Production and perception of situationally variable alarm calls in wild tufted capuchin monkeys (Cebus apella nigritus)

Many mammalian and avian species produce conspicuous vocalizations upon encountering a predator, but vary their calling based on risk urgency and/or predator type. Calls falling into the latter category are termed “functionally referential” if they also elicit predator-appropriate reactions in listeners. Functionally referential alarm calling has been well documented in a number of Old World monkeys and lemurs, but evidence among Neotropical primates is limited. This study investigates the alarm call system of tufted capuchin monkeys (Cebus apella nigritus) by examining responses to predator and snake decoys encountered at various distances (reflecting differences in risk urgency). Observations in natural situations were conducted to determine if predator-associated calls were given in additional contexts. Results indicate the use of three call types. “Barks” are elicited exclusively by aerial threats, but the call most commonly given to terrestrial threats (the “hiccup”) is given in nonpredatory contexts. The rate in which this latter call is produced reflects risk urgency. Playbacks of these two call types indicate that each elicits appropriate antipredator behaviors. The third call type, the “peep,” seems to be specific to terrestrial threats, but it is unknown if the call elicits predator-specific responses. “Barks” are thus functionally referential aerial predator calls, while “hiccups” are better seen as generalized disturbance calls which reflect risk urgency. Further evidence is needed to draw conclusions regarding the “peep.” These results add to the evidence that functionally referential aerial predator alarm calls are ubiquitous in primates, but that noncatarrhine primates use generalized disturbance calls in response to terrestrial threats.     

Behavioural responses of Diana monkeys to male long-distance calls: changes in ranging,association patterns and activity

Although much is known about the relationship between vigilance, group size and predation risk, behavioural responses to predation risk and their resultant costs are less clear. We investigated the response of Diana monkeys to increased predation risk by looking at behavioural changes associated with male long-distance calls, which are reliably given to certain predators. After male long-distance calls, group spread and nearest-neighbour distance decreased whilst travel and association rates for the group increased. The average height and exposure level of individuals in the group did not change after calls. Individual Diana monkeys changed their behaviour and were more likely to be vigilant or travel and less likely to engage in social or resting behaviours after long-distance calls. In addition, movement rates increased with the number of species the Diana monkeys were associated with. Diana monkey long-distance calls facilitate the joining of groups of other species. Black and white colobus and lesser spot-nosed monkeys were more likely to be in an association following a long-distance call than before. Behavioural responses, such as increased travel or association rates, that reduce foraging efficiency are interpreted as evidence of a non-lethal impact of increased predation risk.     

A forest monkey’s alarm call series to predator models

Some non-human primates produce acoustically distinct alarm calls to different predators, such as eagles or leopards. Recipients respond to these calls as if they have seen the actual predator, which has led to the notion of functionally referential alarm calls. However, in a previous study with free-ranging putty-nosed monkeys (Cercopithecus nictitans martini), we demonstrated that callers produced two acoustically distinct alarm calls to eagle shrieks and leopard growls, but both alarm calls were given to both predators. We can think of two basic explanations for this surprising result, a methodological and theoretical one. Firstly, acoustic predator models may not always be suitable to test alarm call behaviour in primates, sometimes causing uncharacteristic behaviour. Secondly, referential alarm calling may not be a universal feature of primate alarm call systems. Considering the methodological and theoretical importance of these possibilities, we conducted a follow-up study using life-sized leopard, eagle, and human models on the same population and compared the resulting vocal responses to those given to acoustic predator models. We compared the alarm call series given to each of these predator model types and found a considerable degree of consistency suggesting that the mode of presentation did not affect anti-predator calling strategies. However, evidence for audience effects on calling behaviour was inconclusive. While it appears that predator class is reliably encoded by different call series types irrespective of the mode of presentation, observations of these same call series given in non-predatory contexts indicate that predator class is unlikely to be the relevant organising principle underlying the alarm-calling behaviour in this species. We conclude by offering an alternative, non-referential, account of the alarm-calling system exhibited by this species. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Individual specific contact calls of pallid bats (<Emphasis Type="Italic">Antrozous pallidus</Emphasis>) attract conspecifics at roosting sites

