Nonlinear acoustics in pant hoots of common chimpanzees (Pan troglodytes): frequency jumps, subharmonics, biphonation, and deterministic chaos

The pant hoot calls produced by common chimpanzees (Pan troglodytes) are multi-call vocalizations that have figured prominently in investigations of acoustic communication in this species. Although pant hoots are predominantly harmonically structured, they can exhibit an acoustic complexity that has recently been linked to nonlinearity in the vocal-fold dynamics underlying typical mammalian sound production. We examined the occurrence of these sorts of nonlinear phenomena in pant hoot vocalizations, contrasting quieter and lower-pitched "introduction" components with loud and high-pitched "climax" calls in the same bouts. Spectrographic evidence revealed four kinds of nonlinear phenomena, including discrete frequency jumps, subharmonics, biphonation, and deterministic chaos. While these events were virtually never observed during the introduction, they occurred in more than half of the climax calls. Biphonation was by far the most common phenomenon, followed by subharmonics, chaos, and frequency jumps. Individual callers varied in the degree to which their climax calls exhibited nonlinear phenomena, but were consistent in showing more biphonation than other forms. These outcomes show that nonlinear phenomena are routinely present in chimpanzee pant hoots, and help lay the foundation for investigating the function of such events.     

Acoustic analysis of wild chimpanzee pant hoots: Do Kibale Forest chimpanzees have an acoustically distinct food arrival pant hoot?

Recordings were made of 193 pant hoots given by 6 adult males during ad lib sampling over a 16-month period in 1988 and 1989. The presence or absence of a let-down phase, and acoustic measures of the let-down and climax phases of the calls, were compared for different call contexts to determine if an acoustically distinct pant hoot was given uniquely upon arrival at fruiting trees. The greatest proportion of pant hoots with a let-down (LD pant hoots) occurred immediately upon arrival at fruiting trees. However, LD pant hoots also occurred at other times during feeding bouts. The frequency and duration of the first exhaled element of 19 letdown phases were measured, and four measures were made on the highest pitched element of 49 climax phases: duration, maximum and minimum frequencies, and average frequency. No differences were found in these acoustic measures that distinguished calls given immediately upon arrival at a food tree from calls given later during feeding bouts. Thus no evidence was found that an acoustically distinct pant hoot was given uniquely upon arrival at fruiting trees. However, the analyses did suggest that identifiable pant hoot variants are given in different social contexts. The proportion of LD pant hoots decreased in more interactive social contexts, and other acoustic features may be available to distinguish this pant hoot variant at long distances. We suggest that different pant hoot variants might broadcast information specific to social, as opposed to ecological, context. © 1993 Wiley-Liss, Inc.     

Dialects in wild chimpanzees?

Chimpanzees emit a loud, species-typical long distance call known as the pant hoot. Geographic variation between the pant hoots of chimpanzees living in two neighboring populations, the Mahale Mountains and Gombe Stream National Parks, Tanzania, was examined. Analysis of six acoustic features revealed subtle differences in the way chimpanzees from the two populations called. Individuals from the Mahale study site uttered one section of their pant hoots at a faster rate and with shorter elements than animals from Gombe Stream. In addition, individuals at Mahale delivered broader-band, higher pitched “climax” elements than males from Gombe. While genetic factors, anatomical differences, variations in the use of calls at the two sites, and changes in calling over time may account for the variability between populations, we suggest the additional possibility that differences in pant hooting may be due to learning. © 1992 Wiley-Liss, Inc.     

