Agonistic Vocalizations Research Articles

Enjoy the silence: Preference and short-term effect of exposure to different acoustical stimuli in dogs

Prior research has demonstrated that animal vocalizations and music can elicit emotional responses in dogs, but their preferences for different acoustic stimuli remain underexplored. This study aimed to develop a methodology to assess dogs’ preferences and behavioral reactions to various acoustic stimuli and examine the role of familiarity in shaping these responses. In the first experiment, 90 pet dogs were exposed to one of six types of sound stimuli: conspecific agonistic vocalizations, conspecific vocalizations recorded in positive contexts, classical music, relaxing music, dog-directed speech, and neutral background noise. The setup involved a room virtually divided into two areas, in which the dog could freely move. Sounds were turned on or off, depending on which of the two zones the dog was in, thereby giving subjects the possibility to choose whether to be exposed to the sound or not. Preferences were determined by relative amount of time spent in the sound versus quiet zone and behaviors were analyzed for emotional indicators. Dogs actively avoided agonistic vocalizations exhibiting increased attention-seeking behaviors toward their owners. No distinct preferences or aversions emerged for the other stimuli, although conspecific vocalizations in positive contexts and dog-directed speech elicited dogs’ attention. Both types of music resulted in lower attention towards the sound compared to the neutral condition. In Experiment 2, the same procedure was used with 20 dogs, half of whom were routinely exposed to classical music at home, to test whether familiarity with classical music affected behavioral responses and preferences. Although no significant behavioral changes or preferences for classical music were observed, dogs with prior exposure spent twice as much time in the sound zone compared to those without, suggesting enhanced likability due to familiarity. These dogs also exhibited more relaxed behaviors, indicating that familiarity may influence emotional responses.Overall, the study introduces a novel approach for evaluating dogs' preferences for acoustic stimuli. It revealed that none of the stimuli allegedly inducing positive emotions led to a clear preference. However, behavioral data suggest that familiarity can enhance the likability of specific sounds. These findings highlight the need for further investigation into how different soundscapes influence dogs' emotions and behavior over time, and whether dogs may inherently prefer silence. Moreover, the results underscore the importance of carefully considering acoustic enrichment strategies, particularly the role of familiarization in shaping dogs' responses to their auditory environment.

Cerebral Activity in Female Baboons (Papio anubis) During the Perception of Conspecific and Heterospecific Agonistic Vocalizations: a Functional Near Infrared Spectroscopy Study

The “voice areas” in the superior temporal cortex have been identified in both humans and non-human primates as selective to conspecific vocalizations only (i.e., expressed by members of our own species), suggesting its old evolutionary roots across the primate lineage. With respect to non-human primate species, it remains unclear whether the listening of vocal emotions from conspecifics leads to similar or different cerebral activations when compared to heterospecific calls (i.e., expressed by another primate species) triggered by the same emotion. Using a neuroimaging technique rarely employed in monkeys so far, functional Near Infrared Spectroscopy, the present study investigated in three lightly anesthetized female baboons (Papio anubis), temporal cortex activities during exposure to agonistic vocalizations from conspecifics and from other primates (chimpanzees—Pan troglodytes), and energy matched white noises in order to control for this low-level acoustic feature. Permutation test analyses on the extracted OxyHemoglobin signal revealed great inter-individual differences on how conspecific and heterospecific vocal stimuli were processed in baboon brains with a cortical response recorded either in the right or the left temporal cortex. No difference was found between emotional vocalizations and their energy-matched white noises. Despite the phylogenetic gap between Homo sapiens and African monkeys, modern humans and baboons both showed a highly heterogeneous brain process for the perception of vocal and emotional stimuli. The results of this study do not exclude that old evolutionary mechanisms for vocal emotional processing may be shared and inherited from our common ancestor.

Agonistic vocalization behaviour in the male ring-tailed lemur (Lemur catta).