Contact calls are utilized by several bird and mammal species to maintain group cohesion and coordinate group movement. From a signal design perspective, contact calls typically exhibit acoustic features that make them easily localizable and encode information about individual or group identity. Pallid bats (Antrozous pallidus) are unusual among vespertilionids in that they often emit a loud, partially audible frequency-modulated social call several times in rapid succession while in flight. This call appears to function as a contact call in that it is frequently given when bats return from foraging and perform circular flights before entering a crevice roost. However, the degree to which pallid bats respond to the calls of conspecifics and what information is provided in the call is unknown. Thus, the goal of this study was to investigate pallid bat calling behavior to determine if calls attract roostmates or elicit responses from them and provide sufficient information for individual recognition. In playback studies, we found that contact calls, elicit calls, and approaches and that free-flying bats respond more to familiar than unfamiliar calls. In addition, analysis of frequency and temporal measurements of calls collected from multiple sites and spectral cross correlation analysis of calls recorded from the same radio-tagged bats on multiple evenings revealed that the frequency pattern of contact calls is highly repeatable over time within individuals but exhibits significant differences among individuals. Thus, contact call structure appears to be unique to individuals and stable through time, which makes these calls well-suited for roostmate recognition.     

Predation affects alarm call usage in female Diana monkeys (Cercopithecus diana diana)

Diana monkeys produce acoustically distinct calls to a number of external events, including different types of predators. In a previous study, we found population-wide differences in male alarm call production in Taï Forest, Ivory Coast, and on Tiwai Island, Sierra Leone, mostly likely originating from differences in predator experience. In Taï Forest, leopards (Panthera pardus) are common but on Tiwai Island they have been absent for decades, while the predation pressure from crowned eagles (Stephanoaetus coronatus) has been similar. To further evaluate the impact of predator experience, we here analyse the vocal behaviour of female Diana monkeys in both habitats. Female Diana monkeys produce predator-specific alarm calls, alert calls and contact calls in response to predators, suggesting that their calls serve in a broader range of functions compared to males. Results showed that females produced the same call types at both sites, despite the differences in predator fauna. Regarding call usage, leopard alarm calls were extremely rare on Tiwai Island, but not in Taï Forest, whereas we found no differences in eagle alarm call production. When comparing response latencies, Tiwai females were slower to respond to both predators compared to Taï females. Finally, we found no habitat-specific acoustic differences in the alert and predator-specific alarm calls, but significant differences in frequency-based parameters of contact calls. Overall, our results suggest that ontogenetic experience can affect primate vocal behaviour in both usage and acoustic structure but that the way in which particular call types are affected may be closely linked to function.     

Predator-specific alarm calls in Campbell's monkeys, Cercopithecus campbelli

One of the most prominent behavioural features of many forest primates are the loud calls given by the adult males. Early observational studies repeatedly postulated that these calls function in intragroup spacing or intergroup avoidance. More recent field experiments with Diana monkeys (Cercopithecus diana) of Taï Forest, Ivory Coast, have clearly shown that loud male calls function as predator alarm calls because calls reliably (1) label different predator classes and (2) convey semantic information about the predator type present. Here, I test the alarm call hypothesis another primate, the Campbell's monkey (C. campbelli). Like Diana monkeys, male Campbell's monkeys produce conspicuous loud calls to crowned hawk eagles (Stephanoaetus coronatus) and leopards (Panthera pardus), two of their main predators. Playback experiments showed that monkeys responded to the predator category represented by the different playback stimuli, regardless of whether they consisted of (1) vocalisations of the actual predators (crowned hawk eagle shrieks or leopard growls), (2) alarm calls to crowned hawk eagles or leopards given by other male Campbell's monkeys or (3) alarm calls to crowned hawk eagles or leopards given by sympatric male Diana monkeys. These experiments provide further evidence that non-human primates have evolved the cognitive capacity to produce and respond to referential labels for external events.     

