Sex Differences in the Song of <Emphasis Type="Italic">Indri indri</Emphasis>

In some primate species, males and females within a social group emit loud calls in a coordinated manner or chorus. Indri indri emits a very conspicuous loud call that elicits the loud calls of neighboring groups. Previous investigations have hypothesized that the main functions of the indri chorus are related to territorial announcement, intergroup avoidance, and group cohesion. We investigated sex differences in indri song. We recorded and analysed songs given by 10 different groups over 160 d. Overall singing duration did not vary between the sexes. However, males emitted significantly fewer but longer notes. Adult males and females of each group participated in the song with sex-specific repertoires. Females had a song repertoire of 8 note types; males shared all of their 6 notes with females. Apart from the initial roars, in all note types shared by both sexes, male notes were significantly longer than female ones, whereas variations in frequency parameters differed according to the note type. These findings suggest that indri song may provide cues to conspecifics, such as group size and sex composition, which could influence interactions between groups.     

Species differences of male loud calls and their perception in sulawesi macaques

Playback experiments were conducted to investigate interspecific discrimination of male loud calls in Sulawesi macaques. Loud calls of four macaque species living in Sulawesi (Macaca tonkeana, M. maurus, M. hecki, andM. nigrescens) and a control stimulus (an 8-sec frequency modulated sound) were played back to semi-free-ranging Tonkean macaques (M. tonkeana). A preliminary acoustic analysis indicated that the calls of these four species differ in some spectral and temporal features. In the playback experiments, Tonkean macaques responded in a similar manner to conspecific calls and calls of two other species,M. maurus andM. hecki. In contrast, animals responded more weakly to the call ofM. nigrescens and the control stimulus. Males responded more strongly than females to all stimuli, while females appeared to be more discriminating for species differences than males. Analyses on the acoustic features of loud calls suggested that high frequency, wide frequency range, and repetition of sound units at a high rate elicit quick responses from animals.     

Active choice, passive attraction and the cognitive machinery of acoustic preferences

Female preferences for loud calls are widespread among animals that communicate acoustically, but their ‘strategic’ role is still controversial. According to the ‘passive attraction’ hypothesis, females are more likely to respond to loud calls simply because these calls are more effective at stimulating their acoustic receptors and primary neurons. The ‘active choice’ hypothesis, however, assumes that females use sound intensity as a cue to assess the power and location of sound sources and to respond accordingly. To test which hypothesis could best explain the preference for loud calls of female green toads, Bufo viridis, we carried out multitrial discrimination experiments, in which females were given a choice between two stimuli differing in either the power or the distance of their sources or both. In the laboratory, females could discern differences in intensity caused by differences in power or location of the acoustic sources. This ability increased in field experiments, when the speakers and receivers were further apart than in the laboratory experiments. Phonotactic behaviour did not vary significantly between females, but did within females: in their second trial, females were more likely to approach the closer speaker than in the first trial. These findings suggest that sound intensity plays a more complex role in female mate choice than that recognized by the passive attraction hypothesis. To understand female preferences and, ultimately, mate choice, attention should be focused directly on the computational processes of the female's central nervous system.     

Acoustic Features of Female Chacma Baboon Barks

We studied variation in the loud barks of free-ranging female chacma baboons ( Papio cynocephalus ursinus ) with respect to context, predator type, and individuality over an 18-month period in the Moremi Game Reserve, Botswana. To examine acoustic differences in relation to these variables, we extracted a suite of acoustic parameters from digitized calls and applied discriminant function analyses. The barks constitute a graded continuum, ranging from a tonal, harmonically rich call into a call with a more noisy, harsh structure. Tonal barks are typically given when the signaler is at risk of losing contact with the group or when a mother and infant have become separated (contact barks). The harsher variants are given in response to large predators (alarm barks). However, there are also intermediate forms between the two subtypes which may occur in both situations. This finding is not due to an overlap of individuals' distinct distributions but can be replicated within individuals. Within the alarm bark category, there are significant differences between calls given in response to mammalian carnivores and those given in response to crocodiles. Again, there are intermediate variants. Both alarm call types are equally different from contact barks, indicating that the calls vary along different dimensions. Finally, there are consistent, significant differences among different individuals' calls. However, individual identity in one call type cannot directly be inferred from knowledge of the individuals' call characteristics in the other. In sum, the barks of female baboons potentially provide rich information to the recipients of these signals. The extent to which baboons discriminate between alarm and contact barks, and classify calls according to context and/or acoustic similarity will be described in a subsequent paper.     