Vocalizations are used by group-living animals as aggressive and submissive signals during agonistic interactions, and are also used to maintain dominance hierarchies in many species. For gregarious strepsirrhines with large vocal repertoires and differentiated dominance ranks like the ring-tailed lemur (Lemur catta), agonistic vocalization use is important to study to better understand their social adaptations.To determine whether ring-tailed lemur vocalizations such as the yip, cackle, twitter, chutter, and plosive bark were used as aggressive or submissive signals during agonism and uttered at different rates by males of differing dominance ranks and ages, 565 h of focal data were collected on 31 individual males aged ≥ 1 year from Beza Mahafaly Special Reserve, Madagascar. Yip, cackle, and twitter vocalizations were consistently used during agonistic submissive interactions with both males and females, chutter vocalizations were used during aggressive agonistic interactions with males and submissive agonistic interactions with males and females, and plosive bark vocalizations were used across behavioural contexts but not particularly during agonism. Males of all ages employed all vocalizations, and while low-ranking males uttered yip calls at higher rates, males of all dominance ranks uttered cackle, twitter, chutter, and plosive bark vocalizations. These results advance our knowledge of how male lemurs utilize agonistic vocalizations to maintain inter-individual relationships with males and females, and improve our overall understanding of the function of different agonistic vocalizations in wild lemurs.

A green racer snake (Philodryas nattereri, Colubridae) killed but not eaten by a blonde capuchin monkey (Sapajus flavius, Cebidae).

We report the killing of a snake (Philodryas nattereri, Colubridae) by a blonde capuchin monkey (Sapajus flavius, Cebidae). This endemic primate species from the northeast of Brazil includes vertebrates such as lizards and marsupials in its diet, but we can find no previously published record of an attack upon or consumption of snakes by this species of platyrhine monkey. During the attack, the group mobbed the snake, with individuals uttering agonistic vocalizations and displaying behaviors such as raising their tails, moving tree branches, piloerecting, and baring their teeth. An adult male monkey seized the snake, bit and twisted its body, thereby killing it; he then dropped the carcass onto tree branches, but did not consume it. This single event suggests that this Cebidae species may be able to distinguish dangerous from harmless snakes, and it also may be an example of a lethally violent reaction to a potential predator or competitor, exemplifying the plasticity and cognitive skills exhibited by genus Sapajus.

Agonism Management Through Agonistic Vocal Signaling in Subterranean Rodents: A Neglected Factor Facilitating Sociality?

Communication is inherent to social relationships. Previous papers addressed the correlation between social and communicative complexity, and the origin of sociality in rodents. In subterranean social species, as the number of animals in the same burrow increases, so do interindividual contact rates. This is because of limitations in actually used tunnel length and diameter, leading to an increasing number of agonistic situations probably resulting in time loss, threatening, and fighting with danger of injuries. To avoid this, social species are expected to have an increase in the number of particular vocalizations. Comparison of the adult vocal repertoire of 12 species (seven genera) through regression and phylogenetically independent contrasts (PIC) suggests three main conclusions: (1) social species increase their repertoire both in number and categories of vocal signals in relation to solitary species, although the coefficient was smaller in the PIC model; (2) the number of agonistic vocalizations was also different between solitary and social species, with the latter displaying higher numbers of these calls; (3) the percentage of agonistic vocalizations in relation to total repertoire was similar between social and solitary species, with no significant relationship between this parameter and the social structure. These results imply that agonistic vocalizations have also increased in number in social species, indicating the importance of these calls in the establishment of new relationships. As repertoire changes are essential to cope with new and frequent kinds of interactions sociality originates, these results suggest that at least for these organisms, communicative changes, especially at the level of agonistic signals, could be a necessary condition to fulfill in the path to the possibility of group living.

Vocal Repertoire and Its Behavioral Contexts in the Pied Tamarin, Saguinus bicolor

The study of animal sound signals can be useful in assisting conservation strategies. Understanding the vocal repertoires of endangered species and the behavioral contexts in which they are given is relevant for monitoring protocols, such as those based on automated sound recordings. The pied tamarin (Saguinus bicolor) is at risk of extinction because of deforestation and urban growth in its restricted geographic range. Between 2012 and 2015 we studied the vocal repertoire of the species and the contexts in which different signals are emitted. We made focal recordings of eight free-living groups, two rescued individuals, and one temporarily captive group of pied tamarins in Manaus, central Brazilian Amazonia. From the 766 sounds analyzed we identified 12 distinct signals within the range of 2–11 kHz. Most signals were emitted during resting or locomotion. Less frequently emitted signals were associated with intergroup agonistic interactions, foraging, and infant-exclusive vocalizations. These results increased the known vocal repertoire of the pied tamarin providing more reliable baseline data for monitoring the species by means of automated or focal sound recordings.

Threat-level-dependent manipulation of signaled body size: dog growls' indexical cues depend on the different levels of potential danger.