Anti-predator behavior of group-living Malagasy primates: mixed evidence for a referential alarm call system

Many mammals warn conspecifics with alarm calls about detected predators. These alarm calls are either functionally referential, urgency based, or they can have multiple functions, including predator deterrence. The taxonomic distribution of these alarm call systems is uneven, with primates providing the best-known examples for a functionally referential system and rodents most examples of an urgency-based system. Reports of different alarm call systems in lemurid primates prompted us to examine the anti-predator behavior of two additional lemur species. In an experimental field study we exposed adult redfronted lemurs (Eulemur fulvus rufus) and white sifakas (Propithecus verreauxi verreauxi) to playbacks of vocalizations of their main aerial and terrestrial predators, as well as to their own alarm calls given in response to the presentation of these predators. We scored the subjects' immediate behavioral responses, including alarm calls, from video recordings made during the first minute following a playback. We found that both species gave specific alarm calls only in response to raptor playbacks and the corresponding alarm calls, whereas calls given in response to carnivores and the corresponding alarm calls were also observed in other situations characterized by high arousal. Other behavioral responses, such as gaze and escape directions, corresponded to the hunting strategies of the two predator classes, suggesting that the corresponding vocalizations were categorized correctly. These two lemur species, which represent different families, have therefore independently evolved a mixed alarm call system, characterized by functionally referential calls for diurnal raptors, but not for carnivores. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00265-001-0436-0 Electronic Publication     

Chick-a-dee call variation in the context of “flying” avian predator stimuli: a field study of Carolina chickadees (<Emphasis Type="Italic">Poecile carolinensis</Emphasis>)

Chick-a-dee calls function in social organization in Poecile (chickadee) species. Recent field and aviary studies have found that variation in chick-a-dee calls relates to the type or proximity of avian predator, or level of threat. Earlier studies on calls in the context of predator stimuli have typically used stationary and perched predator models. For chickadees and other small songbirds, more frequently detected and more dangerous avian predatory stimuli are flying predators. In the present study, we tested whether simulated flying avian predator and control models influenced chick-a-dee calling behavior of wild Carolina chickadees, Poecile carolinensis. At 20 independent field sites, chickadee subjects were presented with wooden models that were painted to resemble either a predatory sharp-shinned hawk (Accipiter striatus) or a blue jay (Cyanocitta cristata) and that were made to “fly” down a zip line near a feeding station chickadees were using. The note composition of chick-a-dee calls was affected by both the flight of stimuli and type of model. Call variation in this flying predator context suggests interesting similarities and differences with experimental findings with congeners. Finally, increased production of certain notes to the flying of both model types provides support for a “Better Safe than Sorry” strategy. When costs of alarm calling are low but costs of discriminating potentially serious threats may be extremely high, individuals should err on the side of caution, and alarm call to any potentially threatening stimulus.     

Predator guild does not influence orangutan alarm call rates and combinations

Monkey alarm calls have shown that in the primate clade, combinatorial rules in acoustic communication are not exclusive to humans. A recent hypothesis suggests that the number of different call combinations in monkeys increases with increased number of predator species. However, the existence of combinatorial rules in great ape alarm calls remains largely unstudied, despite its obvious relevance to ideas about the evolution of human speech. In this paper, we examine the potential use of combinatorial rules in the alarm calls of the only Asian great ape: the orangutan. Alarm calls in orangutans are composed of syllables (with either one or two distinct elements), which in turn are organized into sequences. Tigers and clouded leopards are predators for Sumatran orangutans, but in Borneo, tigers are extinct. Thus, orangutans make a suitable great ape model to assess alarm call composition in relation to the size of the predator guild. We exposed orangutans on both islands to a tiger and control model. Response compositionality was analyzed at two levels (i.e., syllable and syllable sequences) between models and populations. Results were corroborated using information theory algorithms. We made specific, directed predictions for the variation expected if orangutans used combinatorial rules. None of these predictions were met, indicating that monkey alarm call combinatorial rules do not have direct homologues in orangutans. If these results are replicated in other great apes, this indicates that predation did not drive selection towards ever more combinatorial rules in the human lineage.     

Chick-a-dee call syntax,social context,and season affect vocal responses of Carolina chickadees (<Emphasis Type="Italic">Poecile carolinensis</Emphasis>)

