BIOACOUSTIC PUBLICATIONS, 1989

ABSTRACT

In order to increase understanding of African elephant vocal communication and to standardise the terminology used to describe vocalisations, this study examined acoustic and temporal characteristics of 983 vocalisations from 2 male and 6 female captive African elephants. Recording collars were used to monitor vocalisations and videotape to simultaneously record behaviour, allowing for unambiguous attribution of sounds to individuals, even in close proximity. Eight acoustically distinct categories of calls were defined in terms of structural characteristics; two of these categories are described for the first time. Low-frequency vocalisations containing infrasonic components were predominant in this localised communication context and showed a gradation of variation in acoustic structure and duration. Most calls were part of temporally closed exchanges between individuals and coincided with short-distance interactions. In addition, male-female choruses and non-musth rumbles from males were documented, suggesting that the African elephant vocal repertoire may be more complex than previously reported.     

Variable Food Begging Calls Are Harbingers of Vocal Learning

Vocal learning has evolved in only a few groups of mammals and birds. The developmental and evolutionary origins of vocal learning remain unclear. The imitation of a memorized sound is a clear example of vocal learning, but is that when vocal learning starts? Here we use an ontogenetic approach to examine how vocal learning emerges in a songbird, the chipping sparrow. The first vocalizations of songbirds, food begging calls, were thought to be innate, and vocal learning emerges later during subsong, a behavior reminiscent of infant babbling. Here we report that the food begging calls of male sparrows show several characteristics associated with learned song: male begging calls are highly variable between individuals and are altered by deafening; the production of food begging calls induces c-fos expression in a forebrain motor nucleus, RA, that is involved with the production of learned song. Electrolytic lesions of RA significantly reduce the variability of male calls. The male begging calls are subsequently incorporated into subsong, which in turn transitions into recognizable attempts at vocal imitation. Females do not sing and their begging calls are not affected by deafening or RA lesion. Our results suggest that, in chipping sparrows, intact hearing can influence the quality of male begging calls, auditory-sensitive vocal variability during food begging calls is the first step in a modification of vocal output that eventually culminates with vocal imitation.     

DEVELOPMENT OF VOCALISATIONS IN NESTLING AND FLEDGLING HOUSE WRENS IN NATURAL POPULATIONS

ABSTRACT

We conducted a field study of the ontogeny of vocal signals in the house wren Troglodytes aedon during the nestling and fledgling phases of life. We did spectrographic analyses and quantification of the developmental changes that occurred in the acoustic features of the vocalisations. Evidence of progress to adult-like vocal patterns was of two types. First, nestling calls changed into a harsh-sounding call that resembles the adult chatter call, functionally a warning call. Second, fledglings also uttered subsong, and these vocalisations were similar to notes typical of adult male song. When the vocalisations produced by developing young were broken down into their constituent vocal features, we found that the time course of development was not strictly linear. Instead of a unidirectional change through the course of nestling and fledgling life, the trajectories of the vocal features fluctuated through time and sometimes exhibited abrupt changes. These sudden shifts occurred during nestling life as well as at the time of fledging. We speculate on the possible causes of these abrupt transitions. Changes in acoustic features upon fledging appear to be linked to new social functions.     

BIOACOUSTIC PUBLICATIONS, 1988

ABSTRACT

We examined vocalisations of a solitary subterranean rodent, the Silvery Mole-rat Heliophobius argenteocinereus (Bathyergidae). Seven true vocalisations and one mechanical vocalisation were identified. The main frequencies of the analysed sounds (0.34–13.17 kHz) match to a great extent the frequency range suitable for transmission in underground burrows. Due to the narrow frequency range of vocalisations, motivation is predominantly expressed by the rate of tonality rather than by frequency changes. The vocal repertoire of the Silvery Mole-rat perfectly matches to Morton's MS rules, i.e. that low-frequency and harsh vocalisations indicate hostility whereas high tonal calls signalise appeasement or fear. In comparison with social species, this solitary bathyergid produces fewer calls. It lacks contact and alarm calls, but has a rich repertoire of mating calls (mating ends with duet vocalization of male and female). Acoustic signals seem to play a major role in lowering natural aggressiveness during the mating period.     