Body size is an important feature that affects fighting ability; however, size-related parameters of agonistic vocalizations are difficult to manipulate because of anatomical constraints within the vocal production system. Rare examples of acoustic size modulation are due to specific features that enable the sender to steadily communicate exaggerated body size. However, one could argue that it would be more adaptive if senders could adjust their signaling behavior to the fighting potential of their actual opponent. So far there has been no experimental evidence for this possibility. We tested this hypothesis by exposing family dogs (Canis familiaris) to humans with potentially different fighting ability. In a within-subject experiment, 64 dogs of various breeds consecutively faced two threateningly approaching humans, either two men or two women of different stature, or a man and a woman of similar or different stature. We found that the dogs' vocal responses were affected by the gender of the threatening stranger and the dog owner's gender. Dogs with a female owner, or those dogs which came from a household where both genders were present, reacted with growls of lower values of the Pitch-Formant component (including deeper fundamental frequency and lower formant dispersion) to threatening men. Our results are the first to show that non-human animals react with dynamic alteration of acoustic parameters related to their individual indexical features (body size), depending on the level of threat in an agonistic encounter.

Acoustic characteristics of courtship and agonistic vocalizations in Przwewalskii's wild horse and in domestic horse

For closely related species living in similar habitats, differences in the acoustic morphology of vocalizations could play a role in mate recognition as well as provide insight into the evolutionary divergence between species. Przwewalski's horses (Equus Przwewalskii) and Mongolian domestic horses (Equus callabus) are sometimes found cohabiting in the same environment during the mating season. As such, we examined the hypothesis that interspecies differences are reflected in the acoustic morphology of vocalizations produced by two closely related species.We analyzed the acoustic structure of courtship nickers and agonistic squeals produced by Przwewalski's and Mongolian domestic stallions. Our acoustic analyses indicated that agonistic squeals produced by Przwewalski's stallions were significantly higher in source-related acoustic parameters and in the frequency of maximal energy than those produced by Mongolian domestic stallions. In addition to species differences, we found context-related differences in Przwewalski's stallion vocalizations. Courtship nickers were significantly lower in fundamental frequencies than agonistic squeals.Our findings suggest that acoustic differences between nickers and squeals could reflect underlying motivational states in Przwewalski's horses. Interspecies differences in acoustic structure however, are restricted to agonistic squeals. From an evolutionary standpoint, the lack of interspecies differences in courtship vocalizations suggest that similar factors influence the evolution of courtship calls whereas the differences found in agonistic vocalizations indicate that different factors modulate the evolution of agonistic calls.

Role of Emitter and Severity of Aggression Influence the Agonistic Vocalizations of Geoffroy’s Spider Monkeys (Ateles geoffroyi)

Natural selection has resulted in the acoustic convergence of many animal vocalizations. During agonistic interactions vocalizations may vary depending on the role an individual plays in the interaction and on the severity of the attack. Motivation-structural rules describe how aggressors are thought to have evolved to use low-frequency vocalizations, whereas victims often use high-frequency vocalizations. This is because call frequency (Hz) is negatively related to body size across species. Motivational theory predicts that during more severe attacks, vocal structure will also change in response to increased arousal, leading to the production of noisy (high-entropy) vocalizations. Little is known about the acoustic characteristics of vocalizations produced during agonistic encounters in primates, and the limited available data are highly biased toward Old World species. Here, we evaluated the effect of the role of the emitter (aggressor or victim) and the severity of the behavior (with or without contact) on the acoustic parameters of 185 agonistic vocalizations emitted by 15 spider monkeys (Ateles geoffroyi) in two captive groups. Our results supported the predictions of both the motivation-structural rules and motivational theory: Call frequency (Hz) was lower in aggressors than in victims and lower during high-severity encounters than low-severity encounters. Further, average entropy was higher during high-severity encounters. These findings suggest that the agonistic vocalizations of spider monkeys convey information about both the role of the emitter and the severity of the interaction.

Stimulation of the basal and central amygdala in the mustached bat triggers echolocation and agonistic vocalizations within multimodal output

