Cross-modal perception of identity by sound and taste in bottlenose dolphins

Aerial urination in Amazon river dolphins: reassessing its social significance and implications for sensory biology

Araújo-Wang et al. (2025) reported on aerial urination events in male Amazon river dolphins (Inia araguaiaensis) from the Tocantins River in Brazil, a phenomenon that appears to occur across populations of Inia. The authors argue that this behavior would be indicative of a yet undescribed sensory modality in these animals and that it probably represents an intrasexual display of dominance. However, both of these claims do not appear plausible in light of the limited available data. If indeed functional, aerial urination is more parsimoniously explained as a form of solo or social play.

A multidimensional approach to the self in non-human animals through the Pattern Theory of Self

In the last decades, research on animal consciousness has advanced significantly, fueled by interdisciplinary contributions. However, a critical dimension of animal experience remains underexplored: the self. While traditionally linked to human studies, research focused on the self in animals has often been framed dichotomously, distinguishing low-level, bodily, and affective aspects from high-level, cognitive, and conceptual dimensions. Emerging evidence suggests a broader spectrum of self-related features across species, yet current theoretical approaches often reduce the self to a derivative aspect of consciousness or prioritize narrow high-level dimensions, such as self-recognition or metacognition. To address this gap, we propose an integrated framework grounded in the Pattern Theory of Self (PTS). PTS conceptualizes the self as a dynamic, multidimensional construct arising from a matrix of dimensions, ranging from bodily and affective to intersubjective and normative aspects. We propose adopting this multidimensional perspective for the study of the self in animals, by emphasizing the graded nature of the self within each dimension and the non-hierarchical organization across dimensions. In this sense, PTS may accommodate both inter- and intra-species variability, enabling researchers to investigate the self across diverse organisms without relying on anthropocentric biases. We propose that, by integrating this framework with insights from comparative psychology, neuroscience, and ethology, the application of PTS to animals can show how the self emerges in varying degrees and forms, shaped by ecological niches and adaptive demands.

Balance between stability and variability in bottlenose dolphin signature whistles offers potential for additional information

Bottlenose dolphins produce individually distinctive signature whistles (SWs) to broadcast identity. Stability of the SW frequency contour is essential to preserve identity information; however, SWs could carry additional information which requires variability. We used acoustic recordings from provisioned free-swimming Indo-Pacific bottlenose dolphins at Moreton Island (Mulgumpin), Australia, collected in 2002 and 2017-2018, to assess the long-term (15-year) stability in SWs, and if variability of acoustic parameters increases with whistle complexity. Stability was assessed by analyzing basic contour parameters (minimum and maximum frequency, duration, etc.) and visually. We quantified SW variability using two developed variability metrics. Complexity was defined using four developed metrics, and its effect on variability was tested. Our results demonstrated that SW contours remain highly stable over time, but minimum frequency decreased by 8.8%. SWs also showed different degrees of variability between individuals. Variability appeared to be higher in males than in females, possibly indicating differences in SW use in different social contexts. Furthermore, SWs with a greater level of frequency modulation varied more than less modulated whistles. We propose that SWs possess sufficient variation in their frequency contour to contain additional information, possibly related to social and behavioral context, while still maintaining their identity function.

Do marmosets really have names?

A recent study demonstrated that marmoset "phee calls" include information specific to the intended receiver of the call, and that receivers respond more to calls that are specifically directed at them. The authors interpret this as showing that these calls are name-like vocal labels for individual marmosets, but there is at least one other possibility that would equally explain these data.

The evolutionary path of the epithelial sodium channel δ-subunit in Cetartiodactyla points to a role in sodium sensing

The epithelial sodium channel (ENaC) plays a key role in osmoregulation in tetrapod vertebrates and is a candidate receptor for salt taste sensation. There are four ENaC subunits (α, β, γ, δ) which form αβγ- or δβγ ENaCs. While αβγ-ENaC is a 'maintenance protein' controlling sodium and potassium homeostasis, δβγ-ENaC might represent a 'stress protein' monitoring high sodium concentrations. The δ-subunit emerged with water-to-land transition of tetrapod vertebrate ancestors. We investigated the evolutionary path of ENaC-coding genes in Cetartiodactyla, a group comprising even-toed ungulates and the cetaceans (whales/dolphins) which transitioned from terrestrial to marine environments in the Eocene. The genes SCNN1A (α-ENaC), SCNN1B (β-ENaC) and SCNN1G (γ-ENaC) are intact in all 22 investigated cetartiodactylan families. While SCNN1D (δ-ENaC) is intact in terrestrial Artiodactyla, it is a pseudogene in 12 cetacean families. A fusion of SCNN1D exons 11 and 12 under preservation of the open reading frame was observed in the Antilopinae, representing a new feature of this clade. Transcripts of SCNN1A, SCNN1B and SCNN1G were present in kidney and lung tissues of Bottlenose dolphins, highlighting αβγ-ENaC's role as a maintenance protein. Consistent with SCNN1D loss, Bottlenose dolphins and Beluga whales did not show behavioural differences to stimuli with or without sodium in seawater-equivalent concentrations. These data suggest a function of δ-ENaC as a sodium sensing protein which might have become obsolete in cetaceans after the migration to high-salinity marine environments. Consistently, there is reduced selection pressure or pseudogenisation of SCNN1D in other marine mammals, including sirenians, pinnipeds and sea otter.