Phrase structure of wild chimpanzee pant hoots: Patterns of production and interpopulation variability

Recordings and behavioral observations of wild chimpanzees were made over a 2-year period in the Kibale National Park, Uganda (Kanyawara and Ngogo communities) to investigate patterns of acoustic variability in long-distance calls. The phrase structures of pant hoots, the species-typical loud call given predominantly by adult males, were analyzed. Analysis revealed that the build-up phrase was frequently absent from the pant hoots of Kibale chimpanzees. By contrast, analysis of published data on Gombe and Mahale chimpanzees (Tanzania) indicated that these animals typically included the build-up in their calls. These results were interpreted as evidence for phrase-level differences between populations in the acoustic morphology of this compound call. Data on age and sex differences in the context of production of pant hoots were analyzed, and their relevance to the possibility that aspects of pant hoot acoustic morphology are learned is discussed. Adult males initiated pant hoots more than subadult males, and adult males joined other pant hooting individuals with pant hoots more than subadult males did. It is suggested that younger males may pant hoot with specific adult males preferentially and that this may affect the development of their pant hoot acoustic morphologies. A peculiar pant hoot variant previously reported from Gombe, the whimper hoot, is described from Kibale. The production of this call by low-ranking individuals suggests that there are social constraints on pant hooting in the chimpanzee community. Ideas concerning the effect of social relationships on interpopulation variability in vocal signals are briefly discussed. © 1996 Wiley-Liss, Inc.     

Geographic variation in the calls of wild chimpanzees: A reassessment

Male chimpanzees produce a species‐typical call, the pant hoot, to communicate to conspecifics over long‐distances. Calls given by males from the well‐known Gombe and Mahale populations typically consist of four different phases: an introduction, build‐up, climax, and let‐down. Recent observations suggest that chimpanzees living in the Kibale National Park, Uganda, consistently give calls that lack a build‐up and are thus qualitatively distinguishable acoustically from those made by other East African conspecifics. We analyzed additional recordings from Mahale and Kibale to re‐examine geographic variation in chimpanzee calls. Results indicate that males from both sites produce pant hoots containing all four parts of the call. Calls made by chimpanzees from the two populations, however, differ in quantitative acoustic measures. Specifically, males at Kibale initiate their calls with significantly longer elements and build‐up over briefer periods at slower rates than individuals from Mahale. Kibale males also deliver acoustically less variable calls than chimpanzees at Mahale. Although climax elements do not differ between populations in any single acoustic feature, discriminant function analysis reveals that acoustic variables can be used in combination to assign calls to the correct population at rates higher than that expected by chance. Ecological factors related to differences in habitat acoustics, the sound environment of the local biota, and body size are likely to account for these observed macrogeographic variations in chimpanzee calls. Am. J. Primatol. 47:133–151, 1999. © 1999 Wiley‐Liss, Inc.     

Wild Chimpanzees Produce Group‐Specific Calls: a Case for Vocal Learning?

Vocal learning, where animals can modify the structure of their vocalizations as a result of experience, has been found in a range of birds and mammals. Although vocal learning is a fundamental aspect of developing spoken language, there is as yet little evidence that vocal learning occurs in primates. Here we examine whether vocal learning may occur in chimpanzees. We analysed whether wild male chimpanzees, Pan troglodytes verus, of four communities living in a similar habitat in the Taï Forest, Côte d'Ivoire, developed community specific pant hoots. If so, we expected males of three contiguous communities to have distinct pant hoots, while pant hoots of males from a fourth, distant community, located 70 km away, should only differ from those of the contiguous communities by chance. Our analysis confirmed these expectations. In addition, the acoustic distances between the pant hoots of pairs of individuals did not correlate with the genetic relatedness of those pairs, where genetic relatedness was determined using nuclear DNA analysis. Thus, neither habitat nor genetic differences accounted for the observation that there were acoustic differences in the pant hoot structure of males living in neighbouring communities, but not in those of males from a distant community. This suggests that chimpanzees may actively modify pant hoots to be different from their neighbours, providing support for the vocal learning hypothesis.     

Selection for acoustic individuality within the vocal repertoire of wild chimpanzees

Individual primates typically produce acoustically distinct calls. To investigate the factors that facilitate the evolution of individual vocal signatures, we examined two components of the call repertoire of chimpanzees: the pant hoot and pant grunt. Pant hoots are long-distance signals whose recipients can be several hundred meters away, while pant grunts are short-range calls given to conspecifics within close visual range. Given their markedly different contexts of emission, we predicted that natural selection would favor the elaboration of individually distinctive acoustic features in pant hoots compared with pant grunts. Analyses of nine acoustic features revealed that pant hoots are more stereotyped within-individuals and variable between-individuals than pant grunts. These data are consistent with the hypothesis that selection may act to encode varying degrees of individuality in different components of the vocal repertoire of a single species.     