The neural substrate for the perception of vocalizations is relatively well described, but how their timing and specificity are tightly coupled with accompanying physiological changes and context-appropriate behaviors remains unresolved. We hypothesized that temporally integrated vocal and emotive responses, especially the expression of fear, vigilance and aggression, originate within the amygdala. To test this hypothesis, we performed electrical microstimulation at 461 highly restricted loci within the basal and central amygdala in awake mustached bats. At a subset of these sites, high frequency stimulation with weak constant current pulses presented at near-threshold levels triggered vocalization of either echolocation pulses or social calls. At the vast majority of locations, microstimulation produced a constellation of changes in autonomic and somatomotor outputs. These changes included widespread co-activation of significant tachycardia and hyperventilation and/or rhythmic ear pinna movements (PMs). In a few locations, responses were constrained to vocalization and/or PMs despite increases in the intensity of stimulation. The probability of eliciting echolocation pulses vs. social calls decreased in a medial-posterior to anterolateral direction within the centrobasal amygdala. Microinjections of kainic acid (KA) at stimulation sites confirmed the contribution of cellular activity rather than fibers-of-passage in the control of multimodal outputs. The results suggest that localized clusters of neurons may simultaneously modulate the activity of multiple central pattern generators (CPGs) present within the brainstem.

Ontogenesis of agonistic vocalizations in the cichlid fish Metriaclima zebra

While acoustic communication has been described in adults of various fish species, our knowledge about the ontogeny of fish sound production is limited. In adults, sound signals are known to be involved during aggressive interactions. However, aggressive behaviour may appear early in the life of fishes due to the possible competition for food and space. If acoustic signals are used to send information to competitors, sounds are likely to play a role during interactions between juvenile fish as well. The apparition and evolution of sound production were monitored in a group of juveniles of the cichlid fish Metriaclima zebra from hatching to 4months of age. In addition, the link between vocalizations and agonistic behaviour was studied during dyadic interactions at three different ages. Sounds production appeared to be present early in the development of this fish and increased along with the number of aggressive behaviours. Recorded sounds consisted, in juveniles, in isolated pulses showing a decrease in frequency and duration as the fish grew. In adults, sounds became bursts of pulses but the transition from isolated to repetitive pulses was not observed. These results are compared to the existing literature on sound production ontogeny in fishes.

RNA Interference of Gonadotropin-Inhibitory Hormone Gene Induces Arousal in Songbirds

Gonadotropin-inhibitory hormone (GnIH) was originally identified in quail as a hypothalamic neuropeptide inhibitor of pituitary gonadotropin synthesis and release. However, GnIH neuronal fibers do not only terminate in the median eminence to control anterior pituitary function but also extend widely in the brain, suggesting it has multiple roles in the regulation of behavior. To identify the role of GnIH neurons in the regulation of behavior, we investigated the effect of RNA interference (RNAi) of the GnIH gene on the behavior of white-crowned sparrows, a highly social songbird species. Administration of small interfering RNA against GnIH precursor mRNA into the third ventricle of male and female birds reduced resting time, spontaneous production of complex vocalizations, and stimulated brief agonistic vocalizations. GnIH RNAi further enhanced song production of short duration in male birds when they were challenged by playbacks of novel male songs. These behaviors resembled those of breeding birds during territorial defense. The overall results suggest that GnIH gene silencing induces arousal. In addition, the activities of male and female birds were negatively correlated with GnIH mRNA expression in the paraventricular nucleus. Density of GnIH neuronal fibers in the ventral tegmental area was decreased by GnIH RNAi treatment in female birds, and the number of gonadotropin-releasing hormone neurons that received close appositions of GnIH neuronal fiber terminals was negatively correlated with the activity of male birds. In summary, GnIH may decrease arousal level resulting in the inhibition of specific motivated behavior such as in reproductive contexts.

‘The bone is mine’: affective and referential aspects of dog growls

A number of species are considered to use functionally referential signals such as alarm calls or food-related vocalizations. However, this particular function of communicative interaction has not previously been found in canids. We provide the first experimental indication that domestic dogs, Canis familiaris, rely on context-dependent signals during interspecific agonistic encounters. We recorded several sequences of growls from dogs in three different contexts: during play, guarding a bone from another dog, and reacting to a threatening stranger. We analysed the acoustic structure of the growls and additionally performed playback tests in a seminatural food-guarding situation. We found that play growls differed acoustically from the other two (agonistic) types of growls, mainly in their fundamental frequencies and formant dispersions. Results of the playback experiment showed that food-guarding growls deterred other dogs from taking away a seemingly unattended bone more effectively than growls recorded in the threatening stranger situation. We ruled out an effect of the signaller's body weight on the subjects' responses. These results provide the first evidence of context specificity of agonistic vocalizations in the dog. We discuss the possible aspects of honesty and deception through acoustic modulation of growls.

