergence and consequences of such cooperative actions.
... This type of vocalization is longer than 100 milliseconds and is emitted in frequencies varying between 0.8 and 38 kHz [14][15][16][17]. Whistles can be catalogued by visually inspecting the spectrograms and shape of the whistle contour [16,[18][19][20]. Despite difficulties in classifying whistles ternational conventions (Bern, Bonn, CITES, ACCOBAMS). ...
Recent years have seen a notable rise in dolphin-watching boat activities along the Algarve coast in Portugal, potentially affecting the common dolphin (Delphinus delphis) and bottlenose dolphin (Tursiops truncatus) local populations. This study examines the impact of increasing underwater noise levels from these boats on dolphin vocalizations. Field recordings were conducted from June to September 2022, analyzing dolphin whistles in various boat presence scenarios. The results indicate significant changes in whistle-frequency characteristics with boat presence, including increased start, low, and high frequencies, alongside a decrease in the number of inflection points in modulated whistles. The changes might negatively impact dolphin populations viability, underscoring the need for further research. Additionally, improved mitigation strategies may be necessary to reduce the potential negative effects of dolphin watching on cetacean communication and behavior in the Algarve region.
... 110-113). The ones who do sound different from the ones who don't (Romeau 2017). When not foraging, the two groups don't socialise. ...
... In Laguna, these dolphins interact positively with artisanal fishermen (cooperative fishery; Simões-Lopes, 1991;Simões-Lopes et al., 1998) at specific sites in the lagoon system where they live (Daura-Jorge et al., 2013). Some dolphins interact more frequently (known as cooperative dolphins) than others (noncooperative dolphins), and such individual variation defines their home ranges (Cantor et al., 2018) and other ecological and biological aspects, such as acoustic behavior and population characteristics Romeu et al., 2017). ...
Some dolphin species produce signature whistles, which may allow the identification of individual dolphins using passive acoustic monitoring (PAM). Identifying individuals by their sounds may enhance the opportunities for monitoring and addressing biological and ecological questions about these species. Here, we explored the potential of signature whistles to investigate ecological aspects of a resident bottlenose dolphin population. Using a limited data set, with few individuals recognized by signature whistles, combined with spatial capture‐recapture (SCR) methods, we investigated how effective such approach is describing spatial use patterns and estimating density for this population. The data were collected using 4–6 stationary bottom‐moored recorders. Since only eight signature whistles were identified, our density estimate may represent a subset of the entire population. However, even with only a few signature whistles identified, our results confirmed the center of the core area used by these dolphins as the area with the highest encounter probability. In addition, our results provided evidence that these dolphins have the same spatial use pattern at night as during the day. This study shows that SCR analysis of signature whistle data can improve our ecological knowledge and understanding of dolphin populations.
... Cooperative foraging behavior is most likely culturally transmitted in dolphins (Simões-Lopes et al., 2016). In Laguna, Brazil, the social network of bottlenose dolphins is structured by their cooperation with artisanal fishers: there are different social communities of cooperative and noncooperative dolphins within the same population (Daura-Jorge et al., 2012), which have distinct vocal communication (Romeu et al., 2017) and home ranges (Cantor et al., 2018). Honeyguides adapt at least behaviorally to variation in human traits (C.N.S. & B.M.W., unpublished data), perhaps facilitated by social learning (Spottiswoode et al., 2016). ...
Human–wildlife cooperation occurs when humans and free-living wild animals
actively coordinate their behavior to achieve a mutually beneficial outcome.
These interactions provide important benefits to both the human and wildlife
communities involved, have wider impacts on the local ecosystem, and represent
a unique intersection of human and animal cultures. The remaining active forms
are human–honeyguide and human–dolphin cooperation, but these are at risk of
joining several inactive forms (including human–wolf and human–orca cooperation).
Human–wildlife cooperation faces a unique set of conservation challenges,
as it requires multiple components—a motivated human and wildlife partner,
a suitable environment, and compatible interspecies knowledge—which face
threats fromecological and cultural changes. To safeguard human–wildlife cooperation,
we recommend: (i) establishing ethically sound conservation strategies
together with the participating human communities; (ii) conserving opportunities
for human and wildlife participation; (iii) protecting suitable environments;
(iv) facilitating cultural transmission of traditional knowledge; (v) accessibly
archiving Indigenous and scientific knowledge; and (vi) conducting long-term
empirical studies to better understand these interactions and identify threats.
Tailored safeguarding plans are therefore necessary to protect these diverse and
irreplaceable interactions. Broadly, our review highlights that efforts to conserve
biological and cultural diversity should carefully consider interactions between
human and animal cultures.
... These factors can affect how fishers perceive the best conditions for fishing and how they perform the required fishing behaviours to succeed in this traditional fishery. There have been many advances in our understanding of the ecology of dolphins (Romeu et al., 2017, Cantor et al., 2018Machado et al., 2019b;Bezamat et al., 2019) and how fishers interact with them (e.g. Peterson et al., 2008;Catão and Barbosa, 2018;Machado et al., 2019a, da Rosa et al., 2020, but very little attention has been given to how fishers' behavioural variation can influence the dynamics of this fishery. ...
Understanding the dynamics of small-scale fisheries requires considering the diversity of behaviours and skills of fishers. Fishers may have different abilities and tactics that can translate into different fishing outcomes. Here, we investigate variation in fishing behaviours among traditional net-casting fishers that are assisted by wild dolphins, and how this variation interacts with environmental conditions and influences fishing success. By combining in situ environmental sampling with fine-scale behavioural tracking from overhead videos, we found a higher probability of catching fish among fishers well-positioned in the water and that cast their nets wide-open and closer to dolphins. These differences in net-casting performance affect their chance of catching any fish over and above environmental conditions related to fish availability. This finding suggests that fishers’ success may not be simply an outcome of variations in resource availability, but also result from subtle variations in fishing behaviours. We discuss how such behavioural variations can represent skills acquired over the years, and how such skills can be crucial for fishers to benefit and keep interacting with dolphins. Our study demonstrates the role of behavioural variation in the dynamics of a century-old fishery and highlights the need to consider fishers’ behaviours in co-management of small-scale fisheries.
... Finally, T. truncatus whistles usually occur at frequencies up to 30 kHz [59,63]. Specifically, in the T. t. gephyreus population sampled, less than 1% of whistles had part of the fundamental frequency above 24 kHz [64]. Therefore, we can conclude that all sounds produced by T. truncatus can be recorded using a frequency of 48 kHz. ...
Acoustic monitoring in cetacean studies is an effective but expensive approach. This is partly because of the high sampling rate required by acoustic devices when recording high-frequency echolocation clicks. However, the proportion of echolocation clicks recorded at different frequencies is unknown for many species, including bottlenose dolphins. Here, we investigated the echolocation clicks of two subspecies of bottlenose dolphins in the western South Atlantic Ocean. The possibility of recording echolocation clicks at 24 and 48 kHz was assessed by two approaches. First, we considered the clicks in the frequency range up to 96 kHz. We found a loss of 0.95–13.90% of echolocation clicks in the frequency range below 24 kHz, and 0.01–0.42% below 48 kHz, to each subspecies. Then, we evaluated these recordings downsampled at 48 and 96 kHz and confirmed that echolocation clicks are recorded at these lower frequencies, with some loss. Therefore, despite reaching high frequencies, the clicks can also be recorded at lower frequencies because echolocation clicks from bottlenose dolphins are broadband. We concluded that ecological studies based on the presence–absence data are still effective for bottlenose dolphins when acoustic devices with a limited sampling rate are used.
... Fishers benefit from this interaction by catching more fish when the dolphins are present and, supposedly, dolphins accrue similar benefits [17]. For the dolphin population, the interaction has further implications, influencing spatial distribution [19], social behavior [20], acoustic behavior [21], and population dynamics [16]. ...
Background:
Human-animal interactions with mutual benefits in the wild are rare. Such positive interactions seem to require an intricate knowledge from the human side on the animals' behavior and their habitat. In southern Brazil, dolphins and human net-casting fishers have specialized in a cooperative foraging, in which fishers report being able to identify and name dolphins. Here, we evaluate the consensus in their ability to recognize the individual dolphins they interact with. By investigating the reliability of this recognition process, we assess the pros and cons of relying on the fishers' traditional knowledge to further understand the behavior and ecology of dolphins at the individual level. We also assess the potential role of traditional knowledge for the maintenance of this unusual interaction.