The study of vocal communication of wild mandrills in Cameroon in relation to their social structure

The vocal repertoire of the mandrill (Mandrillus sphinx), a forest living baboon, is described, and their vocal communication analyzed quantitatively. Although the vocal repertoire of mandrills corresponds well to that of savanna living baboons,Papio, some characteristics differed, such as the development of long-distance calls and differentiation of vocalizations between age-sex classes. Vocal communication within a group was closely related to changes in the spatial distribution of group members, and the two most common vocalizations, crowing and 2PG, appear to function as contact calls. Based on the wide dispersion of food trees, a group of mandrills divided into several feeding groups (subgroups). The two types of contact call were given in different and in some senses complementary contexts, and helped to facilitate and maintain group integration. According to their acoustic structure, these calls are long distance calls. Influenced by the high-level of attenuation of vocalization on the forest floor, the mandrill has developed them as contact calls, instead of using the contact “grunt,” which is common to the savanna living baboons. Comparing the patterns of vocal exchanges of mandrills with those of gelada and hamadryas baboons which have a multi-levelled society, the social structure of the mandrill is discussed. From the analysis of the spatial distribution of vocal emission, a number of clusters of vocalizations were obtained. These clusters correspond to subgroups. The frequent female-female and female-male vocal exchange between subgroups of mandrills suggest that the relationships between subgroups are less closed than between the one-male units of gelada and hamadryas baboons. Furthermore some of these clusters include more than two vocalizing adult males, while in other clusters there are no vocalizing adult males. Thus, the social structure of mandrills is suggested to be multi-male rather than a multilevelled type. The absence of contact calls specific for short distance and the functional replacement of the grunting of all group members by persistent emission of a loud call (2PG) by usually just one adult male suggests that the social structure of mandrills is not exactly equivalent to that of the multimale troop of savanna living baboons. Usually the use of 2PG is monopolized by one adult male travelling in the rear part of the group. Such monopolization of 2PG emission and the pattern of 2PG-2PG or 2PG-roar exchanges by adult males in some cases indicate the existence of strong dominance relationships among adult males, and especially the existence of a leader male within a multi-male group of mandrills.     

Acoustic Properties of Long Calls Given by Flanged Male Orang‐Utans (Pongo pygmaeus wurmbii) Reflect Both Individual Identity and Context

Long calls by flanged male Bornean orang‐utans (Pongo pygmaeus wurmbii) serve as a long‐distance communication signal in this semi‐solitary species and allow individuals to adjust their ranging behavior. Long calls can be heard up to circa 1 km in dense rainforest. Only flanged males emit them, in various contexts: spontaneously (where no disturbances from the environment are perceived by human observers), when highly aroused by another male’s long call or a falling tree nearby, or right after having pushed over a dead tree themselves. In this study, acoustic analyses of orang‐utan long calls at Tuanan in Central Kalimantan not only confirm the discrimination of individual males by their long calls but also demonstrate the discrimination of context based on the long calls’ acoustic structure, which is further supported by the females’ ranging responses according to long call contexts. Females with dependent offspring move away from spontaneous long call sources but appear to ignore long calls elicited by disturbance. Hence, Bornean orang‐utan females perceive measurable differences in acoustic characteristics of long calls given in different contexts. These findings concur with vocal discrimination of contexts in other non‐human primates.     