The Cetacean Sanctuary: A Sea of Unknowns

Housing cetaceans in netted sea pens is not new and is common for many accredited managed-care facilities. Hence, the distinction between sanctuary and sea pen is more about the philosophies of those who run these sanctuary facilities, the effects of these philosophies on the animals' welfare, and how proponents of these sanctuaries fund the care of these animals. Here, I consider what plans exist for cetacean sanctuaries and discuss the caveats and challenges associated with this form of activist-managed captivity. One goal for stakeholders should be to disregard the emotional connotations of the word "sanctuary" and explore these proposals objectively with the best interest of the animals in mind. Another focus should be related to gauging the public's understanding of proposed welfare benefits to determine if long-term supporters of donation-based sanctuary models will likely see their expectations met as NGOs and their government partners consider moving forward with cetacean sanctuary experiments.

First acoustic evidence of signature whistle production by spinner dolphins (Stenella longirostris)

A dolphin's signature whistle (SW) is a distinctive acoustic signal, issued in a bout pattern of unique frequency modulation contours; it allows individuals belonging to a given group to recognize each other and, consequently, to maintain contact and cohesion. The current study is the first scientific evidence that spinner dolphins (Stenella longirostris) produce SWs. Acoustic data were recorded at a shallow rest bay called "Biboca", in Fernando de Noronha Archipelago, Brazil. In total, 1902 whistles were analyzed; 40% (753/1,902) of them were classified as stereotyped whistles (STW). Based on the SIGID method, 63% (472/753) of all STWs were identified as SWs; subsequently, they were categorized into one of 18 SW types. SWs accounted for 25% (472/1,902) of the acoustic repertoire. External observers have shown near perfect agreement to classify whistles into the adopted SW categorization. Most acoustic and temporal variables measured for SWs showed mean values similar to those recorded in other studies with spinner dolphins, whose authors did not differentiate SWs from non-SWs. Principal component analysis has explained 78% of total SW variance, and it emphasized the relevance of shape/contour and frequency variables to SW variance. This scientific discovery helps improving bioacoustics knowledge about the investigated species. Future studies to be conducted in Fernando de Noronha Archipelago should focus on continuous investigations about SW development and use by S. longirostris, expanding individuals' identifications (Photo ID and SW Noronha Catalog), assessing long-term whistle stability and emission rates, and making mother-offspring comparisons with sex-based differences.

Bottlenose dolphins are sensitive to human attentional features, including eye functionality

The ability to attribute attentional states to other individuals is a highly adaptive socio-cognitive skill and thus may have evolved in many social species. However, whilst humans excel in this ability, even chimpanzees appear to not accurately understand how visual attention works, particularly in regard to the function of eyes. The complex socio-ecological background and socio-cognitive skill-set of bottlenose dolphins (Tursiops sp.), alongside the specialised training that captive dolphins typically undergo, make them an especially relevant candidate for an investigation into their sensitivity to human attentional states. Therefore, we tested 8 bottlenose dolphins on an object retrieval task. The dolphins were instructed to fetch an object by a trainer under various attentional state conditions involving the trainer's eyes and face orientation: 'not looking', 'half looking', 'eyes open', and 'eyes closed'. As the dolphins showed an increased latency to retrieve the object in conditions where the trainer's head and eyes cued a lack of attention to the dolphin, particularly when comparing 'eyes open' vs 'eyes closed' conditions, we demonstrate that dolphins can be sensitive to human attentional features, namely the functionality of eyes. This study supports growing evidence that dolphins possess highly complex cognitive abilities, particularly those in the social domain.

Bottlenose dolphin mothers modify signature whistles in the presence of their own calves

Human caregivers interacting with children typically modify their speech in ways that promote attention, bonding, and language acquisition. Although this "motherese," or child-directed communication (CDC), occurs in a variety of human cultures, evidence among nonhuman species is very rare. We looked for its occurrence in a nonhuman mammalian species with long-term mother-offspring bonds that is capable of vocal production learning, the bottlenose dolphin (Tursiops truncatus). Dolphin signature whistles provide a unique opportunity to test for CDC in nonhuman animals, because we are able to quantify changes in the same vocalizations produced in the presence or absence of calves. We analyzed recordings made during brief catch-and-release events of wild bottlenose dolphins in waters near Sarasota Bay, Florida, United States, and found that females produced signature whistles with significantly higher maximum frequencies and wider frequency ranges when they were recorded with their own dependent calves vs. not with them. These differences align with the higher fundamental frequencies and wider pitch ranges seen in human CDC. Our results provide evidence in a nonhuman mammal for changes in the same vocalizations when produced in the presence vs. absence of offspring, and thus strongly support convergent evolution of motherese, or CDC, in bottlenose dolphins. CDC may function to enhance attention, bonding, and vocal learning in dolphin calves, as it does in human children. Our data add to the growing body of evidence that dolphins provide a powerful animal model for studying the evolution of vocal learning and language.