Methods:
We interviewed 38 fishers using a semi-structured questionnaire. During each interview, we evaluate their recognition ability of dolphins by showing high-quality photos of dorsal fins of different dolphins, asking questions about the dolphins' behavior and traits, and about how fishers recognize each dolphin. We also evaluated information about the fishers. Different indices were used to measure the fishers' ability to recognize dolphins via photos, and their consensus on individual identification. These indices were modeled as functions of traits of both dolphins and fishers to investigate which ones influence the recognition process.
Results:
We found that fishers can primarily recognize dolphins by natural marks in the dorsal fin but there was little consensus in recognition. Fishers also tend to repeat the name of the most "popular" dolphins for different photos, indicating low reliability in individual recognition. We also found that fishers who learned from relatives (vertical learning) how to interact with dolphins tend to be more accurate and have higher consensus in dolphin recognition than those fishers who learned from friends (horizontal learning) or individually.
Conclusion:
Artisanal fishers have a deep understanding of the dolphins and the system they are inserted in. However, the lack of consensus in identifying individual dolphins herein reported indicates that using their traditional knowledge to further understand dolphin behavior and ecology at the individual level requires caution. Our study also suggests that the transmission of this tradition from parents to sons can be crucial to preserve such a unique human-animal positive interaction in its original form.
... Because the soundscape of a given environment may change over time, variations in dolphin whistles may be the response to varying background noise levels, for example, to facilitate signal transmission and have an effective communication (Ansmann et al., 2007;May-Collado & Wartzok, 2008;Papale, Gamba, Perez-Gil, Martin, & Giacoma, 2015). The changes in vocal behavior may also depend on factors, including group behavior and the occurrence of anthropogenic stressors (Gridley et al., 2017;Hawkins & Gartside, 2009;La Manna, Manghi, Pavan, Lo Mascolo, & Sarà, 2013;Marley, Salgado, & C.P., Erbe, C. and Parnum, I.M., 2017;Rako-Gospić & Picciulin, 2016;Romeu, Cantor, Bezamat, Simões-Lopes, & Daura-Jorge, 2017). The features, such as group size and composition, are also known to influence the acoustic properties of whistles and contribute to their variation (Heiler et al., 2016;Quick & Janik, 2008). ...
The studies on the variation of acoustic communication in different species have provided insight that genetics, geographic isolation, and adaptation to ecological and social conditions play important roles in the variability of acoustic signals. The dolphin whistles are communication signals that can vary significantly among and within populations. Although it is known that they are influenced by different environmental and social variables, the factors influencing the variation between populations have received scant attention. In the present study, we investigated the factors associated with the acoustic variability in the whistles of common bottlenose dolphin (Tursiops truncatus), inhabiting two Mediterranean areas (Sardinia and Croatia). We explored which factors, among (a) geographical isolation of populations, (b) different environments in terms of noise and boat presence, and (c) social factors (including group size, behavior, and presence of calves), were associated with whistle characteristics. We first applied a principal component analysis to reduce the number of collinear whistle frequency and temporal characteristics and then generalized linear mixed models on the first two principal components. The study revealed that both geographic distance/isolation and local environment are associated with whistle variations between localities. The prominent differences in the acoustic environments between the two areas, which contributed to the acoustic variability in the first principal component (PC1), were found. The calf's presence and foraging and social behavior were also found to be associated with dolphin whistle variation. The second principal component (PC2) was associated only with locality and group size, showing that longer and more complex tonal sound may facilitate individual recognition and cohesion in social groups. Thus, both social and behavioral context influenced significantly the structure of whistles, and they should be considered when investigating acoustic variability among distant dolphin populations to avoid confounding factors. K E Y W O R D S acoustic behavior, geographic variation, Mediterranean Sea, Tursiops truncatus
... Dolphins herd schools of fish, mainly mullet, towards fishermen, who stand in shallow water waiting to cast their nets in response to the dolphins' stereotyped behavioural cues (Simões-Lopes et al. 1998, Peterson et al. 2008). This specialized foraging tactic influences the social structure (Daura-Jorge et al. 2012), space use (Cantor et al. 2018) and acoustic repertoire (Romeu et al. 2017) of the dolphins. The interaction has also been shown to influence survival with slightly higher survival rates among dolphins that regularly interact with fishermen . ...
A subset of the bottlenose dolphin Tursiops truncatus gephyreus population in Laguna, southern Brazil, specialize in foraging cooperatively with fishermen. In this study, we describe reproductive parameters for these dolphins and investigate whether this specialized tactic generates reproductive advantages for females that frequently engage in this unusual behavior. We analyzed photo-identification data collected during 233 boat-based surveys during 2007–2009 and 2013–2017. From 27,808 high-quality photographs, we identified and tracked the fate of 24 reproductive females and 45 of their calves. Calving was found to be seasonal, with most births occurring in late spring/summer. The average crude birth rate was 0.09, and estimated fecundity was 0.17. The mean inter-birth interval was 2.09 (for all calves) or 2.43 years (for surviving calves only). Survival to 1 and 2 years estimated by the Kaplan–Meier method was 0.78 (95% CI 0.65–0.92) and 0.65 (95% CI 0.51–0.83), respectively—which represents a survival rate in the second year of 0.83. We investigated the potential influence of birth timing, resource availability, and maternal foraging tactic, home range size and frequency of interaction with fishermen on calf survival. Timing of birth was a significant predictor of calf survival. Giving birth close to the local mullet season would provide lactating females with increased seasonal prey resources, leading to increased calf survival. Due to our sample size (n = 9 cooperative and 15 non-cooperative females), we could not conclude whether or not the cooperative foraging tactic influences calf survival and female reproductive success. We emphasize the importance of long-term monitoring of populations to understand regional life history characteristics and provide accurate information for viability analyses.
... Various studies have examined changes in the acoustic parameters and production rates of whistles in bottlenose dolphins in relation to the behavioural context (Hernandez et al. 2010;Díaz Lopez 2011;May Collado and Quinones-Lebron 2014;Rako Gospić and Picciulin 2016), stress due to separation from conspecifics (Esch et al. 2009), social structure and group composition (Heiler et al. 2016;Romeu et al. 2017) and boat presence and noise levels (Buckstaff 2004;La Manna et al. 2013;Luís et al. 2014;May Collado and Quinones-Lebron 2014;Heiler et al. 2016;Rako Gospić and Picciulin 2016;van Ginkel et al. 2017). These have recently been included as covariates in understanding whistling adaptation in dolphins (May Collado and Quinones-Lebron 2014;Heiler et al. 2016). ...
Bottlenose dolphin communication has been studied extensively. Nevertheless, the combined effect of several variables on whistle structure has yet to be clearly understood. Here, we investigated the influence of underwater noise, boat presence, behaviour, group size and calf presence on the whistles of a small population of common bottlenose dolphins (Tursiops truncatus). Surface behaviour and acoustic data were collected in Sardinia (Italy-Western Mediterranean Sea) between 2015 and 2017. Whistle frequency parameters (minimum, maximum, start, end frequencies and frequency range), duration, number of inflection points and number of harmonics were correlated with the ambient noise levels recorded prior to the whistle display and to behavioural and social factors by means of GAM models. Whistle frequencies varied as a function of the interaction between noise and boat presence, mainly when the noise increased at lower frequencies. Dolphin whistles also varied according to group size, which was further affected by the presence of calves, and behaviours characterised by high levels of arousal such as feeding. The study provides sufficient evidence to support that multiple factors need to be considered when investigating whistle structure as the species is capable of adopting different strategies depending on environmental, social and behavioural context. Finally, this data indicates that communication within a small population of bottlenose dolphins is vulnerable to acoustic pollution, thereby highlighting the need for further investigation into the effects of different noises on whistle structure, as well as the consistency of patterns across different populations.