Sex differences in leadership during group movement in mantled howler monkeys (Alouatta palliata)

Benefits of group life depend in large part on whether animals remain cohesive, which often requires collective decisions about where and when to move. During a group movement, the leader may be considered as the individual occupying the vanguard position of the group progression, when its movement evokes following by other group members. In nondespotic societies, individuals with greater incentives to move frequently are leaders. During 15 months of observations (1,712 contact hours), we investigated two mantled howler monkey (Alouatta palliata) groups at La Flor de Catemaco (Los Tuxtlas, Mexico) to examine whether sex and female reproductive state influenced leadership likelihood in two contexts: movements toward feeding trees; movements associated with loud calls, a group-defense behavior used by males of this genus. Females led and occupied forward positions during group movements toward feeding trees more often than adult males. Adult females led these movements more frequently when they were gestating than when they were lactating or cycling. There were no differences between sexes in the leadership of group movements associated with loud calls. Leadership by gestating females is perhaps the result of their higher nutritional/energetic needs when compared with cycling females, and of their greater mobility when compared with lactating females carrying dependent offspring. Female leadership during movements toward feeding trees may be a mechanism to optimize access to food resources in mantled howler monkeys.     

Individual and Contextual Variation in Thomas Langur Male Loud Calls

Individual and contextual differences in male loud calls of wild Thomas langurs (Presbytis thomasi) were studied in northern Sumatra, Indonesia. Loud calls were given in the following contexts: morning calls, vocal responses to other groups, between‐group encounter calls and alarm calls. Loud call spectrograms were analysed for a large number of variables. With discriminant analyses, 14 variables were found to be important in distinguishing individuals and contexts. Loud calls were assigned to the correct individual in 95.6% of the cases (91.8% with ‘leave‐one‐out’ validation) and to the correct context in 52.2% of the cases (39.0% with ‘leave‐one‐out’ validation). Further analyses with two‐way anova s showed significant differences in both temporal and frequency variables between individuals and contexts. Loud calls seemed to differ between the contexts in functionally meaningful ways, relating to the distance of the intended receivers and to the urgency of the message. Observation showed that females in the caller's group collected infants more often in the between‐group encounter context and in the alarm call context than in the vocal exchange context. These differential responses suggest that the monkeys also perceive the measurable differences in loud call characteristics between the various contexts.     

Loud calls of male Nilgiri langurs (Presbytis johnii): Age-, individual-, and population-specific differences

Adult male Nilgiri langurs (Presbytis johnii) utter loud call bouts consisting of one or more phrases. Phrases are made up of several units showing similar or different structural features. The units involved differ with respect to not only their physical structure but also their overall utilization: three vocal patterns are uttered exclusively by mature males living in bisexual groups or all-male bands and, in addition to being part of loud call bouts, are given during encounters with terrestrial predators; two vocal patterns are uttered by males and females, again not just as constituents of loud calls; and one vocal pattern is given exclusively by mature males living in bisexual groups. Within a given bout, phrases differ not only with respect to their composition but also in their temporal organization. In addition to the acoustic components, loud calls are regularly accompanied by stereotyped motoric displays. The motoric and acoustic components of loud call displays appear independently of each other and at different times during ontogeny. The development of the display is characterized by combination of units with different structural features and synchronization of vocal and motoric components. Although more evidence is needed, our observations suggest that the development of loud call displays coincides with the aquisitation of social maturation and competence and requires not only social experience but also a certain amount of motoric training. In spite of the high degree of ritualization, loud call displays are not completely fixed in form, but instead are open to individual- and population-specific variation.     

