Call combination patterns in Icelandic killer whales (Orcinus orca)

Acoustic sequences have been described in a range of species and in varying complexity. Cetaceans are known to produce complex song displays but these are generally limited to mysticetes; little is known about call combinations in odontocetes. Here we investigate call combinations produced by killer whales (Orcinus orca), a highly social and vocal species. Using acoustic recordings from 22 multisensor tags, we use a first order Markov model to show that transitions between call types or subtypes were significantly different from random, with repetitions and specific call combinations occurring more often than expected by chance. The mixed call combinations were composed of two or three calls and were part of three call combination clusters. Call combinations were recorded over several years, from different individuals, and several social clusters. The most common call combination cluster consisted of six call (sub-)types. Although different combinations were generated, there were clear rules regarding which were the first and last call types produced, and combinations were highly stereotyped. Two of the three call combination clusters were produced outside of feeding contexts, but their function remains unclear and further research is required to determine possible functions and whether these combinations could be behaviour- or group-specific.

Sensory integration of danger and safety cues may explain the fear of a quiet coyote

Sensory integration theory predicts natural selection should favour adaptive responses of animals to multiple forms of information, yet empirical tests of this prediction are rare, particularly in free-living mammals. Studying indirect predator cues offers a salient opportunity to inquire about multimodal risk assessment and its potentially interactive effects on prey responses. Here we exposed California ground squirrels from two study sites (that differ in human and domestic dog activity) to acoustic and/or olfactory predator cues to reveal divergent patterns of signal dominance. Olfactory information most strongly predicted space use within the testing arena. That is, individuals, especially those at the human-impacted site, avoided coyote urine, a danger cue that may communicate the proximity of a coyote. By contrast, subjects allocated less time to risk-sensitive behaviours when exposed to acoustic cues. Specifically, although individuals were consistent in their behavioural responses across trials, 'quiet coyotes' (urine without calls) significantly increased the behavioural reactivity of prey, likely because coyotes rarely vocalize when hunting. More broadly, our findings highlight the need to consider the evolution of integrated fear responses and contribute to an emerging understanding of how animals integrate multiple forms of information to trade off between danger and safety cues in a changing world.

Alarm Calling in Plateau Pika (Ochotona curzoniae): Evidence from Field Observations and Simulated Predator and Playback Experiments

Acoustic communication plays a vital role in passing or sharing information between individuals. Identifying the biological meaning of vocal signals is crucial in understanding the survival strategies of animals. However, there are many challenges in identifying the true meaning of such signals. The plateau pika (Ochotona curzoniae) is a call-producing mammal endemic to the Qinghai-Tibet plateau (QTP) and considered a keystone species owing to its multiple benefits in alpine rangeland ecosystems. Previous studies have shown that plateau pikas emit alarm calls as part of their daily activities. However, only field observations have been used to identify these alarm calls of the plateau pika, with no attempts at using playback experiments. Here, we report the alarm calling of plateau pikas through field observations as well as simulated predator and playback experiments in the Eastern QTP from 2021 to 2022. We found that both female and male adults emitted alarm calls, the signals of which comprised only one syllable, with a duration of 0.1-0.3 s. There were no differences in the characteristics between the observed alarm calls and those made in response to the simulated predator. The duration of the alarm call response varied with altitude, with plateau pikas living at higher altitudes responding at shorter durations than those at lower altitudes.