Significance statement
Exploring a dolphin’s ability to adapt its communication to environmental context is crucial to understanding the consequences of ocean noise increase, especially in highly anthroposised areas such as the Mediterranean Sea. This is one of the few studies that investigate how noise and boat traffic affect bottlenose dolphin whistles whilst considering the concomitant effect of other variables such as behaviour, group size and composition. We demonstrated that dolphins vary their whistles as a function of increasing noise and boat presence, group size and calf presence, and during specific behaviour which requires intense contact between individuals. Finally, the results showed that other variables should be considered to fully understand those which influence whistle structure and adaptability.
... The ecological and socio-economic benefits derived from this dolphin-human tactic have generated emotional affinities in the local community, and motivated a municipal law (No. 521, 10 November 1997) Much of the current literature on Laguna's dolphin population has focused on estimating population parameters (Bezamat et al., 2018;Daura-Jorge et al., 2013), illuminating various different aspects of this dolphin-human interaction (Daura-Jorge et al., 2012;Romeu, Cantor, Bezamat, Simões-Lopes, & Daura-Jorge, 2017;Simões-Lopes et al., 2016) and analysing spatial requirements for individuals with different foraging tactics (Cantor, Simões-Lopes, & Daura-Jorge, 2018). Although the results of our long-term monitoring programme suggest that the apparent survival rate of adults has remained constant from 2007-2016, gillnet bycatch is a local threat (Bezamat et al., 2018). ...
A small population of coastal bottlenose dolphins ( Tursiops truncatus gephyreus ) inhabits the inland waters of Laguna, southern Brazil. A subset of this population interacts with artisanal fishermen. This specialized foraging tactic structures dolphin society into ‘cooperatives' (participants of the interaction) and ‘non‐cooperatives' (non‐participants).
Between 2012 and 2015, a bridge was constructed in Laguna over an important core area for dolphins. Photo‐identification and georeferenced data collected on boat surveys, conducted both before and during bridge construction, were used to evaluate changes in both ‘cooperative' and ‘non‐cooperative' dolphin distribution.
Changes in dolphin distribution were analysed with kernel densities and hurdle models. A grid of 120 cells of area 1 km ² was used to model dolphin distribution, and the minimum distance from the grid cell centre to the bridge and to the area of gillnet use were defined as explanatory variables of human activities. Habitat descriptors (depth and distance) from the lagoon margin were also considered in the model procedure.
Dolphin distribution patterns shifted between periods. A core area used by ‘non‐cooperative' dolphins near the bridge construction works disappeared. The effects of habitat descriptor and anthropogenic activity on dolphin distribution also differed between periods. Before bridge construction, the abundance of ‘non‐cooperative' dolphin was higher close to the bridge area ( p < 0.05). During bridge construction, the presence of ‘cooperative' and ‘non‐cooperative' dolphins decreased significantly with the distance from gillnet fishing activity ( p < 0.01 and p < 0.001 respectively).
This study highlights the importance of accounting for individual variations in response when assessing the effects of a habitat disturbance, or when implementing conservation plans.
... The key finding is that dolphins actively seek to be with similar others outside of the specialized foraging context. Such social affiliations among dolphins that forage in the same way may be reinforced by the differences in vocal repertoires of their social modules [29], which could function in mediating the recognition of preferred affiliates. The homophily around the specialized foraging with net-casting fishermen in Laguna closely resembles the Shark Bay population where the dolphins' associations are structured by homophily around the tactic of using marine sponges as foraging tools [7]. ...
Individuals often associate socially with those who behave the sameway. This principle, homophily, could structure populations into distinct social groups. We tested this hypothesis in a bottlenose dolphin population that appeared to be clustered around a specialized foraging tactic involving cooperation with net-casting fishermen, but in which other potential drivers of such social structure have never been assessed. We measured and controlled for the contribution of sex, age, genetic relatedness, home range and foraging tactics on social associations to test for homophily effects. Dolphins tended to group with others having similar home ranges and frequency of using the specialized foraging tactic, but not other traits. Such social preferences were particularly clear when dolphins were not foraging, showing that homophily extends beyond simply participating in a specific tactic. Combined, these find- ings highlight the need to account for multiple drivers of group formation across behavioural contexts to determine true social affiliations. We suggest that homophily around behavioural specialization can be a major driver of social patterns, with implications for other social processes. If homophily based on specialized tactics underlies animal social structures more widely, then it may be important in modulating opportunities for social learning, and therefore influence patterns of cultural transmission.
... Dolphins that share this foraging tactic associate more often with each other than with the rest of the population, dividing the society into social units of cooperative and noncooperative dolphins (Daura-Jorge et al. 2012). This foraging tactic influences spatial habitat use (dolphins that cooperate more often have smaller home ranges; Cantor et al. 2018); and acoustic repertoires (whistle acoustic parameters vary during the cooperation; Romeu et al. 2017), but its influences on the population dynamics have not previously been entirely explored. ...
Recent years have seen an increasing interest in individual behavioral variation. However, the implications of such variation for population dynamics are often unknown. We studied the dynamics of a bottlenose dolphin (Tursiops truncatus gephyreus) population from southern Brazil, where some individuals forage cooperatively with artisanal fishermen. We fitted mark‐recapture models to 10 yr of photo‐identification data to investigate the influence of this foraging specialization on dolphins’ population parameters, controlling for sex and ranging behavior. We estimated adult survival to be high (0.949 ± 0.015 SE), weakly influenced by home range size, sex or the frequency of interaction with fishermen. The slightly higher survival probability for individuals with smaller home ranges could stem from the benefits of reduced spatial requirements implied by the specialized foraging. Foraging also influenced the probability of resighting individuals, and there was no temporary or permanent emigration. Abundance fluctuated slightly over the years from 54 (95% CI = 49–59) to 60 (95% CI = 52–69) individuals, with no evident population trend. Despite such apparent population stability, we confirm this population remains small and geographically isolated which may threaten its viability and the viability of its unusual, localized foraging specialization. Our study also illustrates how accounting for individual variation can portray animal population dynamics more realistically.
Fishing exclusion zones aim to reduce cetacean bycatch, but often neglect social and ecological side effects, exacerbating social injustices and reshaping fishing practices. We present a case study of an endangered population of Lahille's bottlenose dolphins (Tursiops truncatus gephyreus) in a Brazilian coastal lagoon, known for its unique cooperation with net-casting fishers. However, the local small-scale fisheries (SSF) also employ other fishing gears that contribute to dolphin bycatch, prompting the enforcement of a fishing ban in the area. We investigated fishers' socioeconomic conditions, evidence of social disparities, perceptions on dolphin bycatch, and projected changes on fisheries activities to understand the repercussions of the ban. We categorized 128 surveyed fishers into five groups based on socioeconomic factors and their reliance on dolphin-cooperative and gillnet fisheries. Our findings revealed significant disparities in social capital among fishers and their different attitudes towards dolphin bycatch, highlighting unforeseen consequences. To investigate how fishers would likely shift fishing practices, we considered two management scenarios: 1) should dolphin-fishing cease due to unsuccessful bycatch mitigation, fishing efforts would shift towards shrimp trawling, seine nets, and gillnet effort; 2) if gillnet-fishing is successfully banned as a bycatch mitigation measure, a shift to shrimp trawling and cast net effort. Both scenarios would intensify pressure on shrimp stocks, which are already heavily exploited in this socioecological system. Our research underscores the importance of contemplating alternatives to achieve sustainable outcomes when designing bycatch mitigation measure. Furthermore, our results point to the importance of a participatory governance approach, grounded in the socioeconomic context, to safeguard the livelihoods of small-scale fishers and foster broader conservation efforts beyond species-specific concerns.
• The small population paradigm assumes that populations with low numbers of individuals intrinsically have a high probability of extinction. The small population of Lahille’s bottlenose dolphins Tursiops truncatus gephyreus that specializes in foraging with artisanal fishers in Laguna, southern Brazil, faces human pressures including bycatch in fishing gear. The viability of this population was modelled over 30 and 100 years under different levels of bycatch, including the current scenario of two bycatches every year, two scenarios with higher incidence of bycatches and three management scenarios. The sensitivity of predicted growth rates to fixed-proportion and observed-variation changes in life history parameters was explored.