Copulation Calls in Female Chimpanzees (<Emphasis Type="Italic">Pan troglodytes schweinfurthii</Emphasis>) Convey Identity but Do Not Accurately Reflect Fertility

Copulation calls are a relatively common feature of female primate behavior thought to function in the advertisement of female receptivity and subsequent incitation of male–male competition. To date, the majority of work on copulation calling behavior has focused on various monkey species, with little empirical evidence from the great apes. Previous research on wild chimpanzees (Pan troglodytes schweinfurthii) has suggested that estrous females produce copulation calls to avoid monopolization by single males and to minimize competition from other females. We here extended these findings by investigating to what degree these social demands were reflected in the calls’ acoustic structure. We recorded and acoustically analyzed 71 copulation call bouts from 6 adult female chimpanzees in the Budongo Forest, Uganda. We did not find any acoustic differences in calls given by females in fertile and nonfertile periods, as assessed by their hormonal profiles. However, the calls’ acoustic structure did reliably encode identity cues of the calling female. We propose that, in chimpanzees, the use and morphology of copulation calls have jointly been shaped by the selective advantage of concealing fertility. Owing to the low visibility conditions associated with chimpanzees’ natural forest habitat and their dispersed social system, providing identity cues may be of particular biological relevance for these nonhuman primates.     

The function of three main call types in common cuckoo

Acoustic signals play a key role in shaping the relationships in birds. Common cuckoos Cuculus canorus are known to produce various call types, but the function of these calls has only been studied recently. Here, we used a combination of field recordings (conducted in 2017) and playback experiments (conducted in 2018) to investigate the functional significance of common cuckoo calls. We found significant differences in the characteristics between male two‐element “cu‐coo” and three‐element “cu‐cu‐coo” calls, with these two call types being used in different contexts. The three‐element male “cu‐cu‐coo” calls were associated with females emitting their “bubbling” call. Playback experiments revealed that both males and females exhibit stronger responses to playing female “bubbling” calls than with the calls of the Eurasian sparrowhawk (Accipter nisus) serving as a control, suggesting a significant intraspecific communication function for this call type. However, we did not find any evidence to support mate attraction in male calls, as females were not stimulated by playback of male calls compared with sparrowhawk calls in the control group.     

Acoustic and Temporal Variation in Gelada (<Emphasis Type="Italic">Theropithecus gelada</Emphasis>) Loud Calls Advertise Male Quality

Many animals rely on information from vocal signals to assess potential competitors and mates. For example, in primates, males use loud calls to assess rivals when the acoustic properties of the calls reliably indicate the condition or quality of the sender. Here, we investigate whether the loud calls of male geladas (Theropithecus gelada) function as a quality signal. Gelada males produce loud calls during ritualistic chases with rival males. Given the physically taxing nature of these displays, we hypothesize that variation in the acoustic properties of loud calls reliably signal male stamina or competitive ability. To test this hypothesis, we examined whether the acoustic properties of the gelada loud call varied in relation to individual, age, status, and exhaustion. Specifically, we examined 12 call parameters (e.g., fundamental frequency) and 3 bout parameters (e.g., number of calls per bout), that have been previously shown to vary across condition in male primates. We found that several acoustic features varied consistently across age and status such that males deemed higher quality in gelada society (e.g., high status) produced more calls per bout, produced calls that were lower in overall frequency measures, and exhibited a greater vocal range. In addition, we found that similar acoustic features varied with exhaustion; after a long chase event, males produced both fewer calls per bout and calls with higher spectral measures. Results from this study are consistent with the hypothesis that gelada loud calls are quality signals, contributing to the growing evidence that primates may use acoustic information to assess the quality of a rival or a potential mate.     

Effects of body size on selectivity for mating cues in different sensory modalities

We investigated the effects of body mass on the selectivity of female mating preferences in two different sensory channels (acoustic and chemical) using the field cricket, Gryllus integer. We found that body mass affected female selectivity for acoustic cues: larger females were more selective than smaller females for long‐distance calls of males. In contrast, body mass did not affect selectivity for chemical cues of males, which are assessed at close range. Nevertheless, we observed selectivity for these cues. Finally, selectivity for acoustic cues was not correlated with selectivity for chemical cues. These results suggest that energetic concerns may influence mating decisions made at a distance and that the effects of body mass on mating decisions are not necessarily shared across different sensory modalities. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 160–168.     

