Vocal Bouts Research Articles

Vocal-visual combinations in wild chimpanzees

Living organisms throughout the animal kingdom habitually communicate with multi-modal signals that use multiple sensory channels. Such composite signals vary in their communicative function, as well as the extent to which they are recombined freely. Humans typically display complex forms of multi-modal communication, yet the evolution of this capacity remains unknown. One of our two closest living relatives, chimpanzees, also produce multi-modal combinations and therefore may offer a valuable window into the evolutionary roots of human communication. However, a currently neglected step in describing multi-modal systems is to disentangle non-random combinations from those that occur simply by chance. Here we aimed to provide a systematic quantification of communicative behaviour in our closest living relatives, describing non-random combinations produced across auditory and visual modalities. Through recording the behaviour of wild chimpanzees from the Kibale forest, Uganda we generated the first repertoire of non-random combined vocal and visual components. Using collocation analysis, we identified more than 100 vocal-visual combinations which occurred more frequently than expected by chance. We also probed how multi-modal production varied in the population, finding no differences in the number of visual components produced with vocalisations as a function of age, sex or rank. As expected, chimpanzees produced more visual components alongside vocalizations during longer vocalization bouts, however, this was only the case for some vocalization types, not others. We demonstrate that chimpanzees produce a vast array of combined vocal and visual components, exhibiting a hitherto underappreciated level of multi-modal complexity.

The use of vocal coordination in male African elephant group departures: evidence of active leadership and consensus.

Group-living animals engage in coordinated vocalizations to depart from a location as a group, and often, to come to a consensus about the direction of movement. Here, we document for the first time, the use of coordinated vocalizations, the "let's go" rumble, in wild male African elephant group departures from a waterhole. We recorded vocalizations and collected behavioral data as known individuals engaged in these vocal bouts during June-July field seasons in 2005, 2007, 2011, and 2017 at Mushara waterhole within Etosha National Park, Namibia. During departure events, we documented which individuals were involved in the calls, the signature structure of each individual's calls, as well as the ordering of callers, the social status of the callers, and those who initiated departure. The "let's go" rumble was previously described in tight-knit family groups to keep the family together during coordinated departures. Male elephants are described as living in loose social groups, making this finding particularly striking. We found that this vocal coordination occurs in groups of closely associated, highly bonded individuals and rarely occurs between looser associates. The three individuals most likely to initiate the "let's go" rumble bouts were all highly socially integrated, and one of these individuals was also the most dominant overall. This finding suggests that more socially integrated individuals might be more likely to initiate, or lead, a close group of associates in the context of leaving the waterhole, just as a high-ranking female would do in a family group. The fact that many individuals were involved in the vocal bouts, and that departure periods could be shorter, longer, or the same amount of time as pre-departure periods, all suggest that there is consensus with regard to the act of leaving, even though the event was triggered by a lead individual.

Who is calling: proof of concept for the use of laser Doppler vibrometry in identifying individual callers within African elephant vocalization bouts

Who is calling: proof of concept for the use of laser Doppler vibrometry in identifying individual callers within African elephant vocalization bouts

Structure and functions of Yellow-breasted Boubou (Laniarius atroflavus) solos and duets.