• The current scenario predicted a declining population (r = −0.014; λ = 0.986) with a high probability of extinction in the long term (PE = 0.71). A small increase in bycatches would result in a marked increase in the probability of extinction. Management scenarios seem promising, but only the zero-bycatch management scenario would make the difference between a declining and an increasing population.
• As expected for slow-growing species, population growth rate was most sensitive to proportional changes in adult female and juvenile survival. However, considering observed variation in vital rates, population dynamics were most influenced by variation in reproductive rates.
• To determine the highest priority for management action, another simulation was made of how additional threat scenarios of recognized human activities (i.e. bycatch influencing adult survival and increased underwater noise or pollution influencing calf survival) would affect population dynamics. Population growth rate was very sensitive to changes in adult bycatch (especially females), as expected, and only subtly sensitive to a reduction in calf survival.
• The current level of bycatch is unsustainable. Bycatch needs to be eliminated to maximize the probability of long-term persistence of this dolphin population. However, this population’s persistence could be threatened by natural variation in reproductive rates.
In northeastern Brazil, two species of delphinids, Steno bredanensis and Tursiops truncatus, are frequently sighted. However, only few studies tried to understand the occurrence of these animals in the places where their records are common. The present study aimed to evaluate the occurrence, habitat use and individual movements of these dolphins in the region of Praia do Forte and in the Abrolhos Bank. The data was derived from the sampling effort of the Instituto Baleia Jubarte (Humpback Whale Institute), opportunistically collected on research and whale-watching vessels during the breeding season of humpback whales, Megaptera novaeangliae, in both study areas. The software ArcGIS 10.3 and R were used to create 50% and 90% Kernel maps for the distribution pattern analysis and to create boxplot graphs for the habitat use analysis, considering the variables depth, distance from the coast, distance from the coral reef and distance from the river mouth. Besides the comparisons between species, the habitat use was also analyzed according to the presence or absence of humpback whales at the time of the encounter with the dolphins. Interspecific interactions were quantified and compared. Photoidentification catalogs were built through the DISCOVERY 2.0.0.43 software and resighting maps were created through ArcGIS 10.3. Results indicated a wide overlap in the distribution of S. bredanensis and T. truncatus in both study areas, yet habitat partitioning occurred only around Praia do Forte. For the records in presence/absence of humpbacks, significant differences in habitat use analysis were also noticed only in the Praia do Forte region. Furthermore, for most of the variables, shorter variations were graphically observed when S. bredanensis was in the presence of whales than otherwise. Interspecific interactions are less expressive in the Abrolhos Bank and, generally, are more common for S. bredanensis than for T. truncatus. Four photo-id catalogs were built and resightings were registered for individuals of both species in both study areas. Due to the distribution patters observed, for both localities, S. bredanensis and T. truncatus were considered as co-occurring species. The habitat use partitioning detected for the Praia do Forte region might be related with the distinct environmental characteristics of both areas. For S. bredanensis, the observed pattern of habitat use with and without humpbacks seems to be related with the foraging tactic performed by these dolphins when using the whales as foraging sites. The recorded resightings indicate potential site fidelity of both species in both study areas, with the exception of T. truncatus in Praia do Forte region. This study enhances the knowledge of these delphinids in Brazilian waters. The systematization of data collection and sampling efforts throughout the year are suggested to increase comprehension on population and spatial patterns, essential for future conservation efforts.
The behavioural context provides opportunities for studying the use and characteristics of acoustic signals. We analysed the context-specific use of acoustic signals in a population of Atlantic spotted dolphins around the Canary archipelago. We calculated the whistle diversity, the mean value of whistle stereotypy and the repetition rate of both tonal and burst-pulsed sounds. Eleven parameters of frequency, signal duration and modulation were measured from each whistle. Results showed that whistle diversity and whistle and chirp repetition rates were negatively correlated with group size, but only whistle diversity and the mean number of stereotypy were related to behavioural activity. Whistles were more complexly modulated during high behavioural activity than when engaged in moderate movements. Furthermore, during socialising and feeding, the highest mean value of stereotypy was displayed, and the parameters of non-stereotyped whistles had lower variability. Our results suggest the use of a complex communication system to improve the efficiency of communication through context-specific signal combinations, the usage of different signals and their modulation pattern. Our study produces evidence to support the hypothesis that acoustic plasticity and differences in call characteristics may be indicative of behavioural and social acoustic environment.
The present study evaluates variations in frequency and duration parameters of whistles of four dolphin species (Sotalia guianensis, Steno bredanensis, Stenella frontalis, and Tursiops truncatus), recorded in the Rio de Janeiro State Coast, Southeastern Brazil. A total of 487 whistles were analyzed. Acoustic parameters of the whistles were classified to species by discriminant function analysis. Overall classification score was 72.5%, with the highest classification score obtained for whistles of S. bredanensis and the lowest obtained for S. frontalis. Most differences were among S. bredanensis and S. guianensis, species that did not have their repertoires compared in other studies.
Animal communication signals are diverse. The types of sounds that animals produce, and the way that information is encoded in those sounds, not only varies between species but can also vary geographically within a species. Therefore, an understanding of the vocal repertoire at the population level is important for providing insight into regional differences in vocal communication signals. One species whose vocal repertoire has received considerable attention is the bottlenose dolphin. This species is well known for its use of individually distinctive identity signals, known as signature whistles. Bottlenose dolphins use their signature whistles to broadcast their identity and to maintain contact with social companions. Signature whistles are not innate, but are learnt signals that develop within the first few months of an animal’s life. It is therefore unsurprising that studies which have characterized signature whistles in wild populations of bottlenose dolphins have provided evidence of geographic variation in signature whistle structure. Here, we describe the occurrence of signature whistles in a previously unexplored wild population of bottlenose dolphins in Cardigan Bay, Wales. We present the first occurrence of a signature whistle with an ultrasonic fundamental frequency component (>30 kHz), a frequency band that was not thought to be utilized by this species for whistle communication. We also describe the occurrence of an ultrasonic non-signature whistle. Our findings highlight the importance of conducting regional studies in order to fully quantify a species’ vocal repertoire, and call into question the efficacy of those studies that use restricted sampling rates.
The 'social complexity hypothesis' suggests that complex social structure is a driver of diversity in animal communication systems. Sperm whales have a hierarchically structured society in which the largest affiliative structures, the vocal clans, are marked on ocean-basin scales by culturally transmitted dialects of acoustic signals known as 'codas'. We examined variation in coda repertoires among both individual whales and social units-the basic element of sperm whale society-using data from nine Caribbean social units across six years. Codas were assigned to individuals using photo-identification and acoustic size measurement, and we calculated similarity between repertoires using both continuous and categorical methods. We identified 21 coda types. Two of those ('1+1+3' and '5R1') made up 65% of the codas recorded, were shared across all units and have dominated repertoires in this population for at least 30 years. Individuals appear to differ in the way they produce '5R1' but not '1+1+3' coda. Units use distinct 4-click coda types which contribute to making unit repertoires distinctive. Our results support the social complexity hypothesis in a marine species as different patterns of variation between coda types suggest divergent functions, perhaps representing selection for identity signals at several levels of social structure.
Selective pressure from the environment on species may select adaptations as a whole, including the specific context of acoustics. Some authors report that the acoustic repertoire of Sotalia guianensis presents dialects as a geographical reflection. However, others propose that the environmental characteristics are the factor that imposes these variations. The present study evaluated if S. guianensis modifies its sound emissions at the Curral Cove (CC) and the Guaraíras Lagoon Complex (GLC), different habitats at similar latitudes. At the GLC, dolphins use higher whistle frequencies as well as higher number of click per second, facts that may be related to sound precision for communication between individuals and prey capture. Variations in the dolphins’ sounds may be related to differences in the environments such as natural background noise—biotic and abiotic—and characteristics such as turbidity, temperature, salinity, and modification in sound propagation due to depth and bottom properties. The pulsed calls’ sound category did not present modification between habitats probably due to context in which they are used since they occur during high physical contact. It is possible that the variation of the sound parameters between the CC and GLC environments is a reflection of the species’ adaptive potential, since a population can adjust the sounds emitted by its individuals to the environment’s features, revealing acoustic plasticity.