Sexual dimorphism and species differences in the neurophysiology and morphology of the acoustic communication system of two neotropical hylids

We examined auditory tuning and the morphology of the anatomical structures underlying acoustic communication in female Hyla microcephala and H. ebraccata and compared our findings to data from a previous study (Wilczynski et al. 1993) in which we showed species differences in the traits that in males relate to differences in the species-typical calls. Female species differences in the best excitatory frequency (BEF) of the basilar papilla (BP) were similar to the differences seen in males, and females had a significantly lower BEF in H. ebraccata, but not H. microcephala. In both species, females had lower BP thresholds. Snout-vent length, head width, and tympanic membrane diameters were sexually dimorphic in both species and larger in females, whereas laryngeal components were sexually dimorphic and larger in males. Middle and inner ear volumes were not sexually dimorphic. Despite the significant species differences in laryngeal morphology seen in males, female larynges are not significantly different. Furthermore, the interaction of species and sex differences resulted in significantly different degrees of sex dimorphism in the species, particularly for the larynx, which is more sexually dimorphic in H. microcephala, and measures of body size, which are more dimorphic in H. ebraccata. Accepted: 6 December 1996     

Responses to natural and synthetic phee calls by common marmosets (Callithrix jacchus)

Captive adult common marmosets (Callithrix jacchus) produce whistlelike “phee” calls in two contexts: in the home cage, where phee calls may function as part of territorial marking behavior, and when separated from social companions, where phee calls may function to reunite conspecifics. Natural and synthesized calls representing the acoustic structure of male and female calls in each context were presented to adult marmosets in a playback paradigm. Marmosets demonstrated discriminative abilities according to the context of the call and the caller's sex. Vocal and behavioral responses indicated increased vigilance and territorial behavior, following playbacks of naturally produced calls as well as synthetic calls. All animals scanned more frequently following produced calls as well as synthetic calls. All animals scanned more frequently following natural home cage as well as isolation calls, but only increased contact behavior (trills) in response to home cage calls. The responses were dimorphic according to the sex of the caller, where adult males scanned more following male calls, and adult females were more aggressive following male and female calls. The differential behavioral responses to playbacks of marmoset phee calls suggest a biological relevance to subtle differences found in the acoustic parameters of the phee call. © 1994 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, in the public domain in the United States of America.

     

The structure and usage of female and male mouse ultrasonic vocalizations reveal only minor differences

Ultrasonic vocalizations (USV) of mice are increasingly recognized as informative dependent variables in studies using mouse models of human diseases. While pup vocalizations primarily serve to re-establish contact with the mother, adult male "songs" were considered to be courtship signals. Alternatively, mouse USVs may generally function as territorial signals. To distinguish between these two hypotheses, we compared the structure and usage of adult male and female USVs in staged resident-intruder encounters. If calls function primarily as courtship signals, males should respond stronger than females, specifically when presented with a female intruder. Refuting this hypothesis, we found that in response to female intruders, females called more than males (228±32 calls/min vs. 71±15 calls/min), and males called more to female than to male intruders (14±7.5 calls/min). There were no significant differences in the acoustic characteristics of the calls given by females and males. To control for the influence of the intruder's behavior on calling, we repeated the experiments using anaesthetized intruders. Again, females produced more calls to female than male intruders (173±17 calls/min vs. 71±15 calls/min), while males called more in response to female than male intruders (39±17 calls/min), and there were no acoustic differences in female and male calls. The vocal activity did not differ significantly with regard to intruder state (awake or anaesthetized), while the acoustic structure exhibited significant differences. Taken together, our findings support the view that calls do not mainly function as courtship signals, although they might serve both a territorial (sex-independent) and a courtship function. The comparison of responses to awake vs. anaesthetized intruders suggests that the latter are sufficient to elicit vocal activity. The subtle acoustic differences, however, indicate that the subject differentiates between intruder states.     