BackgroundBirds have extremely well-developed acoustic communication and have become popular in bioacoustics research. The majority of studies on bird song have been conducted in the temperate zones where usually males of birds sing to attract females and defend territories. In over 360 bird species mostly inhabiting the tropics both males and females sing together in duets. Avian duets are usually formed when a male and female coordinate their songs. We focused on a species with relatively weakly coordinated duets, with male solo as the prevailing vocalisation type.MethodsInstead of analysing a set of recordings spread over a long time, we analysed whole day microphone-array recordings of the Yellow-breasted Boubou (Laniarius atroflavus), a species endemic to West African montane rainforests. We described the structure of the solo and duet vocalisations and temporal characteristics of daily activity based on 5,934 vocal bouts of 18 focal pairs and their neighbours.ResultsBirds had small, sex specific repertoires. All males shared three types of loud whistles functioning as song type repertoires in both solos and duets. Females vocalised with five types of harsh, atonal notes with a more variable and usually lower amplitude. Three of them were produced both as solos and in duets, while two seem to function as alarm and excitement calls given almost exclusively as a solo. Solos were the most common vocalisation mode (75.4%), with males being more vocally active than females. Duets accounted for 24.6% of all vocalisations and in most cases were initiated by males (81%). The majority of duets were simple (85.1%) consisting of a single male and female song type, but altogether 38 unique duet combinations were described. Males usually initiated singing at dawn and for this used one particular song type more often than expected by chance. Male solo and duet activities peaked around dawn, while female solos were produced evenly throughout the day.DiscussionYellow-breasted Boubou is a duetting species in which males are much more vocal than females and duetting is not a dominating type of vocal activity. Duet structure, context and timing of daily production support the joint resource defence hypothesis and mate guarding/prevention hypotheses, however maintaining pair contact also seems to be important. This study provides for the first time the basic quantitative data describing calls, solos and duet songs in the Yellow-breasted Boubou.

Behavioural and physiological responses of West African Dwarf Goat dams and kids subjected to short-term separation

Abstract Nineteen West African Dwarf (WAD) goats were used to investigate the physiological and behavioural responses of dams and kids to short-term separation. The dams were naturally mated with bucks and after parturition the kids remained with their respective dams for 5 weeks. Thereafter, the dams were separated from their kids for 10 minutes / week for three weeks (week 5 – 7). Physiological indicators, namely, eye temperature (ET), heart rate (HRT) and blood glucose (GLUC) were taken from each dam, while the ET and HRT were taken from the kids before and after the separation. The behaviours of the dams and kids were recorded during the separation period at the 7th week. Changes (before minus after) in the physiological parameters (ET, HRT and GLU) for the three weeks were analysed using repeated measures ANOVA while the behavioural data were analysed using non parametric test (SPSS statistical package). The ΔGLUC of WAD dams was greater at the 5th than 7th week. At the 5th week also, the ΔET was greater in dams with single kids than those with twins. Litter size did not influence the behaviour of the dams during separation. A significant correlation was established between ΔHRT and urination in dams. Although sex of the kids had no significant effect on both the physiological and behavioural indicators monitored, negative correlations were established between vocalization bouts and escape attempts (r = −0.516, P < 0.01), duration of vocalisation and escape attempts (r = −0.427, P < 0.05). In conclusion, only WAD dams showed physiological responses indicative of stress during the period of separation.

Interactive vocal communication at the nest by parent Great Tits Parus major

Although most bird species show monogamous pair bonds and bi‐parental care, little is known of how mated birds coordinate their activities. Whether or not partners communicate with each other to adjust their behaviour remains an open question. During incubation and the first days after hatching, one parent – generally the female – stays in the nest for extended periods, and might depend on acoustic communication to exchange information with its mate outside. The Great Tit Parus major is an interesting study system to investigate intra‐pair communication at the nest because males address songs to their mate while she is in the nest cavity, and females answer the male from the cavity with calls. However, the function of this communication remains unknown. In this study, we recorded the vocalizations and observed the resulting behaviour of Great Tit pairs around the nest at different breeding stages (laying, incubation and chick‐rearing). We observed vocal exchanges (vocalization bouts, alternated on the same tempo, between the female inside the nest and her male outside) in three contexts with different outcomes: (1) the female left the nest, (2) the male entered the box with food, and the female then used specific call types, (3) mates stopped calling but did not leave or enter the nest. The structure of vocal exchanges was globally stable between contexts, but females used calls with an up‐shifted spectrum during exchanges, at the end of which they left the nest or the male entered the nest. Birds vocalized more and at higher tempo during exchanges that ended up in feeding inside the nest. Birds also vocalized more during exchanges taking place during laying – a period of active mate guarding – than during incubation. We conclude that vocal exchanges could signal the females’ need for food and the males’ mate guarding behaviour, and discuss other possible functions of this communication.