A pressão seletiva do ambiente sobre as espécies ali viventes pode selecionar adaptações como um todo, inclusive no contexto acústico específico. Alguns autores relatam que o repertório acústico de Sotalia guianensis apresenta dialetos como reflexo geográfico; entretanto, outros autores propõem que as características do ambiente são o fator que impõem essas variações. O presente estudo avaliou se S. guianensis modifica suas emissões sonoras entre a Enseada do Curral (CC) e o Complexo Lagunar de Guaraíras (GLC), habitats diferentes localizados em latitudes semelhantes. No GLC, os golfinhos utilizam frequências mais altas de assobios assim como maior número de cliques por segundo, fatos que podem estar relacionados com a precisão dos sons para a comunicação entre indivíduos e a captura de presas. As variações nos sons dos golfinhos podem estar relacionadas às diferenças nos ambientes, como ruídos de fundo naturais—bióticos e abióticos—características como turbidez, temperatura e salinidade; e modificação da propagação do som devido profundidade e propriedades do fundo. A categoria sonora grito não apresentou modificação entre os habitas provavelmente devido ao contexto em que são usados, pois ocorrem durante alto contato físico entre os indivíduos. É possível que a variação dos parâmetros sonoros entre os ambientes de CC e GLC seja reflexo do potencial adaptativo da espécie, pois uma mesma população pode ajustar os sons emitidos pelos seus indivíduos às características do ambiente revelando uma plasticidade acústica.
Dolphins fishing alone in open waters may whistle without interrupting their sonar clicks as they find and eat or reject fish. Our study is the first to match sound and video from the dolphin with sound and video from near the fish. During search and capture of fish, free-swimming dolphins carried cameras to record video and sound. A hydrophone in the far field near the fish also recorded sound. From these two perspectives, we studied the time course of dolphin sound production during fish capture. Our observations identify the instant of fish capture. There are three consistent acoustic phases: sonar clicks locate the fish; bout 0.4 sec before capture, the dolphin clicks become more rapid to form a second phase, the terminal buzz; at or just before capture, the buzz turns to an emotional squeal-the victory squeal, which may last 0.2 to 20 sec after capture. The squeals are pulse bursts that vary in duration, peak frequency, and amplitude. The victory squeal may be a reflection of emotion triggered by brain dopamine release. It may also affect prey to ease capture and or it may be a way to communicate the presence of food to other dolphins.
Dolphins also use whistles as communication or social sounds. Whistling during sonar clicking suggests that dolphins may be adept at doing two things at once. We know that dolphin brain hemispheres may sleep independently. Our results suggest that the two dolphin brain hemispheres may also act independently in communication.
Multilevel societies, containing hierarchically nested social levels, are remarkable social structures whose origins are unclear. The social relationships of sperm whales are organized in a multilevel society with an upper level composed of clans of individuals communicating using similar patterns of clicks (codas). Using agent-based models informed by an 18-year empirical study, we show that clans are unlikely products of stochastic processes (genetic or cultural drift) but likely originate from cultural transmission via biased social learning of codas. Distinct clusters of individuals with similar acoustic repertoires, mirroring the empirical clans, emerge when whales learn preferentially the most common codas (conformism) from behaviourally similar individuals (homophily). Cultural transmission seems key in the partitioning of sperm whales into sympatric clans. These findings suggest that processes similar to those that generate complex human cultures could not only be at play in non-human societies but also create multilevel social structures in the wild.
The Guiana dolphin produces a variable whistle
repertoire related to different social contexts. The current
study evaluates Guiana dolphin whistles at a microscale.
Acoustic parameters ofwhistles were compared between three
areas in southeastern Brazil using a recording system with
sampling rate of 96 kHz. Previous studies that utilized a
sampling rate of 48 kHz reported little variation between
adjacent areas in Brazil. Nine acoustic parameters of the
whistles (duration, start, end, minimum and maximum frequencies,
delta frequency, frequency at 1/4, 1/2, and 3/4 of
duration) were measured and whistles were classified into five
contour forms. A total of 659 whistles were analyzed, of
which 62.20 % showed an ascending contour form. The
Guiana dolphin emitted whistles with a fundamental frequency
reaching 44.9 kHz. Dolphin whistles from the three study
areas varied significantly in nine acoustic parameters. The
whistle duration was shorter (272.44±105.25 ms) in
Guanabara Bay than those in Sepetiba (360.05±135.16 ms)
and Paraty Bays (376.80±159.78 ms). The start and minimum
frequencies of the whistles in Guanabara Bay was significantly
higher than those in Sepetiba and Paraty Bays. The results
of discriminant function analysis indicated a significant difference
between Guanabara Bay and the other two areas.
Comparisons of the ascending, descending–ascending, and
multi whistles between areas showed differences in some
acoustic parameters. In this study, by doubling the sampling
rate in our recording systems, we were able to more accurately
sample the whistle repertoire of Guiana dolphins in southeastern
Brazil, and thereby detect differences in whistles between
neighboring populations.
Many animals produce vocal sequences that appear complex. Most researchers assume that these sequences are well characterized as Markov chains (i.e. that the probability of a particular vocal element can be calculated from the history of only a finite number of preceding elements). However, this assumption has never been explicitly tested. Furthermore, it is unclear how language could evolve in a single step from a Markovian origin, as is frequently assumed, as no intermediate forms have been found between animal communication and human language. Here, we assess whether animal taxa produce vocal sequences that are better described by Markov chains, or by non-Markovian dynamics such as the 'renewal process' (RP), characterized by a strong tendency to repeat elements. We examined vocal sequences of seven taxa: Bengalese finches Lonchura striata domestica, Carolina chickadees Poecile carolinensis, free-tailed bats Tadarida brasiliensis, rock hyraxes Procavia capensis, pilot whales Globicephala macrorhynchus, killer whales Orcinus orca and orangutans Pongo spp. The vocal systems of most of these species are more consistent with a non-Markovian RP than with the Markovian models traditionally assumed. Our data suggest that non-Markovian vocal sequences may be more common than Markov sequences, which must be taken into account when evaluating alternative hypotheses for the evolution of signalling complexity, and perhaps human language origins.
To improve our understanding of the complex genetic and ecological structure of bottlenose dolphin ( Tursiops truncatus ) populations, we examined the acoustic features of communication signals from two geographically contiguous areas: the Central–Eastern North Atlantic and the Mediterranean Sea. Variations in the whistles were evaluated for four locations. Ten signal parameters were measured and used to statistically differentiate between the areas. Over 79 % of sightings were correctly classified by discriminant function analysis, confirming an acoustic differentiation between the two basins. The results of cluster analysis using the mean values of the parameters for each sighting showed that the three easternmost sightings from the Mediterranean and one sighting from the Canary archipelago formed a separate cluster from the rest of the Atlantic. The two sightings from the Alboran Sea in the west Mediterranean were grouped with the Atlantic recordings. There was more variability in whistles from the Atlantic Ocean consistent with data from genetic and photo-identification studies that document resident and non-resident animals in the area. The results suggest that the Alboran area may be inhabited by animals differentiated from the rest of the Mediterranean basin as a result of habitat features.
Communication among animals should use signals that are most efficient in their particular habitat. Here, we report data from 3 populations of Indo-Pacific bottlenose dolphins (Tursiops aduncus) in Japan that produce whistles transmitted efficiently through environmental ambient noise. We compared the characteristics of the ambient noise in the dolphins' habitats and the whistles produced. In habitats with less ambient noise, dolphins produced whistles at varying frequencies with greater modulations; when ambient noise was greater, dolphins produced whistles of lower frequencies with fewer frequency modulations. Examination of our results suggests that communication signals are adaptive and are selected to avoid the masking of signals and the attenuation of higher-frequency signals. Thus, ambient noise may drive the variation in whistles of Indo-Pacific bottlenose dolphin populations.