Early life experience and sex influence acoustic repertoire use in wild-born, but hand-reared, captive cheetahs (Acinonyx jubatus)

Early deprivation of adult influence is known to have long-lasting effects on social abilities, notably communication skills, as adults play a key role in guiding and regulating the behavior of youngsters, including acoustic repertoire use in species in which vocal production is not learned. Cheetahs grow up alongside their mother for 18 months, thus maternal influences on the development of social skills are likely to be crucial. Here, we investigated the impact of early maternal deprivation on vocal production and use in 12 wild-born cheetahs, rescued and subsequently hand-reared either at an early (less than 2 months) or a later stage of development. We could distinguish 16 sound types, produced mostly singly but sometimes in repeated or multitype sound sequences. The repertoire of these cheetahs did not differ fundamentally from that described in other studies on adult cheetahs, but statistical analyses revealed a concurrent effect of both early experience and sex on repertoire use. More specifically, early-reared males were characterized by a high proportion of Purr, Meow, and Stutter; early-reared females Mew, Growl, Hoot, Sneeze, and Hiss; late-reared males Meow, Mew, Growl, and Howl; and late-reared females mostly Meow. Our study demonstrates therefore the long-term effects of maternal deprivation on communication skills in a limited-vocal learner and its differential effect according to sex, in line with known social differences and potential differential maternal investment. More generally, it emphasizes the critical importance to consider the past history of the subjects (e.g., captive/wild-born, mother/hand-reared, early/late-mother-deprived, etc.) when studying social behavior, notably acoustic communication.

Landscapes of Time: Building Long-Term Perspectives in Animal Behavior

In the 1960s, scientists fascinated by the behavior of free-living animals founded research projects that expanded into multi-generation investigations. This paper charts the history of three scientists' projects to uncover the varied reasons for investing in a "long-term" perspective when studying animal behavior: Kenneth Armitage's study of marmots in the Rocky Mountains, Jeanne Altmann's analysis of baboons in Kenya, and Timothy Hugh Clutton-Brock's studies (among others) of red deer on the island of Rhum and meerkats in the Kalahari. The desire to study the behavior of the same group of animals over extended periods of time, I argue, came from different methodological traditions - population biology, primatology, and sociobiology - even as each saw themselves as contributing to the legacy of ethology. As scientists embraced and combined these approaches, a small number of long-running behavioral ecology projects like these grew from short pilot projects into decades-long centers of intellectual gravity within behavioral ecology as a discipline. By attending to time as well as place, we can see how this long-term perspective was crucial to their success; they measured evolutionary changes over generations of animals and their data provided insights into how the animals they studied were adapting (or not) to changing local and global environmental factors.

Feel the beat: cape fur seal males encode their arousal state in their bark rate

The cape fur seal is one of the most colonial mammal species in the world. Breeding colonies are composed of harems held by mature males (older than 10 years) with up to 30 females and their pups, while roaming subadult males (younger and socially immature) are kept away from bulls' territories. As in other pinnipeds, cape fur seals are highly vocal and use acoustic signals in all their social interactions. Males produce barks-short vocalizations always produced in sequences-for territorial defense, mating behaviors, and agonistic interactions. These calls convey information about the sex, age class, and individual identity. This study investigated whether motivational cues such as the arousal state can be encoded in territorial males' barks and whether these cues are decoded by listening sub-adult males. The rate (number of calls per unit of time) and fundamental frequency of barks were found to significantly increase during high arousal state interactions (i.e., male-male confrontation) compared to spontaneous barks. Playback experiments revealed that subadult males responded with a higher level of vigilance when territorial males' barks had a faster bark rate. This mechanism of decoding the bulls' arousal state from barks will likely constitute an advantage for both bulls and the subadult males, by avoiding or reducing physical conflicts, and thereby reducing energy expenditure and the risk of injury. This study is the first experimental evidence of cape fur seals' using vocal rhythmic patterns to modulate their social interactions.