Tawny owl vocal activity is constrained by predation risk

The vocal behaviour of birds may be influenced by many factors, including the risk of being detected by a predator. In Doñana Protected Area, the tawny owl co‐exists alongside its intraguild predator, the eagle owl Bubo bubo. We considered four scenarios to study the vocal behaviour of tawny owls at dusk by analysing: A) the calling rate of all males in 29 sites; B) the calling rate at dusk of males living within the home range of the intraguild predator; C) the calling rate of males living within the home range of the intraguild predator between 60 and 90 min after sunset; and D) the duration of male vocal bouts in visits where eagle owls have called. In scenario A we found that only the number of conspecific males affected the calling rate of tawny owls. In scenario B we observed that the presence of an eagle owl calling constrained the calling rate of the intraguild prey. In scenario C we found that this effect seemed mostly associated to a contemporaneous detection of the intraguild predator’s calls. Finally, in scenario D we found no significant effects on bout duration. These results seem to indicate that tawny owls use their intraguild predator’s calls as a cue to assess predation risk, and then adjust their vocal behaviour in order to minimize predation risk by a predator that may locate its prey by its vocalizations.

Engineered Deafness Reveals That Mouse Courtship Vocalizations Do Not Require Auditory Experience

Auditory experience during development is necessary for normal language acquisition in humans. Although songbirds, some cetaceans, and maybe bats may also be vocal learners, vocal learning has yet to be well established for a laboratory mammal. Mice are potentially an excellent model organism for studying mechanisms underlying vocal communication. Mice vocalize in different social contexts, yet whether they learn their vocalizations remains unresolved. To address this question, we compared ultrasonic courtship vocalizations emitted by chronically deaf and normal hearing adult male mice. We deafened CBA/CaJ male mice, engineered to express diphtheria toxin (DT) receptors in hair cells, by systemic injection of DT at postnatal day 2 (P2). By P9, almost all inner hair cells were absent and by P16 all inner and outer hair cells were absent in DTR mice. These mice did not show any auditory brainstem responses as adults. Wild-type littermates, also treated with DT at P2, had normal hair cells and normal auditory brainstem responses. We compared the temporal structure of vocalization bouts, the types of vocalizations, the patterns of syllables, and the acoustic features of each syllable type emitted by hearing and deaf males in the presence of a female. We found that almost all of the vocalization features we examined were similar in hearing and deaf animals. These findings indicate that mice do not need auditory experience during development to produce normal ultrasonic vocalizations in adulthood. We conclude that mouse courtship vocalizations are not acquired through auditory feedback-dependent learning.

Antiphonal vocal bouts associated with departures in free-ranging African elephant family groups (Loxodonta africana)

We describe the interactive nature of vocalizations emitted by African elephant (Loxodonta africana) family groups while visiting waterholes. Despite being in close visual contact with each other, individuals called interactively within a series of overlapping or antiphonal vocal bouts that increased significantly while departing from the waterhole. After initiating departure from the waterhole, elephants in this study increased their calling rate and their production of overlapping vocal bouts. The majority of calls either overlapped or occurred within 1.5 seconds of another call as part of an antiphonal bout, rather than as isolated calls. The departure of larger herds was accompanied by a greater number of calling bouts. The increase in interactive antiphonal bouts during departure might serve to facilitate group coordination and cohesion, as well as possibly reinforce social bonds. The longer repeated bouts could also facilitate eavesdropping by distant elephants by boosting signal detection since the repetition of these longer calls may yield an increase in the signal-to-noise ratio (SNR) that reduces the noise floor for better longer distance communication.

Development of social vocalizations in mice.