Whistles are narrowband, frequency-modulated sounds produced by many cetaceans. Whistles are extensively studied in delphinids, where several factors have been proposed to explain between- and within-species variation. We examined factors associated with geographic variation in whistles of common bottlenose dolphins (Tursiops truncatus) by assessing the role of ambient noise, noise from boats, and sympatry with other dolphin species, and reviewing and comparing whistle structure across populations in the western and eastern Atlantic Ocean. Whistles of adjacent populations differed, particularly in frequency parameters. A combination of factors may contribute to microgeographic whistle variation, including differences in ambient noise levels (dolphins produced relatively higher frequency whistles in the noisiest habitat), and differences in number of boats present (when multiple boats were present, dolphins whistled with greater frequency modulation and whistles were higher in maximum frequency and longer than when a single boat was present). Whistles produced by adjacent populations were relatively similar in structure. However, for clearly separated populations, the distance between them did not relate directly to whistle structure. We propose that plasticity in bottlenose dolphin whistles facilitates adaptation to local and changing conditions of their habitat, thus promoting variation between populations at different geographic scales.
A detailed analysis of the interactions between Tursiops /runco/us
(Montagu, 1821) and the artisanal fishing of mullets (MugU spp.) is presented at two
localities in the south of Brazil: Laguna (Santa Catarina) and Imberrramandai (Rio
Grande do Sui). Its behavioral strategies and the advantages of their association are
re-described and quantified based on the success of the capture and on the selectivity
of the prey sizes. The mullets are the main resource involved (92 % to 75%) both at
numerical level and as biomass. Twenty individuals ofTursiops /runcollls participated
in the interactions in Laguna and 9 in Imberrramandai. The participation and learning
of calves is also reported.
KEY WORDS. Cetacea, Delphinidae, TUl'siops lrunco/us, ecology, behavior, artisanal
fishery.
Bottlenose dolphins (Tursiops truncatus) produce individually distinctive signature whistles that broadcast the identity of the caller. Unlike voice cues that affect all calls of an animal, signature whistles are distinct whistle types carrying identity information in their frequency modulation pattern. Signature whistle development is influenced by vocal production learning. Animals use a whistle from their environment as a model, but modify it, and thus invent a novel signal. Dolphins also copy signature whistles of others, effectively addressing the whistle owner. This copying occurs at low rates and the resulting copies are recognizable as such by parameter variations in the copy. Captive dolphins can learn to associate novel whistles with objects and use these whistles to report on the presence or absence of the object. If applied to signature whistles, this ability would make the signature whistle a rare example of a learned referential signal in animals. Here, we review the history of signature whistle research, covering definitions, acoustic features, information content, contextual use, developmental aspects, and species comparisons with mammals and birds. We show how these signals stand out amongst recognition calls in animals and how they contribute to our understanding of complexity in animal communication.
Culture is increasingly being understood as a driver of mammalian phenotypes. Defined as group-specific behaviour transmitted by social learning, culture is shaped by social structure. However, culture can itself affect social structure if individuals preferentially interact with others whose behaviour is similar, or cultural symbols are used to mark groups. Using network formalism, this interplay can be depicted by the coevolution of nodes and edges together with the coevolution of network topology and transmission patterns. We review attempts to model the links between the spread, persistence and diversity of culture and the network topology of non-human societies. We illustrate these processes using cetaceans. The spread of socially learned begging behaviour within a population of bottlenose dolphins followed the topology of the social network, as did the evolution of the song of the humpback whale between breeding areas. In three bottlenose dolphin populations, individuals preferentially associated with animals using the same socially learned foraging behaviour. Homogeneous behaviour within the tight, nearly permanent social structures of the large matrilineal whales seems to result from transmission bias, with cultural symbols marking social structures. We recommend the integration of studies of culture and society in species for which social learning is an important determinant of behaviour.
Animal tool use is of inherent interest given its relationship to intelligence, innovation and cultural behaviour. Here we investigate whether Shark Bay bottlenose dolphins that use marine sponges as hunting tools (spongers) are culturally distinct from other dolphins in the population based on the criteria that sponging is both socially learned and distinguishes between groups. We use social network analysis to determine social preferences among 36 spongers and 69 non-spongers sampled over a 22-year period while controlling for location, sex and matrilineal relatedness. Homophily (the tendency to associate with similar others) based on tool-using status was evident in every analysis, although maternal kinship, sex and location also contributed to social preference. Female spongers were more cliquish and preferentially associated with other spongers over non-spongers. Like humans who preferentially associate with others who share their subculture, tool-using dolphins prefer others like themselves, strongly suggesting that sponge tool-use is a cultural behaviour.
Bottlenose dolphins (Tursiops truncatus) are an extremely vocal mammalian species and vocal communication plays an important role in mediating social interactions. Very little is known about how wild bottlenose dolphins use whistles in different contexts and no data exist for context specificity of whistle characteristics. This study describes, for the first time in the Mediterranean Sea, the whistle characteristics of bottlenose dolphins in their natural repertoire. Over 35 h of behavioural observations and simultaneous recordings, 3032 tonal, frequency modulated whistles were detected. Our findings further support, for the first time in wild bottlenose dolphins, the suggestion that acoustic features may be good predictors of behavioural state and vice versa. These results advocate that these parameters may be used to communicate specific information on the behavioural context of the individuals involved. Additionally, visual inspection reveals that upsweeps and multi-looped whistles play an important role in the natural communication system of bottlenose dolphins. Likewise, this study demonstrates how dynamic bottlenose dolphin whistle characteristics are and how important it is to consider many factors in analysis. High intra-specific variability in whistle characteristics demonstrates its integral role in the complex social lives of wild bottlenose dolphins.
Analyses of intraspecific variation in behaviour can provide insights into the process of be-havioural diversification. In this study we characterized geographic variation in whistle struc-ture of the estuarine dolphin, Sotalia guianensis, at 10 sites of a ∼4000 km transect along the coast of Brazil. Whistles were recorded, digitized (N = 527), and six acoustic parameters measured from spectrograms. ANOVA revealed geographic variation in all six parameters. Post-hoc analyses indicated that pairs of sites with similar whistle parameters tended to be adjacent to each other, and discriminant functions analysis (DFA) revealed that the greatest differences in whistle structure tended to occur between the most distant sites. Whistle para-meters did not, however, express simple clinal variation, and DFA was a poor predictor of site (29.0% accuracy). Mantel tests revealed significant correlations between geographic distance and variation in three of six whistle parameters. Linear regression analyses for our data set, pooled with data from Azevedo & Van Sluys (2005, J. Acoust. Soc. Am. 117:1456), revealed significantly lower starting and minimum frequencies for southern populations relative to northern populations. A geographic discontinuity in these two features is observed, varying on either side of the easternmost tip of South America. Possible ecological and evolutionary explanations for these patterns are discussed.
A bstract
This paper examines environmental and behavioral determinants of the habitat use and preferences of Indo‐Pacific humpback dolphins inhabiting the Algoa Bay region on the south Eastern Cape coast of South Africa. In order to quantify the habitat use and preference, two indices were used, the Coefficient of Area Use (AU) and the Activity Index (AI). The dolphins inhabit a narrow strip of shallow, inshore waters of Algoa Bay and remain mostly within 400 m of the shore, in water less than 15 m deep, with no apparent preference for clear or turbid water. Water depth is probably the main factor limiting their inshore distribution, and the 25‐m isobath seems to represent the critical depth. Within this confined, inshore distribution, dolphin activities concentrate in the vicinity of rocky reefs‐their primary feeding grounds. Dolphin dependence on these shallow‐water habitats is evident throughout the year and, consequently, the inshore shallow reefs are identified as the “key habitat” which is of primary importance for humpback dolphins in Eastern Cape waters. The dolphins' dependence on this restricted type of habitat within an already restricted inshore distribution makes them particularly vulnerable to alteration or loss of this habitat.