Non-stereotyped amplitude modulation across signature whistle contours

Bottlenose dolphin signature whistles are characterized by distinctive frequency modulation over time. The stable frequency contours of these whistles broadcast individual identity information. Little is known however, about whether or not the amplitude contour is also stereotyped. Here, we examined the relative amplitude-time contour of signature whistle emissions from eight bottlenose dolphins (Tursiops truncatus) in the U.S. Navy Marine Mammal Program (MMP) in San Diego, CA. The results suggested that unlike the stable frequency-time contour, the amplitude-time contour of signature whistles were largely non-stereotyped, characterized by large variability across multiple whistle emissions. Relative amplitude was negatively related to log peak frequency, with more energy focused in the lower frequency bands. This trend was consistent over all eight dolphins despite having quite different signature whistle contours. This relationship led to the amplitude contours being slightly more stereotyped within than between dolphins. We propose that amplitude across signature whistle emissions may serve as an avenue for encoding additional communicative information. We encourage future studies to incorporate analyses of amplitude contours in addition to frequency contours of signature whistles in order to begin to understand what role it may play in the dolphin communication system.

Giant hornet (Vespa soror) attacks trigger frenetic antipredator signalling in honeybee (Apis cerana) colonies

Asian honeybees use an impressive array of strategies to protect nests from hornet attacks, although little is understood about how antipredator signals coordinate defences. We compared vibroacoustic signalling and defensive responses of Apis cerana colonies that were attacked by either the group-hunting giant hornet Vespa soror or the smaller, solitary-hunting hornet Vespa velutina. Apis cerana colonies produced hisses, brief stop signals and longer pipes under hornet-free conditions. However, hornet-attack stimuli-and V. soror workers in particular-triggered dramatic increases in signalling rates within colonies. Soundscapes were cacophonous when V. soror predators were directly outside of nests, in part because of frenetic production of antipredator pipes, a previously undescribed signal. Antipredator pipes share acoustic traits with alarm shrieks, fear screams and panic calls of primates, birds and meerkats. Workers making antipredator pipes exposed their Nasonov gland, suggesting the potential for multimodal alarm signalling that warns nestmates about the presence of dangerous hornets and assembles workers for defence. Concurrent observations of nest entrances showed an increase in worker activities that support effective defences against giant hornets. Apis cerana workers flexibly employ a diverse alarm repertoire in response to attack attributes, mirroring features of sophisticated alarm calling in socially complex vertebrates.

The acoustic behavior of the Brazilian caatinga big rodent is incongruent to its actual position in Hydrochoerinae

Our knowledge about the acoustic behavior of Caviinae species drove us to investigate Kerodon rupestris's (Caviidae: Hydrochoerinae) repertoire. This species is endemic to Caatinga and states as vulnerable in the Brazilian list of endangered species. We recorded sounds uttered by individuals from Santa Luzia, State of Paraíba, Brazil. We promoted interactions among 13 animals during intra and intersexual pairing sessions, under undisturbed interactions in captivity, and in free-living conditions. We found a repertoire of 13 call types, most of them (all except three) shared with Cavia and only five possibly shared also with Hydrochoerus: (1) Close contact and cohesion: tonal and noisy contact calls, tweet, slow-whistle; (2) Social regulation (incitement, subordination or auto-defense): whine, peepy-squeak, yelp; (3) Offensive aggression and status display: roar, snort, and teeth-chattering (4) Warning or intimidation: alarm-whistle, drrr, and drumming; (5) Courtship: purr and slow-whistle. The similarity of Kerodon signals to Hydrochoerinae species, despite the ecological differences, needs to be understood in comparative phylogenetic studies tracing back the origin of the courtship display in Caviidae. Thus, future research should focus on playback studies to test signals' biological function hypothesis.

Daurian pika (Ochotona dauurica) alarm calls: individual acoustic variation in a lagomorph with audible through ultrasonic vocalizations