Chick-a-dee calls in many chickadee (Poecile) species are common vocal signals used in a diversity of social contacts. The calls consist of four notes, A, B, C, and D, which follow simple rules of syntax (note ordering and composition) to generate many unique call types. We used field playbacks with Carolina chickadees, P. carolinensis, to ask whether violations of a syntactical rule affected their vocal responses. We show that chickadee responses to typical calls (e.g. AAAACCCC and CCCCDDDD) differ from responses to atypical calls (e.g. CACACACA and DCDCDCDC) depending on playback note composition, season, and social context (presence of heterospecifics). In the fall/winter, playbacks of typical calls with A and C notes elicited the greatest number of A and B notes in chick-a-dee call responses and typical calls with D notes elicited the greatest number of C notes, when in the presence of heterospecifics. In contrast, the corresponding atypical calls did not elicit similar responses. This suggests communicative significance is lost in calls that violate a rule of syntax in the fall/winter. In the spring, neither chickadee feebeefeebay song rate nor chick-a-dee calls responses differed by playback type. We suggest that call syntax is less salient for mated pairs in the spring than it is for fall/winter flocks that rely more on conspecific communication for foraging success and flock cohesion. This study represents the first experimental evidence that chickadees attend to both note composition and ordering in chick-a-dee calls.Communicated by W.A. Searcy     

The effect of pup vocalisations on food allocation in a cooperative mammal, the meerkat (Suricata suricatta)

In the meerkat (Suricata suricatta), a cooperative mongoose, pups follow potential feeders while the group is foraging and emit incessant calls when soliciting food from them. In contrast to a ’stationary’ brood of chicks, in which nestlings are fed at a fixed location, meerkat pups are ’mobile’ and become spread out. The question arises whether meerkat pups that experience different constraints to those facing chicks have evolved similar begging strategies. This paper describes the vocalisations that meerkat pups emit in the context of begging and investigates the influence of these calls on food allocation by older group members and on the behaviour of littermates. Meerkat pups use two types of calls when soliciting food from a potential feeder. The most common is a ’repeat’ call, which pups emit continuously when following an older forager over several hours a day. In addition, when a potential feeder finds a prey item, the pups next to it emit a bout of calls with increased calling rate, amplitude and fundamental frequency, termed ’high-pitched’ calls. Observations, together with playback experiments, showed that more prey was allocated to pups that called longer and more intensely. The pup closest to a feeder was almost always fed. The probability of emitting high-pitched calls did not depend on the time since a pup had received food, and the change from repeat to high-pitched calls occurred suddenly. The main function of the high-pitched call, therefore, does not appear to be to signal a pup’s hunger state. More likely, the two calls, in the context of begging, may be an adaptation to energetic constraints in a mobile feeding system. Pups, which are dispersed during foraging, may emit repeat calls over long periods to prevent potential feeders from eating all the prey themselves. At the moment a potential feeder finds prey, pups may give the more intense high-pitched calls to direct feeders to bring the food item to them and not to a littermate. Therefore, unlike the stationary feeding system where chicks emit one type of begging call when the feeder approaches the nest, meerkats, with a mobile feeding system, have evolved two discrete types of vocalisations in the context of begging. Received: 22 November 1999 / Revised: 1 July 2000 / Accepted: 17 July 2000     

Species-specificity and individual variation in the song of male Nathusius’ pipistrelles (<Emphasis Type="Italic">Pipistrellus nathusii</Emphasis>)

Sequences of the advertisement calls produced by male Nathusius’ pipistrelles (Pipistrellus nathusii) during the autumn mating period were recorded from individuals at two separate sites in Antrim, Northern Ireland, in August 2004. Several male roosts were found at these sites in close proximity to a single maternity roost, each containing approximately 200 adult females and their young. Analysis of measured parameters of four identified call types revealed that there were significant differences in call structure between sites and between individuals. Playback experiments, performed outside the adult female and juvenile roost sites, comprised of experimental advertisement call sequences of P. nathusii, Pipistrellus pygmaeus and Pipistrellus pipistrellus and control sound recorded without bats present (silence). Response was measured by simultaneously recording ultrasound during playbacks and counting the number of echolocation pulses identified as those of P. nathusii above a predetermined amplitude threshold. Significantly greater numbers of P. nathusii echolocation pulses were recorded during playback of male P. nathusii advertisement calls than during playback of congeners’ advertisement calls and control sound. The number of echolocation pulses recorded was similar during playback of P. pipistrellus and P. pygmaeus advertisement calls and silence. We suggest that, due to call complexity, male P. nathusii advertisement calls should be classified as ‘song’. Species-specificity and individual variation suggests that the songs of male P. nathusii have the potential to play a role in mate attraction and mate assessment.     

Alarm calls of Belding's ground squirrels to aerial predators: nepotism or self-preservation?