A Quieter Ocean: Experimentally Derived Differences in Attentive Responses of Tursiops truncatus to Anthropogenic Noise Playbacks before and during the COVID-19-Related Anthropause

The effects of anthropogenic noise continue to threaten marine fauna, yet the impacts of human-produced sound on the broad aspects of cognition in marine mammals remain relatively understudied. The shutdown of non-essential activities due to the COVID-19-related anthropause created an opportunity to determine if reducing levels of oceanic anthropogenic noise on cetaceans affected processes of sensitization and habituation for common human-made sounds in an experimental setting. Dolphins at Dolphin Quest Bermuda were presented with three noises related to human activities (cruise ship, personal watercraft, and Navy low-frequency active sonar) both in 2018 and again during the anthropause in 2021 via an underwater speaker. We found that decreased anthropogenic noise levels altered dolphin responses to noise playbacks. The dolphins spent significantly more time looking towards the playback source, but less time producing burst pulse and echolocation bouts in 2021. The dolphins looked towards the cruise ship sound source significantly more in 2021 than 2018. These data highlight that different sounds may incur different habituation and sensitization profiles and suggest that pauses in anthropogenic noise production may affect future responses to noise stimuli as dolphins dishabituate to sounds over time.

Open questions in marine mammal sensory research

Although much research has focused on marine mammal sensory systems over the last several decades, we still lack basic knowledge for many of the species within this diverse group of animals. Our conference workshop allowed all participants to present recent developments in the field and culminated in discussions on current knowledge gaps. This report summarizes open questions regarding marine mammal sensory ecology and will hopefully serve as a platform for future research.

Multimodal imitative learning and synchrony in cetaceans: A model for speech and singing evolution

Multimodal imitation of actions, gestures and vocal production is a hallmark of the evolution of human communication, as both, vocal learning and visual-gestural imitation, were crucial factors that facilitated the evolution of speech and singing. Comparative evidence has revealed that humans are an odd case in this respect, as the case for multimodal imitation is barely documented in non-human animals. While there is evidence of vocal learning in birds and in mammals like bats, elephants and marine mammals, evidence in both domains, vocal and gestural, exists for two Psittacine birds (budgerigars and grey parrots) and cetaceans only. Moreover, it draws attention to the apparent absence of vocal imitation (with just a few cases reported for vocal fold control in an orangutan and a gorilla and a prolonged development of vocal plasticity in marmosets) and even for imitation of intransitive actions (not object related) in monkeys and apes in the wild. Even after training, the evidence for productive or "true imitation" (copy of a novel behavior, i.e., not pre-existent in the observer's behavioral repertoire) in both domains is scarce. Here we review the evidence of multimodal imitation in cetaceans, one of the few living mammalian species that have been reported to display multimodal imitative learning besides humans, and their role in sociality, communication and group cultures. We propose that cetacean multimodal imitation was acquired in parallel with the evolution and development of behavioral synchrony and multimodal organization of sensorimotor information, supporting volitional motor control of their vocal system and audio-echoic-visual voices, body posture and movement integration.

Social and vocal complexity in bottlenose dolphins

Bottlenose dolphins are highly social, renowned for their vocal flexibility, and possess highly enlarged brains relative to their body size. Here, we discuss some of the defining features of bottlenose dolphin social and vocal complexity and place this in the context of their cognitive evolution.

Understanding across the senses: cross-modal studies of cognition in cetaceans

Cross-modal approaches to the study of sensory perception, social recognition, cognition, and mental representation have proved fruitful in humans as well as in a variety of other species including toothed whales in revealing equivalencies that suggest that different sensory stimuli associated with objects or individuals may effectively evoke mental representations that are, respectively, object based or individual based. Building on established findings of structural equivalence in the form of spontaneous recognition of complex shapes across the modalities of echolocation and vision and behavior favoring identity echoic-visual cross-modal relationships over associative echoic-visual cross-modal relationships, examinations of transitive inference equivalencies from initially learned associations of visual and acoustic stimuli, and recent work examining spontaneous cross-modal social recognition of individual identity across acoustic and gustatory chemical modalities (i.e., the equivalence relationships among an individual's characteristics), we examine the history, utility and implications for cross-modal research in cetacean cognition. Drawing from research findings on bottlenose dolphins and beluga whales as well as other species we suggest future directions for cetacean cross-modal research to further illuminate understanding how structural and individual sensory equivalencies lead to object-centered and individual-centered mental representations, as well as to explore the potential for practical applications related to cetacean conservation.