Colonial lagomorphs warn conspecifics of potential danger with alarm calls encoding information about attributes of presumptive predators as well as the caller. In this study, we show that alarm calls of Daurian pikas, Ochotona dauurica (Pallas, 1776), encode information about caller identity. We recorded the alarm calls produced toward a surrogate predator (researcher), slowly moving (0.5–1 km/h) between densely distributed colonies. The alarm calls of most (32 of the 35) callers started in the ultrasonic range at 22.41 kHz on average and rapidly decreased to 3.88 kHz on average at call end. Call duration was very short (0.057 s on average). The accuracy of classifying alarm calls to correct callers with discriminant function analysis (DFA) was 93.71% for the manually measured set of 12 acoustic variables and 95.43% for the semiautomatically measured set of 12 acoustic variables; in both cases exceeding the level of chance (17.28% or 17.33%, respectively). Nonlinear vocal phenomena (biphonations) only were detected in one individual. We discuss the relationship between vocal traits, individuality, vocal production mechanisms, and functions, of pika alarm calls. We propose a potential divergence of alarm calls in Asian pikas to high-frequency whistles (> 20 kHz in Daurian pikas) and in American pikas to low-frequency emissions (0.4–1.3 kHz in Ochotona princeps) during the evolutionary radiation of pikas at the center of the origin of lagomorphs in East Asia and their subsequent geographic dispersal.

Is the propensity to emit alarm calls associated with health status?

The production and structure of animal signals may depend on an individual’s health status and may provide more than one type of information to receivers. While alarm calls are not typically viewed as health condition dependent, recent studies have suggested that their structure, and possibly their propensity to be emitted, depends on an individual’s health condition and state. We asked whether the propensity of yellow-bellied marmots (Marmota flaviventer) to emit calls is influenced by their immunological or parasite status, by quantifying both trap-elicited and natural calling rates as a function of their neutrophil-to-lymphocyte (NL) ratio, the presence of a blood borne trypanosome, and the presence of several intestinal parasites (Eimeria sp., Entamoeba sp., and Ascaris sp.). We fitted mixed effects models to determine if the health measures we collected were associated with the probability of calling in a trap and with annual rates of natural alarm calling. Marmots infected with a blood-borne trypanosome were marginally more likely to call naturally and when trapped, while those infected with the intestinal parasite Ascaris were less likely to call when trapped. NL ratio was not directly associated with in-trap calling probability, but males were more likely to call when they had higher NL ratios. Thus, health conditions, such as parasite infection and immune system activation, can modulate the production of alarm signals and potentially provide information to both predators and prey about the caller’s condition. Playback experiments are required to confirm if receivers use such information.

Social learning of acoustic anti-predator cues occurs between wild bird species

In many species, individuals gather information about their environment both through direct experience and through information obtained from others. Social learning, or the acquisition of information from others, can occur both within and between species and may facilitate the rapid spread of antipredator behaviour. Within birds, acoustic signals are frequently used to alert others to the presence of predators, and individuals can quickly learn to associate novel acoustic cues with predation risk. However, few studies have addressed whether such learning occurs only though direct experience or whether it has a social component, nor whether such learning can occur between species. We investigate these questions in two sympatric species of Parids: blue tits (Cyanistes caeruleus) and great tits (Parus major). Using playbacks of unfamiliar bird vocalizations paired with a predator model in a controlled aviary setting, we find that blue tits can learn to associate a novel sound with predation risk via direct experience, and that antipredator response to the sound can be socially transmitted to heterospecific observers, despite lack of first-hand experience. Our results suggest that social learning of acoustic cues can occur between species. Such interspecific social information transmission may help to mediate the formation of mixed-species aggregations.

Calling rhythm as a predictor of the outcome of vocal interactions: flight departure in pale-winged starling pairs

Vocal communication plays an important role in the regulation of social interactions and the coordination of activities in many animal species. Synchrony is an essential part of the establishment and maintenance of pair bonds, but few reports have investigated decision-making at the pair level. We investigated temporal characteristics of call exchanges in pale-winged starlings (Onychognathus nabouroup) that could predict whether one, two, or neither members of a pair would take off. Our analysis of these interactions revealed that the overall rhythm of a call exchange, as well as the acceleration towards the end of an interaction, were significantly associated with the type of behavioural outcome. Faster rhythms were associated with higher probabilities that both birds would fly away. Our results confirm the findings of previous studies showing that higher rates of alarm calls indicate imminent departure and highlight the relationship between temporal features of vocal interactions and their outcome.