Summary Belding's ground squirrels (Spermophilus beldingi) give acoustically distinct alarm calls to aerial and terrestrial predators. The animals typically give multiple-note trills to predatory mammals, and single-note whistles to flying hawks. During a 9-year study of free-living S. beldingi at Tioga Pass, California, the adaptive significance of the whistle call was investigated. Data were gathered on 664 ground squirrel-hawk interactions, most of which were induced by flying trained raptors over individually marked study animals of known sex and age. The sight of a flying hawk and the sound of whistles stimulated widespread calling and running to shelter by the ground squirrels (Fig. 1). Wild raptors were rarely successful at capturing the rodents once a whistle had been given, and fewer callers than noncallers were killed (Table 1). Individuals of both sexes and all ages whistled equally often (Fig. 4), and females' tendencies to whistle were not affected by the presence of relatives, including offspring (Fig. 5). The most frequent callers were animals in exposed positions: far from cover and close to the predatory bird (Table 2). Taken together the data suggest that unlike trills, which increase vulnerability to terrestrial predators (Table 1) and function to warn relatives, whistle directly benefit callers by increasing their chances of escaping from hawks.     

Postcopulatory mate guarding by vocalization in the Formosan squirrel

The Formosan squirrel, Callosciurus erythraeus thaiwanensis, emitted different vocalizations in response to terrestrial and aerial predators and snakes. Each vocalization caused nearby individuals to adopt a different type of anti-predator behaviour. In mating bouts, males produced two types of loud calls: precopulatory calls, emitted before copulations, and postcopulatory calls, emitted after copulations. The latter continued for 17 min on average. The estrous female and other males attending the mating bouts stopped moving during the postcopulatory call, so that the calling male was able to tend the female without interruption. The sound characteristics of anti-terrestrial-predator and postcopulatory calls recorded in the captivity were compared, and none of the ten characters of duration and frequency measured differed between the two calls. Playback experiments also showed that responses to the sounds in two different contexts, escape behaviour and defensive immobility, did not differ. The similarity between anti-predator and postcopulatory calls is discussed with reference to the possibility of manipulation and other explanatory hypotheses.     

Do yellow-bellied marmots respond to predator vocalizations?

We conducted four experiments to determine whether yellow-bellied marmots, Marmota flaviventris, discriminate among predator vocalizations, and if so, whether the recognition mechanism is learned or experience-independent. First, we broadcast to marmots the social sounds of coyotes, Canis latrans, wolves, Canis lupus, and golden eagles, Aquila chrysaetos, as well as conspecific alarm calls. Coyotes and eagles are extant predators at our study site, while wolves have been absent since the mid-1930s. In three follow-up experiments, we reversed the eagle call and presented marmots with forward and reverse calls to control for response to general properties of call structure rather than those specifically associated with eagles, we tested for novelty by comparing responses to familiar and unfamiliar birds, and we tested for the duration of predator sounds by comparing a wolf howl (that was much longer than the coyote in the first experiment) with a long coyote howl of equal duration to the original wolf. Marmots suppressed foraging and increased looking most after presentation of the conspecific alarm call and least after that of the coyote in the first experiment, with moderate responses to wolf and eagle calls. Marmots responded more to the forward eagle call than the reverse call, a finding consistent with a recognition template. Marmots did not differentiate vocalizations from the novel and familiar birds, suggesting that novelty itself did not explain our results. Furthermore, marmots did not differentiate between a wolf howl and a coyote howl of equal duration, suggesting that the duration of the vocalizations played a role in the marmots’ response. Our results show that marmots may respond to predators based solely on acoustic stimuli. The response to currently novel wolf calls suggests that they have an experience-independent ability to identify certain predators acoustically. Marmots’ response to predator vocalizations is not unexpected because 25 of 30 species in which acoustic predator discrimination has been studied have a demonstrated ability to respond selectively to cues from their predators.     