Identification of vocalizers by pant hoots,pant grunts and screams in a chimpanzee

Identification of vocalizers was examined using an auditory-visual matching-to-sample task with a female chimpanzee. She succeeded in selecting the picture of the vocalizer in response to various types of vocalizations: pant hoots, pant grunts, and screams. When pant hoots by two chimpanzees were presented as a "duet", she could identify both of the vocalizers. These results suggest that researchers have underestimated the capability of vocalizer identification in chimpanzees. The chimpanzee correctly chose her own pictures in response to her vocalizations only by exclusion, and she did not show vocal self-recognition. The effect of acoustical modification (pitch shift and filtration) on the performance suggested that pitch is an important cue for the vocalizer identification.     

Social,contextual, and individual factors affecting the occurrence and acoustic structure of drumming bouts in wild chimpanzees (Pan troglodytes)

The production of structured and repetitive sounds by striking objects is a behavior found not only in humans, but also in a variety of animal species, including chimpanzees (Pan troglodytes). In this study we examined individual and social factors that may influence the frequency with which individuals engage in drumming behavior when producing long distance pant hoot vocalizations, and analyzed the temporal structure of those drumming bouts. Male chimpanzees from Budongo Forest, Uganda, drummed significantly more frequently during travel than feeding or resting and older individuals were significantly more likely to produce drumming bouts than younger ones. In contrast, we found no evidence that the presence of estrus females, high ranking males and preferred social partners in the caller's vicinty had an effect on the frequency with which an individual accompanied their pant hoot vocalization with drumming. Through acoustic analyses, we demonstrated that drumming sequences produced with pant hoots may have contained information on individual identity and that qualitatively, there was individual variation in the complexity of the temporal patterns produced. We conclude that drumming patterns may act as individually distinctive long‐distance signals that, together with pant hoot vocalizations, function to coordinate the movement and spacing of dispersed individuals within a community, rather than as signals to group members in the immediate audience. Am J Phys Anthropol 156:125–134, 2015 © 2014 Wiley Periodicals, Inc.     

Buttress drumming by wild chimpanzees: Temporal patterning, phrase integration into loud calls, and preliminary evidence for individual distinctiveness

Wild chimpanzees (Pan troglodytes) generate low-frequency sounds that are audible to humans from a distance of at least 1 km away by hitting the buttresses of trees with their hands and feet. This buttress drumming occurs in discrete bouts of rapidly delivered beats that usually accompany “pant hoots,” the species-specific long-distance vocalization. Individual differences in male chimpanzee (P.t. verus) drumming were investigated during a 6-month field study in the Taï National Park, Ivory Coast. Analysis of drumming bouts recorded from six adult males revealed significant differences between individuals in three acoustic features: (1) mean duration of inter-beat interval; (2) mean number of beats per bout; and (3) mean bout duration. Preliminary analysis indicated that individuals differ in their tendency to deliver drum beats in temporally close pairs separated by longer interbeat intervals. Qualitative examination also suggested that individuals may differ in the temporal integration of drumming into the pant hoot vocalization. These results suggest that there may be acoustic cues available for chimpanzees to recognize unseen males by their drumming performances alone. Drumming by Taï chimpanzees was also compared to drumming by chimpanzees (P.t. schweinfurthii) from the Kanyawara study group in Kibale National Park. Uganda. The Kanyawara chimpanzees appeared to drum more often without vocalizing than did the Taï chimpanzees. When they did drum and vocalize together, the Kanyawara chimpanzees appeared to integrate their drumming later into the associated pant hoots than did the Taï chimpanzees. These results suggest the possibility that interpopulation variation exists in chimpanzee buttress drumming.     