Damsels in Distress: Oil Exposure Modifies Behavior and Olfaction in Bicolor Damselfish (Stegastes partitus)

In fishes, olfactory cues evoke behavioral responses that are crucial to survival; however, the receptors, olfactory sensory neurons, are directly exposed to the environment and are susceptible to damage from aquatic contaminants. In 2010, 4.9 million barrels of crude oil were released into the northern Gulf of Mexico from the Deepwater Horizon disaster, exposing marine organisms to this environmental contaminant. We examined the ability of bicolor damselfish (Stegastes partitus), exposed to the water accommodated fraction (WAF) of crude oil, to respond to chemical alarm cue (CAC) using a two-channel flume. Control bicolor damselfish avoided CAC in the flume choice test, whereas WAF-exposed conspecifics did not. This lack of avoidance persisted following 8 days of control water conditions. We then examined the physiological response to CAC, brine shrimp rinse, bile salt, and amino acid cues using the electro-olfactogram (EOG) technique and found that WAF-exposed bicolor damselfish were less likely to detect CAC as an olfactory cue but showed no difference in EOG amplitude or duration compared to controls. These data indicate that a sublethal WAF exposure directly modifies detection and avoidance of CAC beyond the exposure period and may suggest reduced predator avoidance behavior in oil-exposed fish in the wild.

Vocal contagion of emotions in non-human animals

Communicating emotions to conspecifics (emotion expression) allows the regulation of social interactions (e.g. approach and avoidance). Moreover, when emotions are transmitted from one individual to the next, leading to state matching (emotional contagion), information transfer and coordination between group members are facilitated. Despite the high potential for vocalizations to influence the affective state of surrounding individuals, vocal contagion of emotions has been largely unexplored in non-human animals. In this paper, I review the evidence for discrimination of vocal expression of emotions, which is a necessary step for emotional contagion to occur. I then describe possible proximate mechanisms underlying vocal contagion of emotions, propose criteria to assess this phenomenon and review the existing evidence. The literature so far shows that non-human animals are able to discriminate and be affected by conspecific and also potentially heterospecific (e.g. human) vocal expression of emotions. Since humans heavily rely on vocalizations to communicate (speech), I suggest that studying vocal contagion of emotions in non-human animals can lead to a better understanding of the evolution of emotional contagion and empathy.

Experience of the signaller explains the use of social versus personal information in the context of sentinel behaviour in meerkats

To maximise foraging opportunities while simultaneously avoiding predation, group-living animals can obtain personal information on food availability and predation risk and/or rely on social information provided by group members. Although mainly associated with low costs of information acquisition, social information has the potential to be irrelevant or inaccurate. In this study we use playbacks of individually distinct sentinel calming calls produced during sentinel behaviour, a form of coordinated vigilance behaviour, to show that meerkats (Suricata suricatta) discriminate between social information provided by different sentinels and adjust their personal vigilance behaviour according to the individual that is played back. We found that foraging group members acquired the lowest amounts of personal information when hearing social information provided by experienced individuals that act as sentinels most often in their group and littermates. Our study shows that social information can be flexibly used in the context of sentinel behaviour in order to optimize the trade-off between foraging and vigilance behaviours dependent on discrimination among signallers. We also provide novel evidence that the experience of sentinels rather than their age or dominance status is the main factor affecting the extent to which individuals use social information.