Female and male behavioral response to advertisement calls of graded complexity in túngara frogs, <Emphasis Type="Italic">Physalaemus pustulosus</Emphasis>

We investigated the natural dynamics in a sexual signal that combines different call components and explored the role of call complexity in sexual selection using a neotropical frog. Male túngara frogs, Physalaemus pustulosus, facultatively add up to seven short, multi-harmonic components (chucks) to the simple form of their calls (whines). Female túngara frogs are preferentially attracted to whines with chucks over whines without chucks, and males also call more in response to calls containing chucks. Because acoustic predators prefer complex calls, in the context of simple (no chucks) versus complex (any number of chucks) calls, the variably complex call appears to have evolved in response to the opposing selective forces of natural and sexual selection. There is no evidence, however, for the function of increasing the number of chucks within complex calls. We tested two aspects of increasing call complexity: natural patterns of use of call types in males and how both sexes respond to variation in multi-chuck calls. Males incrementally change call complexity by the addition or subtraction of a single chuck and usually do not produce more than two chucks. Variation in call complexity, for calls with at least one chuck, does not influence response calling in males or phonotaxis in females. Our results suggest that one reason for not increasing call complexity beyond a single chuck is the diminishing effectiveness on the responses of both sexes. This is a posthumous publication for A. Stanley Rand     

Responses of pikas (Ochotona princeps,Lagomorpha) to naturally occurring terrestrial predators

Summary The responses of individually marked pikas (Ochotona princeps) to terrestrial predators were investigated in 1980 and 1981 in the Rocky Mountains of Colorado. Pikas uttered short call vocalizations in a variety of contexts: preceding or following an individual's movement, and in response to conspecifics, other nonpredaceous mammals and predators. Adult pikas apparently discriminated contexts in which predators were present by short calling more frequently and for longer duration compared with calling in nonpredator contexts. Short calls uttered by juveniles were similar in all contexts.Adults responded differently to two types of terrestrial predators: weasels and pine martens. Pikas called less frequently in response to weasels than to martens and avoided weasels more often than martens. They delayed the initiation of calling following the first sighting of a weasel more often than to martens. Weasels were determined to be more effective predators of pikas than martens, and these asymmetries in behavior and alarm vocalizations may indicate that responses reduce an individual's risk of predaton by weasels.Both male and female pikas called in response to predators, and residents called more often than nonresidents. The possible function of predator-related vocalization in pikas is discussed. It is suggested that calls to predators may function to warn local residents, which in pikas are usually closely related.     

Bats aloft: variability in echolocation call structure at high altitudes

Bats alter their echolocation in response to changes in ecological and behavioral conditions, but little is known about how they adjust call structure in response to changes in altitude. We examined altitudinal variation in the echolocation of Brazilian free-tailed bats, Tadarida brasiliensis, a species known to fly to altitudes of 3,000 m above the ground. From 50.2 h of recordings, we analyzed 113 high-quality echolocation call sequences recorded from 0 to 862 m above ground level. Bats flying near the ground used shorter, higher-frequency, broader-bandwidth calls compared to bats at higher altitudes, an effect likely due to the greater levels of echo-producing clutter (i.e., vegetation, buildings) found near the ground. When ground-level recordings are excluded, bats continue to shift towards the use of longer-duration, lower-frequency, narrower-bandwidth calls with increasing altitude. We propose that the observed high-altitude changes in call structure are a response to changing acoustic attenuation rates and/or decreasing insect densities at higher altitudes.     

Information content of female copulation calls in wild long-tailed macaques (<Emphasis Type="Italic">Macaca fascicularis</Emphasis>)

Primates are unusual in that many females display sexual signals, such as sex skin swellings/colorations and copulation calls, without any sex role reversal. The adaptive function of these signals remains largely unclear, although it has been suggested that they provide males with information on female reproductive status. For sex skin swellings, there is increasing evidence that they represent a graded signal indicating the probability of ovulation. Data on the functional significance of copulation calls are much scarcer. To clarify the information content of such calls, we recorded copulation calls in wild long-tailed macaques (Macaca fascicularis) and analysed the structure of these calls during the ovarian cycle. Specifically, we correlated selected call parameters with the female oestrogen to progestogen ratio (obtained from faecal samples), which are known to be elevated during the female's fertile phase. In addition, we ran a general linear mixed model for these call parameters, testing factors (cycle phase, occurrence/absence of ejaculation, male dominance status, occurrence/absence of mate guarding) which potentially influence female copulation calls in primates. Our results show that copulation calls of female long-tailed macaques signal mating outcome and rank of the mating partner, but not female reproductive status. They also show for the first time on primates that copulation calls can convey information on whether a female is mate guarded or not. We suspect that the function of these calls is manipulation of male mating and mate-guarding behaviour and that in this way the degree of sperm competition and ultimately male reproductive success is influenced.