人为疼痛刺激下金色中仓鼠幼鼠叫声的发育过程

金色中仓鼠幼鼠可以利用可听声和超声信号与母鼠进行交流,这些声音可以反映个体的寒冷、饥饿、疼痛等不同生理状态和需求。因疼痛诱发的叫声对于维持幼鼠的存活也有着重要意义。本实验通过录制人为疼痛刺激下,不同日龄金色中仓鼠的叫声,分析并比较了5 - 30 日龄金色中仓鼠不同发声信号特征(可听声出现频次、可听声持续时程、可听声主频率、超声出现频次、超声持续时程、超声主频率)的性别差异;同时记录了幼鼠的两种发声随日龄的变化趋势。结果发现:幼鼠两种叫声的各种参数均未表现性二型现象。幼鼠超声发生频次随日龄增加而逐渐减少。而可听声却正相反,随日龄增加而逐渐上升,并在20 日龄时达到最高峰,之后逐渐下降。可听声持续时程也随日龄而增加。综上,在人为疼痛刺激下,随着日龄增加,幼鼠更倾向于使用可听 声而非超声与母兽进行交流。     

Complex Vocal Responses to Conspecific Calls in Whistling Frogs Eleutherodactylus johnstonei: Playback Experiments in the Field

We simulated the presence of an acoustic competitor by broadcasting conspecific playbacks to males of Johnstone's whistling frog, Eleutherodactylus johnstonei, in the field. We broadcast calls that differed in duration (short, typical, and long), dominant frequency (high, typical, and low), and period (short, typical, and long), and analyzed male vocal responses. We tested the hypothesis that males respond by escalating vocally when they are exposed to female‐attractive calls and by ignoring unattractive ones. At the population level, males responded to playbacks in ways that would potentially increase their attractiveness with regard to solo calling: males increased the duration, reduced the dominant frequency, and increased their calling effort (duty cycle), despite an increase in call period. The modification of call duration occurred only in response to playbacks of low‐frequency calls, long calls, and short‐period calls (selective response), while the modification of the dominant frequency was independent of the characteristic of the playback (fixed response). Contrary to the expected, males did not reduce the call period when they were exposed to attractive playbacks. At the ultimate level, the results suggest energy‐saving strategies. In addition, males seem to trade off call period for the avoidance of acoustic interference with attractive calls as calling effort was typically increased by increasing call duration but only rarely by reducing the call period. Interactive playbacks are necessary to better understand the calling strategies of males of E. johnstonei.     

CLASSIFICATION OF DIVERSE CALL TYPES USING CLUSTER ANALYSIS TECHNIQUES

ABSTRACT

We investigated the problem of categorizing the repertoire of a group of highly varied vocalizations. A set of Weddell seal Leptonychotes weddellim-air calls recorded near Davis, Antarctica, were examined. The repertoire size was estimated by first subjectively assigning each call (based on auditory and spectrographic patterns) to one of a large number of provisional call types. A set of frequency, duration and waveform measurements were made on every call. For each provisional call type, the mean value of each of these measures was calculated. These mean values were used to perform Cluster Analyses of the provisional call types. Beginning with calls clustered closest together, the most similar provisional call types were successively amalgamated until further joining would link two clearly dissimilar vocalizations (rising versus falling frequency sweeps in this case). The Weddell seal repertoire contained 12 call types ranging from long sinusoidal upsweeps to growls. This procedure provides a method of estimating the minimum repertoire size of a sample of calls. Dichotomous Sorting using Principal Components Analysis can also be used to categorize calls but will probably be of greater value when applied to finding subdivisions within a single call type.     

A comparison of buttress drumming by male chimpanzees from two populations

Wild chimpanzees (Pan troglodytes) produce low-frequency sounds by hitting the buttresses and/or trunks of trees. This buttress drumming occurs in discrete bouts that may be integrated into the phrase sequence of the chimpanzees long-distance vocalization, the pant hoot. The aim of this study was to investigate whether regional variation exists in the drumming behavior of male chimpanzees from Kibale National Park (Kanyawara community), Uganda, and Taï National Park, Ivory Coast. Recordings were made during a 6-month field season at Taï in 1990, and a 12-month field season at Kanyawara in 1996–1997. Acoustic analysis revealed the following: (1) Kanyawara males drummed significantly less frequently in conjunction with a pant hoot or hoot than did Taï males; (2) drumming bouts by Kanyawara males included significantly fewer beats, and were significantly shorter in duration, than those of Taï males; these differences disappeared when only those bouts produced in conjunction with a call were compared; (3) when Kanyawara chimpanzees did call and drum together, they tended to integrate drumming into the vocalization at a later point than did Taï males; and (4) individual differences in the temporal patterning of drumming bouts were not apparent for Kanyawara males, whereas a previous analysis revealed individual differences among Taï males.     