Adult mice are highly vocal animals, with both males and females vocalizing in same sex and cross sex social encounters. Mouse pups are also highly vocal, producing isolation vocalizations when they are cold or removed from the nest. This study examined patterns in the development of pup isolation vocalizations, and compared these to adult vocalizations. In three litters of CBA/CaJ mice, we recorded isolation vocalizations at ages postnatal day 5 (p5), p7, p9, p11, and p13. Adult vocalizations were obtained in a variety of social situations. Altogether, 28,384 discrete vocal signals were recorded using high-frequency-sensitive equipment and analyzed for syllable type, spectral and temporal features, and the temporal sequencing within bouts. We found that pups produced all but one of the 11 syllable types recorded from adults. The proportions of syllable types changed developmentally, but even the youngest pups produced complex syllables with frequency-time variations. When all syllable types were pooled together for analysis, changes in the peak frequency or the duration of syllables were small, although significant, from p5 through p13. However, individual syllable types showed different, large patterns of change over development, requiring analysis of each syllable type separately. Most adult syllables were substantially lower in frequency and shorter in duration. As pups aged, the complexity of vocal bouts increased, with a greater tendency to switch between syllable types. Vocal bouts from older animals, p13 and adult, had significantly more sequential structure than those from younger mice. Overall, these results demonstrate substantial changes in social vocalizations with age. Future studies are required to identify whether these changes result from developmental processes affecting the vocal tract or control of vocalization, or from vocal learning. To provide a tool for further research, we developed a MATLAB program that generates bouts of vocalizations that correspond to mice of different ages.

Review: Relevance of stimuli used in canine behavioral testing with regard to proximal causality of dog bites

s 61 having established that the number of dogs in the kennel (n 5 8-13) did not correlate with measures of noise intensity or habituation. Mean time taken for the dogs to habituate (692.5s vs 358.8s) and number of vocalization bouts (29 vs 13.75) were both significantly (p , 0.05) greater in the transparent conditions. There was no difference between the two conditions in the mean volume (58.61dB vs 60.23dB) or peak volume (85.7 vs 88.2dB) during habituation. The long term effects and the general applicability of this intervention have not been assessed, but deserve investigation as they might offer a simple way to reduce the amount of barking in kennels.

Does the owner provide a secure base? Behavioral and heart rate response to a threatening stranger and to separation in dogs

mother–pup intraspecific attachment behavior in the domes-tic dog (Canis familiaris).One hundred forty-five puppy–mother pairs of differentbreeds were tested using the Strange Situation Test. Puppieswere45-55days old at time of testing. The test consisted of 7consecutive 3-minute episodes in which the pup was placedin an unfamiliar environment, introduced to an unfamiliarwoman, and subjected to separation from the mother. Thebehavior of each dyad was videorecorded, and 22 mutuallyexclusive behaviors were scored using 5-second point sam-pling. Furthermore, proximity and physical contact betweenthe mother and the pup were recorded, and bouts of vocal-izations were scored ad libitum. Factor analysis, with Eigen-values .1, varimax rotation, and factor loading .0.50, wascarried out on the puppies’ behavior.Factor analysis extracted 8 principal dimensions: (1) ‘‘affil-iationtowardhumans’’(i.e.,positive/playfulinteractionsuchas play, following and greeting behaviors); (2) ‘‘humancontact seeking’’ (i.e., approaching, keeping contact, andlicking the person); (3) ‘‘self-confidence,’’ which includedplaying alone with toys in opposition to being orientedtoward the mother; (4) ‘‘distress/protest,’’ consisting ofreactions such as remaining oriented toward and scratchingthe door; (5) ‘‘affiliation toward the mother’’ (i.e., positive/playful interaction); 6) ‘‘mother contact seeking’’ (i.e.,behaviors pertaining to nurturing demands: licking, follow-ing, suckling); (7) ‘‘apprehension toward humans’’ (i.e.,approaching the mother, avoiding and orienting away fromhumans); and (8) ‘‘exploration’’ (i.e., visual and olfactoryexploration of the room, and exploration of toys).Results demonstrated that, as with human infants, the SSTis a valuable tool for studying attachment in pups. Pupsshowed a whole behavioral repertoire indicating a ‘‘securebase’’ effect (playing with toys and mother orientation in asingle factor with opposite weightings), proximity seekingtoward the mother, and distress upon separation.Key words: puppies; attachment; affectional bonds; StrangeSituation Test