Neighbor effects in marmosets: social contagion of agonism and affiliation in captive Callithrix jacchus

Researchers have demonstrated the neighbor effect for affiliative and agonistic neighbor vocalizations in captive chimpanzees. We extend the investigation of the neighbor effect to New World monkeys, Callithrix jacchus. We collected data on vocalizations and behaviors of 31 focal individuals and concurrent neighbor vocalization within three behavioral categories: intragroup and intergroup aggression and intragroup affiliation. We investigated whether there was an influence of neighbor vocalizations on focal behavior within the same behavioral category. For data analysis we used approximate randomization of paired-sample t-tests. We found that marmosets performed intergroup aggressive behavior (bristle, anogenital present for neighbor loud shrill only) for significantly longer, and emitted significantly more intergroup agonistic vocalizations (twitter, loud shrill), at a high frequency of intergroup agonistic neighbor vocalizations (twitter, loud shrill) than at low. The marmosets were also significantly more likely to engage in bristle behavior immediately after hearing a neighbor intergroup aggressive call (twitter, loud shrill) than directly beforehand. High neighbor intragroup agonistic calls (chatter) were associated with significantly longer spent in related behavior (composite of: attack, chase, steal food). Affiliative behaviors (share food, grooming invite) were engaged in by marmosets for significantly longer at higher frequencies of affiliative neighbor chirp calls than at low. Marmosets were also significantly more likely to perform food sharing and active affiliative contact immediately after rather than before hearing a neighbor chirp call. Our findings suggest that neighbor vocalizations influence marmoset behavior through social contagion and indicate that the neighbor effect for affiliation and aggression generalizes to the marmoset.

First documentation of spawning and nest guarding in the laboratory by the invasive fish, the round goby ( Neogobius melanostomus)

Although the round goby, Neogobius melanostomus, is widespread in the Great Lakes and has an extended breeding season with a high reproductive rate; its spawning behaviour remains elusive. We present the first reported accounts of spawning by the round goby in the laboratory. By simulating winter conditions and restoring spring conditions, we induced round gobies to spawn in October 2007, March 2008, May 2008, and January 2009. In one case, fanning by the nest-holding male began 10 days before egg deposition and, during this period, the male rubbed secretions along the ceiling of the nest. Males were choosy about which gravid females entered the nest and prevented entry by some females. Spawning involved repeated inversions by females and males releasing gametes on the ceiling of the nest. Males guarded the nest by blocking the entrance, producing agonistic vocalizations and chasing intruders. Inside the nest, eggs were regularly inspected by the males and constantly ventilated using pectoral and caudal fins. Up to three gravid females spawned sequentially in a nest. Peak ventilation occurred after egg deposition and declined with time until the parental male ate the eggs. The decline of parental care and egg cannibalism was likely an artifact of laboratory conditions and small brood size. Our findings offer new information on the reproductive habits of the invasive round goby. Because the reproductive sequence in the laboratory seems easy to disrupt, the procedures may lead to a management tool to control the spread of the species into new areas.

Development of vocalization, auditory sensitivity and acoustic communication in the Lusitanian toadfishHalobatrachus didactylus

The ontogenetic development of acoustic communication has so far only been investigated in one fish species. In order to determine whether detectability of conspecific sounds changes during growth in a species with limited hearing abilities (generalist), we investigated the development of auditory sensitivity and agonistic vocalizations in the Lusitanian toadfish Halobatrachus didactylus. Agonistic grunts were recorded, their sound pressure levels determined, and auditory sensitivities measured in five different size groups ranging from 3 to 32 cm standard length. Hearing thresholds were obtained using the auditory evoked potentials (AEP) recording technique. Dominant frequency, sound duration and number of pulses decreased, whereas pulse period and sound level increased with increasing fish size. The best hearing was below 300 Hz in all groups. Lower hearing sensitivity was found in the smallest juveniles at 100 Hz as well as at higher frequencies (800 and 1000 Hz). Comparisons between audiograms and sound spectra within the same-sized fish revealed that smaller juveniles would be barely able to detect agonistic grunts, while these vocalizations were clearly perceived by larger fish. In the latter, the main energy of sounds was found at the most sensitive frequencies. This study demonstrates that acoustic communication in the Lusitanian toadfish might be absent in early developmental stages and seems to start when juveniles are able to generate grunts of higher sound level and lower dominant frequency.