Geographic Variation in the Long Calls of Male Orangutans (Pongo spp.)

Relatively few data exist on population differences in the vocal behavior of mammals. Geographic variation in calls is of special interest because of the implications for resolving evolutionary and behavioral questions. For example, information on geographic variation in vocalizations complements morphological and molecular data used to infer phylogenetic relationships and provides evidence for the mechanisms underlying call development. A quantitative acoustic analysis of orangutan long calls was undertaken, comparing flanged adult males from four geographically distinct sites across Borneo and Sumatra, revealing consistent differences among the calls of individuals. Long calls produced by orangutans from the four sites in Borneo and Sumatra differ in quantitative acoustic measures. Discriminant function analysis reveals that acoustic variables can be used in combination to assign calls to the correct individual, site and island at rates higher than that expected by chance. Specifically, four acoustic parameters proved reliable for distinguishing among the individuals, between sites, and across the two islands that arguably represent populations from separate species or subspecies. Although Bornean and Sumatran long calls share a repetitive structure and show similar call rates (0.100–0.500 LCs/h) and maximum frequency bands (0.400–1.500 kHz), they differ significantly in the number of pulses per call, call speed, call duration, bandwidth, pulse duration, and dominant frequency. Strong consistency in these acoustic parameters is also seen among males within sites and the observed variation may allow for individual recognition. Individual identification by call structure presumably benefits dispersed orangutans, where individuals characteristically forage independently and both encounters and interactions with signaling males are highly variable and largely dependent on context. Acoustic recognition of callers facilitates the choice of which males to join or avoid, thus allowing receivers to manipulate potential costs and benefits of association.     

Female Preferences for Call Traits and Male Mating Success in the Neotropical Frog Physalaemus enesefae

Female preferences for male call traits may affect male mating success and the evolution of exaggerated secondary sexual traits. We used phonotaxis experiments to examine female preferences in the frog Physalaemus enesefae in relation to variation in male call duration, dominant frequency, intercall interval and amplitude (dB SPL). Females preferred long calls, low and average dominant frequency calls, short intercall intervals and more intense calls. We compared the patterns of female preferences with those of acoustic variation among males to test the prediction that properties with low within‐male variation are associated with stabilizing or weakly directional female preferences, whereas properties with high within‐male variation are associated with directional preferences. Females had weakly directional preferences for the dominant frequency of the call and strongly directional preferences for call duration and call rate. We also determined whether the temporal relationship between calls influenced preferences based on the dominant frequency of the call. Preferences for low‐frequency over high‐frequency calls disappeared when calls partially overlapped. Females preferred the leading call regardless of its dominant frequency. We also investigated mating patterns in the field. There was size‐assortative mating, as male and female body sizes snout‐vent length (SVL) were positively correlated. In addition, differences in the frequency distributions of body length (SVL) between mated and unmated males approached significance; lower SVL classes were underrepresented among mated males. These patterns may reflect female preferences for lower dominant frequency calls, as there is a negative correlation between male mass and the dominant frequency of the call.     