Diverse and localized foraging behaviours have been reported in isolated populations of many animal species around the world. In Laguna, southern Brazil, a subset of resident bottlenose dolphins (Tursiops truncatus) uses a foraging tactic involving cooperative interactions with local, beach-casting fishermen. We used individual photo-identification data to assess whether cooperative and non-cooperative dolphins were socially segregated. The social structure of the population was found to be a fission-fusion system with few non-random associations, typical for this species. However, association values were greater among cooperative dolphins than among non-cooperative dolphins or between dolphins from different foraging classes. Furthermore, the dolphin social network was divided into three modules, clustering individuals that shared or lacked the cooperative foraging tactic. Space-use patterns were not sufficient to explain this partitioning, indicating a behavioural factor. The segregation of dolphins using different foraging tactics could result from foraging behaviour driving social structure, while the closer association between dolphins engaged in the cooperation could facilitate the transmission and learning of this behavioural trait from conspecifics. This unique case of a dolphin-human interaction represents a valuable opportunity to explore hypotheses on the role of social learning in wild cetaceans.
Communication among animals should use signals that are most efficient in their particular habitat. Here, we report data from 3 populations of Indo-Pacific bottlenose dolphins (Tursiops aduncus) in Japan that produce whistles transmitted efficiently through environmental ambient noise. We compared the characteristics of the ambient noise in the dolphins' habitats and the whistles produced. In habitats with less ambient noise, dolphins produced whistles at varying frequencies with greater modulations; when ambient noise was greater, dolphins produced whistles of lower frequencies with fewer frequency modulations. Examination of our results suggests that communication signals are adaptive and are selected to avoid the masking of signals and the attenuation of higher-frequency signals. Thus, ambient noise may drive the variation in whistles of Indo-Pacific bottlenose dolphin populations.
The sonar of dolphins has undergone evolutionary re-finement for millions of years and has evolved to be the premier sonar system for short range applications. It far surpasses the capability of technological sonar, i.e. the only sonar system the US Navy has to detect buried mines is a dolphin system. Echolocation experiments with captive animals have revealed much of the basic parameters of the dolphin sonar. Features such as signal characteristics, transmission and reception beam patterns, hearing and internal filtering properties will be discussed. Sonar detection range and discrimination capabilities will also be included. Recent measurements of echolocation signals used by wild dolphins have expanded our understanding of their sonar system and their utilization in the field. A capability to perform time-varying gain has been recently uncovered which is very different than that of a technological sonar. A model of killer whale foraging on Chinook salmon will be examined in order to gain an understanding of the effectiveness of the sonar system in nature. The model will examine foraging in both quiet and noisy environments and will show that the echo levels are more than sufficient for prey detection at relatively long ranges.
Understanding and documenting the characteristics and features of the social sounds and associated behavior of free-ranging delphinids has historically been limited by lack of access to animals and poor underwater viewing conditions. Communication studies of delphinids have been undertaken in both captivity (see Herman and Tavolga 1980 for review) and in the wild (Connor et al. 1992; Norris et al. 1994). Even with a wealth of information about dolphin sound production and hearing capabilities from captivity, there are significant gaps in understanding how dolphins detect, decode, and decipher both their environmental and social signals in the wild. Although the abilities of dolphins to actively produce both echolocation signals and social sounds have been documented, little is understood about the sensory exposure and information available to, and utilized by, free-ranging delphinids. One way to address this issue is to review the use of conspecific social signals and behavior. Dolphins, like other animals, have been under evolutionary pressures for increased efficiency in their communication system. By observing critical environmental and social aspects of delphinid society we might gain insight into how these animals learn and selectively filter information in their environment.
Food-related signalling is widespread in the animal kingdom with some food-associated vocalizations considered functionally referential. Food calls can, however, vary greatly in the type of information they convey. Thus, there are a multitude of purposes for which food calls are used, including social recruitment, caller spacing, the indication of type, quantity, quality, divisibility of food, the caller’s hunger level and even as tools to manipulate prey behaviour. Yet little work has focused on the social aspect of food calling in animals. We investigated the association of social signals in wild bottlenose dolphins with foraging behaviour where context-specific food-associated calls are commonly produced. Our data showed that specific social signals were significantly correlated with food call production and these calls rarely occurred in the absence of food calls. We suggest that animals are sharing additional information on the food patch itself with their social affiliates.
Recent studies have proposed latitudinal variations for the whistles of Sotalia guianensis, since parameters of frequency increase from the southernmost distribution of the species (State of Santa Catarina, Brazil) toward the North. The last study on the whistles of S. guianensis, conducted in Costa Rica, confirmed the geographical variation of whistles, regardless of frequency responses used in the samples. Initial and minimum frequencies of whistles of the Costa Rican populations were higher than were the frequencies of Brazilian populations. In this current study, the whistles of S. guianensis were recorded with a sampling frequency of 48 kHz, the highest frequency band used in Brazilian studies. The initial and minimum frequency of whistles recorded and analyzed were similar to parameters of Costa Rican populations and show little or no difference when compared to the average of each study. Therefore, whistle frequency variables do not increase with latitude. It is likely that variations in acoustic parameters S. guianensis are mainly linked to environmental characteristics of the habitats in which the populations occur. Thus, the repertoire sound S. guianensis appears linked to similar environments with similar physical characteristics and not linked to population characteristics (dialects).
Although killer whale, Orcinus orca, dialects have been studied in detail in several populations, little attempt has been made to compare dialect characteristics between populations. In this study we investigated geographical variation in monophonic and biphonic calls among four resident populations from the North Pacific Ocean: Northern and Southern residents from British Columbia and Washington State, southern Alaska residents, and eastern Kamchatka residents. We tested predictions generated by the hypothesis that call variation across populations is the result of an accumulation of random errors and innovation by vertical cultural transmission. Call frequency contours were extracted and compared using a dynamic time-warping algorithm. We found that the diversity of monophonic calls was substantially higher than that of biphonic calls for all populations. Repertoire diversity appeared to be related to population size: in larger populations, monophonic calls were more diverse and biphonic calls less diverse. We suggest that the evolution of both monophonic and biphonic calls is caused by an interaction between stochastic processes and directional selection, but the relative effect of directional selection is greater for biphonic calls. Our analysis revealed no direct correlation between call repertoire similarity and geographical distance. Call diversity within predefined call categories, types and subtypes, showed a high degree of correspondence between populations. Our results indicate that dialect evolution is a complex process influenced by an interaction among directional selection, horizontal transmission and founder effects. We suggest several scenarios for how this might have arisen and the implications of these scenarios for call evolution and population history.
We examined the hypothesis that dolphins increase their rate of sound production during feeding events to recruit new individuals. We recorded 135.5 min of underwater sounds from bottlenose dolphins (Tursiops truncatus) near Isla del Coco, Costa Rica. Data were collected from eight feeding groups and three nonfeeding groups. We classified sounds as whistles, click trains, or pulse bursts. The number of whistles per min per dolphin was higher in feeding groups than in non- feeding groups. More whistles than click trains or pulse bursts were produced when dolphins were feeding. On the other hand, there was no differ- ence in the proportion of each sound type produced when dolphins were not feeding. New dolphins joined the feeding events for which we recorded dolphin sounds. Results supported the hypothesis that dolphin group size increases in response to an increase in the number of whistles by conspecif- ics; however, confounding factors, such as the use of specific feeding calls, need to be accounted for to support the increased sound-rate hypothesis.
In animal communication research, vocal labeling refers to incidents in which an animal consistently uses a specific acoustic signal when presented with a specific object or class of objects. Labeling with learned signals is a foundation of human language but is notably rare in nonhuman communication systems. In natural animal systems, labeling often occurs with signals that are not influenced by learning, such as in alarm and food calling. There is a suggestion, however, that some species use learned signals to label conspecific individuals in their own communication system when mimicking individually distinctive calls. Bottlenose dolphins (Tursiops truncatus) are a promising animal for exploration in this area because they are capable of vocal production learning and can learn to use arbitrary signals to report the presence or absence of objects. Bottlenose dolphins develop their own unique identity signal, the signature whistle. This whistle encodes individual identity independently of voice features. The copying of signature whistles may therefore allow animals to label or address one another. Here, we show that wild bottlenose dolphins respond to hearing a copy of their own signature whistle by calling back. Animals did not respond to whistles that were not their own signature. This study provides compelling evidence that a dolphin's learned identity signal is used as a label when addressing conspecifics. Bottlenose dolphins therefore appear to be unique as nonhuman mammals to use learned signals as individually specific labels for different social companions in their own natural communication system.