Treatment of Tourette’s Syndrome With Finasteride

Back to table of contents Previous article Next article Letters to the EditorFull AccessTreatment of Tourette’s Syndrome With FinasterideMARCO BORTOLATO M.D., Ph.D.ANTONELLA MURONI M.D.FRANCESCO MARROSU M.D.,MARCO BORTOLATO M.D., Ph.D.Search for more papers by this authorANTONELLA MURONI M.D.Search for more papers by this authorFRANCESCO MARROSU M.D.Search for more papers by this author,Published Online:1 Dec 2007https://doi.org/10.1176/appi.ajp.2007.07060978AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InEmail To the Editor: The marked male predominance of Tourette’s syndrome suggests that androgens may play a key role in the pathophysiology of this disorder (1) . Accordingly, androgen receptor antagonists, such as flutamide, significantly attenuate Tourette’s syndrome symptoms (2) , yet their efficacy is hindered by severe side effects. A valid alternative to reduce androgen brain signaling may be afforded by inhibitors of 5-alpha-reductase (5-AR), the main rate-limiting enzyme in androgen metabolism. Thus, we tested the efficacy of finasteride, the prototypical 5-AR inhibitor, in a Tourette’s syndrome patient who was unresponsive to traditional therapy. Finasteride is approved for the treatment of benign prostatic hyperplasia and alopecia; it is psychoactive (3) and produces very limited side effects. A 34-year-old man with a 25-year history of severe Tourette’s syndrome was referred to our service following a precipitation of his clinical conditions. His symptoms included self-injuring motor tics (i.e., glass smashing and knuckle rubbing against rough surfaces), explosive bouts of complex vocalizations, stereotyped coprolalic utterances, ritual behaviors, aggressive and contamination-theme obsessions, cleaning and checking compulsions, and excessive sexual drive. Magnetic resonance imaging and laboratory tests were normal. His current treatment—initiated 2 years before and included pimozide (4 mg/day), clomipramine (37.5 mg/day), chlorpromazine (25 mg/day), and lorazepam (7.5 mg/day)—had only resulted in a transient, slight decrease of motoric compulsions and anxiety. After obtaining informed consent, we added finasteride (5 mg/day) to his current treatment and periodically assessed his symptoms by means of the Yale Global Tic Severity Scale and Yale-Brown Obsessive Compulsive Scale. Finasteride gradually reduced both motor and phonic tics. Because of a misunderstanding about the regimen duration, the patient discontinued treatment at week 18. Three days later, he called our service complaining of a dramatic exacerbation in Tourette’s syndrome symptoms. Notably, the prompt reinstatement of finasteride led to a clear clinical improvement. After 28 weeks of treatment, finasteride led to a dramatic reduction in Yale Global Tic Severity Scale ( Figure 1 ) and Yale-Brown Obsessive Compulsive Scale scores (obsessive score: 58.3% initial values; compulsive score: 38.4% initial values). The patient also reported a normalized sex drive, enhanced mood and life quality, and no untoward effects. Figure 1. Effects of Finasteride Treatment on Severity of Tics in a Patient With Tourette’s Syndrome aa Yale Global Tic Severity Scale scores of total severity, total phonic tics, and total motor tics during the first 28 weeks of therapy. In humans, finasteride inhibits mainly the isozyme 5-AR2, the activity of which is potently enhanced by androgens in the adult brain. Abnormal levels of brain 5-AR2 androgens, such as the potent neuroactive androgen dihydrotestosterone, may contribute to Tourette’s syndrome pathophysiology. Further studies, including double-blind clinical trials, are needed to fully evaluate the therapeutic potential of finasteride in Tourette’s syndrome.Monserrato, ItalyThe authors report no competing interests.This letter (doi: 10.1176/appi.ajp.2007.07060978) was accepted for publication in August 2007.Reprints are not available; however, Letters to the Editor can be downloaded at http://ajp.psychiatryonline.org.