Loud calls ofGalago crassicaudatus andG. garnettii and their relation to habitat structure

Long distance vocalizations have been shown to be good indicators of genetic species in primates. Here the loud calls of two recently identified greater galago taxa —Galago crassicaudatus andG. garnettii — are compared and analyzed statistically. Observed differences in call structures are investigated further as potential indicators of differences in the structures of habitats frequented by the two species. Although the calls share a repetitive structure, and show similar dominant frequency bands (1,000 – 1,500 Hz), they differ significantly in the number of units per call, unit duration, inter-unit interval, highest frequency, lowest frequency, dominant frequency band, first harmonic, and call duration. The duration of theG. crassicaudatus call is more than twice that ofG. garnettii. Strong intraspecific consistency is seen in the most energetic frequency bands (dominant frequency band and first harmonic), and durations of the individual units and inter-unit intervals. Information important to species recognition is thus most likely to be contained in these features. Individual recognition may be encoded in the relative emphasis of higher level harmonics. The frequency structures of the calls will reflect requirements for acoustical transmission in a forest environment, as well as structural constraints imposed by body size. Higher frequencies detected in theG. garnettii call (up to 8,500 Hz) may have a functional significance related to distance estimation, or may simply be a reflection of smaller body size. The greater modulation of theG. garnettii call suggests that its habitat constitutes a denser or more turbulent medium for sound transmission than does the habitat ofG. crassicaudatus.     

Social Factors Influence the Acoustic Variability in the Long-distance Calls of Male Chimpanzees

Acoustic variability in the species-typical long-distance calls of male chimpanzees was investigated. Analysis of 13 acoustic features revealed that calls varied more within than between individuals. Although only a limited amount of acoustic variability was attributable to different populations, discriminant-function analysis confirmed that males from two populations produce acoustically distinguishable calls. Additional investigation suggested that social factors may contribute to the patterns of acoustic variation both between and within individuals. Matrix-permutation tests revealed a positive association between the amount of time males spent together and a measure of call similarity. Vocal similarities between individuals appeared to result from a dynamic process involving chorusing behaviour: males matched the acoustic characteristics of each other's vocalizations when calling together. Chorusing may also affect the degree of within-individual acoustic variation in calls. Males who chorused often with others produced more variable calls than individuals who chorused less often or called alone.     

Communication of male quality in owl hoots

The evolution of communication through intrasexual selection is expected to lead signalers to transmit honest information on their fighting ability. Here we studied the information encoded in the acoustic structure of the territorial calls of a nocturnal raptor. During territorial contests, male scops owls give hoots composed of a downward frequency shift followed by a stable plateau. We found that the frequency of the hoot was negatively correlated with the body weight of the vocalizer. We shifted the frequency contour of natural hoots in order to create resynthesized calls corresponding to individuals of varying body weight and used these stimuli in playback experiments simulating an intrusion into the territory of established breeders. Territory owners responded less intensely when they heard hoots simulating heavier intruders, and males with heavier apparent weight tended to give hoots with a lower plateau in response to playbacks simulating heavier intruders.     

Fruit Finding by Mangabeys (Lophocebus albigena): Are Monitoring of Fig Trees and Use of Sympatric Frugivore Calls Possible Strategies?

Frugivorous forest primates face a continual challenge to locate ripe fruit due to the poor visibility characterizing a heavily vegetated habitat and the spatial and temporal unpredictability of their fruit sources. We present two hypotheses regarding fruit finding in gray-cheeked mangabeys (Lophocebus albigena). The first hypothesis is that mangabeys monitor nonfruiting fig trees by visiting and checking them for fruit at a higher rate than control trees that do not produce preferred fruit. We test this hypothesis by comparing rates of visitation to focal fig trees and control trees. The second hypothesis is that mangabeys use sympatric frugivore loud calls to locate fruit sources. We test this hypothesis (1) observationally, by comparing the rates at which mangabeys visit calling sites of sympatric frugivores and matched control areas; and (2) experimentally, by following mangabey responses to playbacks of tape-recorded calls: the black-and-white-casqued hornbill (Bycanistes subcylindricus) long call, the great blue turaco (Corythaeola cristata) rattling kok, the adult male mangabey whoopgobble, and the chimpanzee (Pan troglodytes) pant hoot. We tested the hypotheses via data from a single group of mangabeys in the Kibale National Park, Uganda. There is no evidence that mangabeys monitor fig trees for the presence of fruit, but they may use the calls of hornbills to locate fruit. Statistical evidence that mangabeys use conspecific whoopgobbles and chimpanzee pant hoots in fruit finding is lacking, though anecdotal observations suggest this possibility. There is no evidence for use of turaco calls in fruit finding.