Social communication in bats

Bats represent one of the most diverse mammalian orders, not only in terms of species numbers, but also in their ecology and life histories. Many species are known to use ephemeral and/or unpredictable resources that require substantial investment to find and defend, and also engage in social interactions, thus requiring significant levels of social coordination. To accomplish these tasks, bats must be able to communicate; there is now substantial evidence that demonstrates the complexity of bat communication and the varied ways in which bats solve some of the problems associated with their unique life histories. However, while the study of communication in bats is rapidly growing, it still lags behind other taxa. Here we provide a comprehensive overview of communication in bats, from the reasons why they communicate to the diversity and application of different signal modalities. The most widespread form of communication is the transmission of a signaller's characteristics, such as species identity, sex, individual identity, group membership, social status and body condition, and because many species of bats can rely little on vision due to their nocturnal lifestyles, it is assumed that sound and olfaction are particularly important signalling modes. For example, research suggests that secretions from specialized glands, often in combination with urine and saliva, are responsible for species recognition in several species. These olfactory signals may also convey information about sex and colony membership. Olfaction may be used in combination with sound, particularly in species that emit constant frequency (CF) echolocation calls, to recognize conspecifics from heterospecifics, yet their simple structure and high frequency do not allow much information of individual identity to be conveyed over long distances. By contrast, social calls may encode a larger number of cues of individual identity, and their lower frequencies increase their range of detection. Social calls are also known to deter predators, repel competitors from foraging patches, attract group mates to roost sites, coordinate foraging activities, and are used during courtship. In addition to sound, visual displays such as wing flapping or hovering may be used during courtship, and swarming around roost sites may serve as a visual cue of roost location. However, visual communication in bats still remains a poorly studied signal modality. Finally, the most common form of tactile communication known in bats is social grooming, which may be used to signal reproductive condition, but also to facilitate and strengthen cooperative interactions. Overall, this review demonstrates the rapid advances made in the study of bat social communication during recent years, and also identifies topics that require further study, particularly those that may allow us to understand adaptation to rapidly changing environmental conditions.

Combined effects of physiological condition and environmental attributes in determining call plasticity

Evidence is growing on the ability of anurans to make immediate call adjustments in response to the propagation properties of the environment. However, our understanding of such flexibility is typically based on dichotomous stimuli (i.e. presence/absence), while its condition-dependence has been little explored. We experimentally studied the ability of adjustment and its condition dependence of advertisement calls of Hypsiboas pulchellus in response to different levels of attenuation. Individuals modified most call parameters analyzed, although the direction of adjustments was contingent on individual identity, level of attenuation and trait category (i.e. spectral or temporal). Under low attenuation conditions males lengthened some call elements, partially supporting the hypothesis of plasticity oriented towards maintaining signal transmission, but this trend was not present in the high attenuation treatment. Also, under both attenuation treatments males gave higher frequency notes, as expected from an energy-saving response to changes in social environment or reducing attractiveness due to risk perception. Across treatments individuals in better condition tended to exhibit higher plasticity. These results indicate that call structure could depend on the integration of different cues such as habitat propagation characteristics, acoustic competition for females, and predation risk, while the ability to behave flexibly depends on current body reserves.

Female vervet monkeys fine-tune decisions on tolerance versus conflict in a communication network

Group living promotes opportunities for both cooperation and competition. Selection on the ability to cope with such opposing social opportunities has been proposed as a driving force in the evolution of large brains in primates and other social species. However, we still know little about the degree of complexity involved in such social strategies. Here, we report advanced social strategies in wild vervet monkeys. Building on recent experimental evidence that subordinate females trade grooming for tolerance from higher-ranking individuals during foraging activities, we show that the audience composition strongly affects this trade. First, tolerance was lower if the audience contained individuals that outranked the subordinate partner, independently of audience size and kinship relationships. Second, we found a significant interaction between previous grooming and relative rank of bystanders: dominant subjects valued recent grooming by subordinates while intermediate ranked subjects valued the option to aggress subordinate partners in the presence of a dominant audience. Aggressors were also more likely to emit coalition recruitment calls if the audience contained individuals that outranked the subordinate partner. In conclusion, vervet monkeys include both recent grooming and knowledge about third-party relationships to make complex decisions when trading grooming for tolerance, leading to a finely balanced trade-off between reciprocation and opportunities to reinforce rank relationships.