Cepstral coefficients and hidden Markov models reveal idiosyncratic voice characteristics in red deer (Cervus elaphus) stags

Bouts of vocalizations given by seven red deer stags were recorded over the rutting period, and homomorphic analysis and hidden Markov models (two techniques typically used for the automatic recognition of human speech utterances) were used to investigate whether the spectral envelope of the calls was individually distinctive. Bouts of common roars (the most common call type) were highly individually distinctive, with an average recognition percentage of 93.5%. A "temporal" split-sample approach indicated that although in most individuals these identity cues held over the rutting period, the ability of the models trained with the bouts of roars recorded early in the rut to correctly classify later vocalizations decreased as the recording date increased. When Markov models trained using the bouts of common roars were used to classify other call types according to their individual membership, the classification results indicated that the cues to identity contained in the common roars were also present in the other call types. This is the first demonstration in mammals other than primates that individuals have vocal cues to identity that are common to the different call types that compose their vocal repertoire.

Babbling behavior in the sac-winged bat (Saccopteryx bilineata)

Infant babbling in humans and a few other primates plays an important role in allowing the young to practice the adult vocal repertoire during early behavioral development. Vocalizations uttered during babbling resemble, to some degree, the acoustic structure of adult vocalizations and are often produced in long bouts independent of any social context. Similar behavior, termed subsong or plastic song, is known from a variety of songbirds. Here, we show that pups of the sac-winged bat (Saccopteryx bilineata), a species with an unusually large vocal repertoire, produce renditions of all known adult vocalization types during bouts of vocalizations, which appear to be independent of a distinct social context. Babbling occurs in pups of both sexes, even though only adult males, not females, utter all different vocalization types produced in infancy. To our knowledge, this is the first evidence of babbling in a nonprimate mammal and suggests that infant babbling may be necessary for the ontogeny of complex vocal repertoires.

Siamang gibbons exceed the saccular threshold: intensity of the song of Hylobates syndactylus.

Measurements are reported of the intensity of the siamang gibbon loud call obtained from the vocal bouts of three family groups at Twycross Zoo, UK. Across 25 samples the maximum intensity ranged from 95 to 113 dB SPL (linear frequency-weighting and fast time-weighting) and exhibited three frequency modes of 250-315 Hz, 630-800 Hz and 1.2-1.6 kHz. The lowest frequency mode, which may correspond to the "boom" sound produced by resonance of the siamang inflated vocal sac, had a mean maximum intensity of 99 dB SPL. These values, which are in excess of the saccular acoustic threshold of about 90 dB at 300 Hz for air conducted sound, suggest that primate loud calls recruit a primitive mode of acoustic sensitivity furnished by the sacculus. Thus reproductive vocal behavior of primates may be influenced by a primitive acoustical reward pathway inherited from a common ancestor with anamniotes. In humans such a pathway could explain the compulsion for exposure to loud music.

Information entropy analysis of leopard seal vocalization bouts

Leopard seals (Hydrurga leptonyx) are solitary pinnipeds who are vocally active during their brief breeding season. The seals produce vocal bouts consisting of a sequence of distinct sounds, with an average length of roughly ten sounds. The sequential structure of the bouts is thought to be individually distinctive. Bouts recorded from five leopard seals during 1992–1994 were analyzed using information theory. The first-order Markov model entropy estimates were substantially smaller than the independent, identically distributed model entropy estimates for all five seals, indicative of constraints on the sequential structure of each seal’s bouts. Each bout in the data set was classified using maximum-likelihood estimates from the first-order Markov model for each seal. This technique correctly classified 85% of the bouts, comparable to results in Rogers and Cato [Behaviour (2002)]. The relative entropies between the Markov models were found to be infinite in 18/20 possible cross-comparisons, indicating there is no probability of misclassifying the bouts in these 18 comparisons in the limit of long data sequences. One seal has sufficient data to compare a nonparametric entropy estimate with the Markov entropy estimate, finding only a small difference. This suggests that the first-order Markov model captures almost all the sequential structure in this seal’s bouts.