Effects of ship noise on the detectability of communication signals in the Lusitanian toadfish

Underwater noise pollution is an increasing environmental problem which might affect communication, behaviour, fitness and consequently species' survival. The most common anthropogenic noises in aquatic habitats derive from shipping. In the present study we investigated the implications of noise pollution from a ship on the sound detectability, namely of conspecific vocalizations in the Lusitanian toadfish, Halobatrachus didactylus. Ambient and ferry-boat noises were recorded in the Tagus River estuary (Portugal), as well as toadfish sounds, and their sound pressure levels determined. Hearing sensitivities were measured under quiet lab conditions and in the presence of these masking noises at levels encountered in the field, using the auditory evoked potentials (AEP) recording technique. The Lusitanian toadfish is a hearing generalist, with best hearing sensitivity at low frequencies between 50 and 200 Hz (below 100 dB re. 1 microPa). Under ambient noise conditions, hearing was only slightly masked at lower frequencies. In the presence of ship noise, auditory thresholds increased considerably, by up to 36 dB, at most frequencies tested. This is mainly because the main energies of ferry-boat noise were within the most sensitive hearing range of this species. Comparisons between masked audiograms and sound spectra of the toadfish's mating and agonistic vocalizations revealed that ship noise decreased the ability to detect conspecific acoustic signals. This study provides the first evidence that fishes' auditory sensitivity can be impaired by ship noise and that acoustic communication, which is essential during agonistic encounters and mate attraction, might be restricted in coastal environments altered by human activity.

Observational Evidences of Vocal Learning in Southern Elephant Seals: a Longitudinal Study

AbstractVocal learning in mammals is sparsely documented, and there are few reports of vocal learning by wild mammals. In particular, no information based on longitudinal data for identified individuals exists, even for well‐studied highly social species in which vocal communication is an important aspect of social life. We present such information for the southern elephant seal (Mirounga leonina). We studied a small breeding population in the Falkland Islands over 8 yr (1995–2002). We recorded approx. 2400 agonistic vocalizations from approx. 285 different males, including many recorded over more than one breeding season (55 males were recorded for >2 yr and 29 were recorded throughout vocal development). Vocalizations are a key element of male agonistic behaviour in this species, the world's most polygynous vertebrate. For male agonistic vocalizations, we show that: (1) a limited number of discrete vocal types exists; (2) proportions of vocal types change over time; (3) observed trends of increase or decrease of vocal types are well explained by a process of vocal learning, in which younger peripheral males imitate vocal types of older more successful breeders.

Having a big nose: structure, ontogeny, and function of the elephant seal proboscis

The proboscis of male elephant seals ( Mirounga Gray, 1827) has been suggested as an example of a secondary sexual trait since Darwin. There has been much speculation about its social function (e.g., optical signal of breeding status, amplification of vocalizations, cue for female choice). However, it has never been studied in detail, probably because its fleshy nature makes measurement difficult. In this paper, we employ photogrammetry to measure the proboscis and facial morphology of a large sample of wild, unrestrained, displaying male southern elephant seals ( Mirounga leonina (L., 1758)). We describe ontogeny and allometry of the proboscis and analyze current phenotypic selection pressures on proboscis traits. We discuss the potential role of the proboscis in optical and acoustic signaling of male resource-holding potential and status. We demonstrate that proboscis size is positively correlated with age and body size independently, and that it is currently under a positive sexual selection pressure when the effect of selection on body size is removed. We suggest that selection on proboscis size is functionally related to the emission of agonistic vocalizations.

Vocal signalling of male southern elephant seals is honest but imprecise

In the most common models of communication, it is assumed that animals provide reliable information about phenotype, and hence can settle competitive contests without physical interactions like fights. This assumption has rarely been tested for wild mammals. Recent studies of mammals have revealed relationships of vocal attributes to age and body size. Here, we analyse relationships of frequency attributes of agonistic vocalizations to phenotype (age, body size, proboscis size and agonistic behaviour) in males of the southern elephant seal, Mirounga leonina, a species with intense male competition for access to females, and in which vocalizations are used frequently to settle male–male contests. We analysed formant structure and vocal tract size, and found that nasal and oral components of the vocal tract contribute separately to vocal formants; hence, the male's proboscis serves to elongate the vocal tract. We also found that formants in the upper part of the frequency spectrum (fourth and fifth in particular) and formant dispersion convey significant information about age, size and resource holding potential at large, and, therefore, can be honest signals of a vocalizer's phenotype. Explained variance was statistically significant in our study and in similar studies but was not high, so formant structure cannot serve as the sole basis of acoustic assessment. Other possible sources of information exchanged in elephant seal contests are nonvocal acoustic signals (e.g. vibrations) and optical displays.