Arousal dynamics drive vocal production in marmoset monkeys

Vocal production is the result of interacting cognitive and autonomic processes. Despite claims that changes in one interoceptive state (arousal) govern primate vocalizations, we know very little about how it influences their likelihood and timing. In this study we investigated the role of arousal during naturally occurring vocal production in marmoset monkeys. Throughout each session, naturally occurring contact calls are produced more quickly, and with greater probability, during higher levels of arousal, as measured by heart rate. On average, we observed a steady increase in heart rate 23 s before the production of a call. Following call production, there is a sharp and steep cardiac deceleration lasting ∼8 s. The dynamics of cardiac fluctuations around a vocalization cannot be completely predicted by the animal's respiration or movement. Moreover, the timing of vocal production was tightly correlated to the phase of a 0.1-Hz autonomic nervous system rhythm known as the Mayer wave. Finally, a compilation of the state space of arousal dynamics during vocalization illustrated that perturbations to the resting state space increase the likelihood of a call occurring. Together, these data suggest that arousal dynamics are critical for spontaneous primate vocal production, not only as a robust predictor of the likelihood of vocal onset but also as scaffolding on which behavior can unfold.

Dominance status predicts social fear transmission in laboratory rats

Acquiring information about stimuli that predict danger, through either direct experience or inference from a social context, is crucial for individuals’ ability to generate appropriate behaviors in response to threats. Utilizing a modified demonstrator–observer paradigm (fear conditioning by proxy) that allows for free interaction between subjects, we show that social dominance hierarchy, and the interactive social behaviors of caged rats, is predictive of social fear transmission, with subordinate rats displaying increased fear responses after interacting with a fear-conditioned dominant rat during fear retrieval. Fear conditioning by proxy conserves some of the pathways necessary for direct fear learning (e.g., lateral amygdala) but is unique in that it requires regions necessary for emotional regulation (e.g., anterior cingulate cortex), making this paradigm an important tool for evaluating learning and behavior in the laboratory setting.

The bark, the howl and the bark-howl: Identity cues in dingoes' multicomponent calls

Dingoes (genus Canis) produce a stereotyped bark-howl vocalisation, which is a unimodal complex signal formed by the concatenation of two call types (a bark and a howl). Bark-howls may function as alarm signals, although there has been no empirical investigation of this vocalisation's structure or function. We quantified the content and efficacy of the bark and howl segments separately and when combined, using 140 calls from 10 individuals. We found that both segments are individually distinctive, although howl segments are more accurately classified, suggesting a higher level of individuality. Furthermore, howls convey signature characteristics that are conserved across different contexts of production, and thus may act as 'identity signals'. The individual distinctiveness of full bark-howls increases above that of isolated segments, which may be a result of selection on improved signal discriminability. Propagation tests revealed that bark-howls are best described as medium-range signals, with both segments potentially allowing for individual discrimination up to 200m regardless of environmental conditions. We discuss our findings regarding the fitness benefits of encoding identity cues in a potential alarm call and propose additional hypotheses for the function(s) of bark and howl segments.

The acoustic structure of male giant panda bleats varies according to intersexual context

Although the acoustic structure of mammal vocal signals often varies according to the social context of emission, relatively few mammal studies have examined acoustic variation during intersexual advertisement. In the current study male giant panda bleats were recorded during the breeding season in three behavioural contexts: vocalising alone, during vocal interactions with females outside of peak oestrus, and during vocal interactions with peak-oestrous females. Male bleats produced during vocal interactions with peak-oestrous females were longer in duration and had higher mean fundamental frequency than those produced when males were either involved in a vocal interaction with a female outside of peak oestrus or vocalising alone. In addition, males produced bleats with higher rates of fundamental frequency modulation when they were vocalising alone than when they were interacting with females. These results show that acoustic features of male giant panda bleats have the potential to signal the caller's motivational state, and suggest that males increase the rate of fundamental frequency modulation in bleats when they are alone to maximally broadcast their quality and promote close-range contact with receptive females during the breeding season.