Variations in the arrangement of South American sea lion (<I>Otaria flavescens</I>) male vocalizations during the breeding season: patterns and contexts

We analysed whether South American sea lions (Otaria e avescens ) varied the syntax or arrangement of vocalizations (the order in which calls were produced) according to di Verent social contexts. Three male calls that formed a progression of increasingly aggressive displays (growl<bark<highpitched call) were studied in a breeding colony at Peni nsula Valde s. We found that: (a) growls and barks had higher probabilities of emission than high-pitched calls, (b) vocal bouts generally were initiated by growls, (c) the transitions most likely to occur were growl-bark and bark-growl, and (d) the number of male-male agonistic interactions (highpitched call after growl, bark after growl) and the number of neighbour males (growl after highpitched call) a Vected some transitions between call types. The baseline vocal display of males consists of a sequence of growls and barks given in succession (e.g., growl‐ bark‐ growl‐ bark), which can incorporate high-pitched calls during highly aggressive male-male interactions. Vocal arrangement variations could be a strategy to modulate agonistic behaviour during vocal displays and to increase the chances of being detected in noisy breeding colonies.

The costs of singing in nightingales

The costs of singing in birds are poorly understood. One potential type of cost is a metabolic cost of singing. Previous studies have measured short-term changes in oxygen consumption associated with bouts of vocalizations, with equivocal results. In this study, I used an alternative approach to measuring the metabolic cost of singing, by measuring overnight loss of body mass, in male common nightingales, Luscinia megarhynchos, singing at night at different rates. Nightingales were shown not to forage at night. They reached a higher mass at dusk prior to singing more at night, and lost more mass overnight when dusk mass and overnight song rate were high. These results show that singing at night is associated with increased overnight consumption of body reserves, which represents a significant metabolic cost of singing at night. However, the correlation between dusk mass and overnight song rate makes it impossible to determine whether these costs arise from the energetic costs of the singing itself, or from the metabolic costs of the additional body reserves laid down at dusk on nights when song rate was high. There are also likely to be costs associated with accumulating and carrying these extra body reserves during daylight, as well as other potential costs of singing such as an increased risk of predation. These results are consistent with those models of signalling in biology that predict or assume that honest signals are costly. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.

'BABBLING' IN PYGMY MARMOSETS: DEVELOPMENT AFTER INFANCY

AbstractInfant pygmy marmosets (Cebuella pygmaea) are extremely vocal with much of their calling occurring in long sequences of mixed call-types that appears to have several parallels to the babbling of human infants (Elowson et al., 1998b). We refer to this vocal behaviour as Pygmy Marmoset Babbling (PMB) (Elowson et al., 1998a). We followed several of our original subjects beyond infancy to adulthood. Babbling bouts continued to appear through the age of puberty though at a reduced rate from that seen in infancy, but babbling was rarely observed in adults. With increasing age the vocal bouts contained a greater diversity of call types per bout and a decrease in call series duration. In addition, with increasing age there were decreasing proportions of calls that were Adult Variant and Infant calls and an increase in Adult calls. Structural analyses of trills, the most common call type found in vocal bouts, showed increased proportions of well-formed trills and decreased proportions of poorly formed trills with increased age, with different features reaching adult form at different ages. Babbling by juvenile marmosets was associated with increased social interactions with other group members as we had observed with infants. 'Babbling' in both infant and juvenile marmosets might provide vocal practice as well as attract attention from other group members.