A subgroup of a population of Tursiops truncatus in southern Brazil is known
for a cooperative behavior with artisanal fishermen whereby the dolphins shoal
fish towards net-casting fishermen. Combining photo-identification data collected
between September 2007 and 2009 with mark-recapture and Pollock’s robust design
models, we assessed abundance within seasons and survival and temporary
emigration rates of dolphins between seasons. We also reanalyzed a previous data
set collected during 1989–1991, and Cormack-Jolly-Seber models were applied to
estimate survival rates for each of the study periods. The abundance of marked “cooperative”
dolphins varied between seasons from 18 (CI: 17–24) to 21 (CI: 20–24).
The total abundance varied from 59 in the winter of 2008 (CI: 49–72) to 50 in the
autumn of 2009 (CI: 40–62). The annual adult survival was estimated to be 0.917
(CI: 0.876–0.961), close to that estimated from data collected in the 1990s (0.941;
CI: 0.888–0.998). The emigration probability was low (0.031; CI: 0.011–0.084)
and different capture probabilities between the “cooperative” and “noncooperative”
dolphins indicated a degree of behavioral segregation. The precision of our estimates
is likely to provide sufficient power to detect population change, but we recommend
a precautionary management approach to protect this vulnerable dolphin
community and its unique cooperative feeding tradition.
Most animal communication has evolved and now takes place in the context of a communication network, i.e. several signallers and receivers within communication range of each other. This idea follows naturally from the observation that many signals travel further than the average spacing between animals. This is self evidently true for long-range signals, but at a high density the same is true for short-range signals (e.g. begging calls of nestling birds). This book provides a current summary of research on communication networks and appraises future prospects. It combines information from studies of several taxonomic groups (insects to people via fiddler crabs, fish, frogs, birds and mammals) and several signalling modalities (visual, acoustic and chemical signals). It also specifically addresses the many areas of interface between communication networks and other disciplines (from the evolution of human charitable behaviour to the psychophysics of signal perception, via social behaviour, physiology and mathematical models).
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.
Properties of the tonal calls of cetaceans are summarised and compared at the species level. Statistics are presented relating to start, end, minimum, maximum and centre frequencies, duration and number of inflections, together with information about recordings (location, number encounters/groups, length of recordings). Evidence of a linear relation between body-size and wavelength is given for odontocetes (R between 0.68 and 0.93, depending on frequency variable and least-squares method) but the relationship does not appear to fit well for mysticetes (R = 0.64). Results of preliminary investigations into acoustic discrimination of species by multivariate methods are also presented: a simple classifier for 10 species based on results derived from the literature gave a correct classification rate of 28% when tested with independent data. Some methodological recommendations for future descriptive work on cetacean acoustics are made.
Whistle vocalizations of five odontocete cetaceans, the false killer whale P.
crassidens, short-finned pilot whale G.
macrorhynchus, long-finned pilot whale G.
melas, white-beaked dolphin L.
albirostris and Risso's dolphin G.
griseus, were analysed and summarized quantitatively. Recordings were acquired from a number of locations and encounters. Significant differences were found between species and, to a lesser extent, between locations. The calls of the two pilot whale species are distinct despite their close relatedness, and similar size and morphology. This may be due to selection pressures to maintain distinctiveness. The variance was partitioned into between-species, between-location (within species) and within-location factors. For the frequency variables, variation between-species is high relative to variation between locations. Thus geographic variation is a relatively minor effect, compared to the many processes which cause interspecific differences. The within-location component includes such factors as social context, behaviour and group composition. This component is of a similar magnitude to the between-species component, indicating that whistles vary considerably with these factors. Significant between-location differences may be attributable to these confounding factors. For whistle duration, most of the variation occurred within location. There is less significant variation in duration across species compared with the frequency measures. This study highlights the need to collect samples across all potential strata whenever possible, and provides a framework for future, more comprehensive work.
A bstract
Acoustic methods may improve the ability to identify cetacean species during shipboard surveys. Whistles were recorded from nine odontocete species in the eastern tropical Pacific to determine how reliably these vocalizations can be classified to species based on simple spectrographic measurements. Twelve variables were measured from each whistle ( n = 908). Parametric multivariate discriminant function analysis (DFA) correctly classified 41.1% of whistles to species. Non‐parametric classification and regression tree (CART) analysis resulted in 51.4% correct classification. Striped dolphin whistles were most difficult to classify. Whistles of bottlenose dolphins, false killer whales, and pilot whales were most distinctive. Correct classification scores may be improved by adding prior probabilities that reflect species distribution to classification models, by measuring alternative whistle variables, using alternative classification techniques, and by localizing vocalizing dolphins when collecting data for classification models.
Dolphins are adept at learning new vocalizations (whistles) throughout life, an ability thus far demonstrated in few nonhuman mammals. In dolphins, this ability is well documented in captivity but poorly studied in the wild, and little is known of its role in natural social behavior. This study documents the previously unknown phenomenon of whistle convergence among habituated free-living male bottlenose dolphins (Tursiops sp.). Over a 4 yr study period, three male subjects formed an alliance, spending most of their time together and cooperating to herd females. Within individuals, whistle repertoires were more variable than expected based on previous studies, mostly performed with captive dolphins, but became less so during the course of the study. Among individuals, the distinctiveness of individual repertoires decreased such that the three males were virtually indistinguishable by the end of the study. Initially, some whistle types were shared. By the end of the study, the three males had formed a close alliance, and had all converged on one particular shared whistle form which they had rarely produced before forming the alliance. The results are discussed in terms of their implications for the prevailing ‘signature whistle’ hypothesis, as well as possible mechanisms and functional significance of whistle convergence among cooperating males.
The signature whistle hypothesis states that dolphins produce highly stereotyped, individually distinctive whistles when in isolation. The presence of signature whistles has been called into question by recent studies proposing that dolphins produce a shared, simple upsweep whistle when in isolation, and that whistles produced by socializing dolphins are shared across individuals and social groups. This shared repertoire hypothesis suggests that when two animals produce the same whistle type, it is due to sharing the same common repertoire rather than one animal learning to produce the whistle of another. One difference between studies supporting or denying the existence of signature whistles is the method used to classify whistle types. We examined whistle production by 17 free-ranging bottlenose dolphins while temporarily restrained. We used both a quantitative comparison technique similar to that used to support the shared repertoire hypothesis and human judges to classify whistle types and quantify similarity between types. Contrary to recent studies that emphasize shared whistles, overall whistle sharing between isolated individuals was low (25%) and a simple upsweep did not account for the most common whistle type in half of the animals. Some species of birds, bats, and primates with stable social groups use vocal learning to converge over time to one common group distinctive call type. We examined whistle similarity between adult male dolphins that are partners in a close social alliance in order to test whether vocal learning may enable a similar vocal convergence. Whistle similarity was rated very high between partners and low between non-partners by both the quantitative technique and human observers. This suggests that as in songbirds and some other mammals, adult male bottlenose dolphins may use vocal learning to converge on similar whistles as they develop affiliative social relationships.
Pure tonal whistle vocalizations from five species of dolphins found in the western North Atlantic had consistent, species-specific characteristics. The degree of differences between species, as based on the results of multivariate discriminant analysis (Fig. 2), correlated with the taxonomic and zoogeographic relations of the five dolphin species. Congeneric species had more similar vocalizations than species of different genera. Differences between sympatric species were greater than differences between allopatric species. Of the six whistle parameters measured, maximum frequency had the lowest coefficient of variation for all five species, and duration and number of inflection points had the highest coefficients of variation for all five species.
Humpback whale songs recorded on tropical calving grounds exhibit different dialects depending on the oceanic basin. Songs sampled simultaneously from two populations in the North Pacific (Hawaii and Mexico) were essentially identical. These North Pacific songs were clearly different from the song type shared by two populations in the North Atlantic (Cape Verde Islands and West Indies). Songs from the Southern Hemisphere (Tonga) represent a third distinct dialect. Our evidence shows that, despite annual change in song organization, significant differences in humpback song occur between isolated ocean basins, while only subtle differences exist within an oceanic population (Hawaii and Pacific Mexico).