Production of plumage ornaments among males and females of two closely related tropical passerine bird species

The evolution of elaborate secondary sexual traits (i.e., ornaments) is well‐studied in males but less so in females. Similarity in the appearance of ornaments between males and females supports the view that female ornaments arise as a neutral byproduct of selection on male traits due to genetic correlation between sexes, but recent research suggests an adaptive function of female ornaments in at least some contexts. Information on the degree to which production of ornaments differs between the sexes can shed light on these alternative perspectives. We therefore characterized the structural underpinnings of melanin‐based plumage production in males and females of two closely related passerine bird species (genus Malurus). Importantly, both ornamented and unornamented phenotypes in each sex are present between these two species, providing an opportunity to test the null expectation of equivalent modes of production in male and female ornamented phenotypes. In Malurus alboscapulatus, ornamented females are qualitatively similar to males, but we describe a distinctive ornamented female phenotype that differs from that of males in lacking a blue sheen and in lower feather barbule density. In M. melanocephalus, unornamented males and females are also similar in appearance, and we describe a similarity between unornamented phenotypes of males and females in both color and underlying feather barbule structure and pigment composition. Unornamented male M. melanocephalus can flexibly transition to the ornamented phenotype in weeks, and we found extreme differences in color and feather structure between these two alternative male phenotypes. These results contradict the idea that female ornaments have evolved in this system following a simple switch to male‐like plumage by demonstrating greater complexity in the production of the ornamented phenotype in males than in females.     

Life-Phase Related Changes in Male Loud Call Characteristics and Testosterone Levels in Wild Thomas Langurs

Males in many primate species give loud calls. Lifetime changes in loud calls may be due to either age or social changes. We examined loud call characteristics, loud call production and levels of fecal testosterone among 4 life-phases of male Thomas langurs (Presbytis thomasi): all-male band (AMB), early, middle, and late life-phase in mixed-sex groups. Discriminant analyses showed that a high percentage of loud calls could be assigned correctly to the proper life-phase. The most significant change in loud call characteristics is an increase in tonal units and duration from the AMB to the early life-phase, accompanied by a decrease in non-tonal units. Since adult AMB males have a similar age to that of early life-phase males, we suggest that social rather than age-related changes underlie the loud call differences between AMB males and early life-phase males. This could also be related to the increase in testosterone levels from the AMB to the early life-phase. In addition, we postulate that females may use loud call characteristics as a cue to choose between young and old males once they decided to leave their current male, and possibly also as a cue to decide to leave their current male as he enters his late life-phase.     

Call Variation in Tufted Titmice (Baeolophus bicolor) in a Distress Context: Potential Sex Differences

Tufted titmice, Baeolophus bicolor, produce calls in the contexts related to threat and approach of, and capture by, a predator. In titmice, these calls transition from the chick‐a‐dee call, used in a wide range of social contexts, to ‘distress’ calls that are produced by birds when captured and held by a predator or human observer. A recent study indicated that titmice modify the note composition of their calls in the presence of such threatening stimuli. Here, we tested whether female and male titmice differed in their calling behavior, as relatively few sex differences have been documented in calls shared by female and male songbirds. Individual titmice were captured in walk‐in treadle traps, and we gradually increased the level of fear or arousal by approaching and finally capturing the bird in the hand. Male titmice produced more chick‐a‐dee calls than females as the level of threat increased, up to the point of capturing the bird in the hand. Furthermore, the note composition of calls produced by males differed from that of calls produced by females. A limitation to our study is that our method did not allow us to rule out the possibility that size or dominance differences, rather than sex, were the main reason for the differences in calling we detected. However, increased size generally was not associated with increased calling. We discuss some possible explanations for variation in distress calling behavior in titmice.