Development of vocal behaviour in Peking ducklings

Vocal communication appears to play an important role in maintaining group cohesion in broods of Peking ducklings (Anas platyrhynchos). In order to describe the development of the vocal repertoire of the young, the present study examined the vocalizations of six ducklings from several hours before hatching through 48 h posthatching. Vocalizations were recorded in standardized situations in the laboratory, including the presence of conspecific peers, exposure to maternal calls, and social isolation. A major methodological aim of the present study was to determine whether the vocal repertoire of the ducklings would sort itself on objectively measured acoustic features without the necessity of experimenter preclassification (as has been relied upon in the past). This objective procedure produced two acoustically distinct (and conventional) types: (a) contentment calls, which have short note durations, fast repetition rates, and low pitch, and are elicited by the presence of peers and/or the maternal call; (b) distress calls, with longer note durations, slower repetition rates, and higher pitch, which are uttered in social isolation and emerge in mature form only after hatching. A simple physiological model based on respiratory activity is proposed to account for the acoustic variation between the two vocalization types.     

Vocal behavior of Great Curassows,a vulnerable Neotropical bird

ABSTRACT The Cracidae rank among the most threatened families of Neotropical birds, and studies of their vocal behavior may help guide conservation and monitoring efforts. We describe the vocal behavior of Great Curassows (Crax rubra), a little‐studied Cracid species currently listed as vulnerable. From 2008 to 2010, we recorded curassows in northwest Costa Rica using both handheld and automated digital recorders. Analysis of recordings revealed that Great Curassows had a vocal repertoire of five call types. Yip and bark calls are sex‐specific alarm calls of short duration (0.12 and 0.08 s, respectively). The descending whistle is a longer duration alarm call (2.18 s) produced primarily by males. The snarl is a short call (0.67 s) associated with a threat display produced by adults with dependent young. The boom call was the most common Great Curassow vocalization, and was given only by males. Boom calls are long (8.86 s), low‐frequency (<150 Hz), multisyllable calls comprised of four stereotyped phrases. Great Curassows often uttered boom calls well before dawn, with a peak in activity at dawn and the hours following. Males produced bouts of repeated boom calls that lasted an average of 35 min, but sometimes continued for more than 5 h. Boom calls were given from February to June, with a peak in late April and early May when breeding begins. Discriminant analysis of boom calls of birds from 10 different locations revealed interindividual variation in call structure that may be useful for bioacoustic monitoring of individuals. Our results suggest that automated recorders might provide a way to monitor the abundance of male curassows because their boom calls are given frequently during the period from February to June and can be detected at distances up to 250 m.     

BIOACOUSTIC PUBLICATIONS, 1989

ABSTRACT

Coruros Spalacopus cyanus, social fossorial rodents from Chile, use a complex acoustic repertoire with eleven different true vocalisations and one mechanical sound in various behavioural contexts. The complex of contact calls is particularly well differentiated. Juvenile coruros produced six true vocalisations of which four were structurally identical to adult calls. One vocalisation had components of two adult sounds and one occurred only in juvenile animals. Certain calls from the adult repertoire were lacking. The frequencies of sounds of juveniles were considerably higher than those of adults, with many sounds reaching the ultrasonic range. Nevertheless, pure ultrasonic sounds were not recorded.

The frequencies of the analysed sounds of coruros extended from 0.17 to 20.33 kHz with dominant frequency components between 0.17 and 10 kHz. The acoustic properties of calls are suitable for transmission above and below ground, thus providing further indirect evidence that coruros are not strictly confined to an underground way of life. Indeed, the great variability of frequency ranges, with lower frequencies always being included, reflects a specialisation for communication in variable acoustic environments.

The most distinctive and unique vocalisation of coruros is the long duration musical trilling (lasting up to two minutes), which is a long-distance call emitted in alarm and arousal contexts. Recordings of this call from natural burrows in the field in Chile showed similar structural features to vocalisations from captive colonies in the laboratory.

Our findings provide a further example of matching physical properties of vocalisations to the acoustic conditions of the habitat. However, vocalisations in subterranean rodents consist almost exclusively of short-distance calls, the trilling of coruros being the notable exception. Since the selective pressure of the acoustic environment upon the evolution of short-distance vocalisations is probably minimal, we suggest that during their evolution, subterranean mammals have matched their vocalisations primarily to their hearing range and not directly to the acoustics underground. Hearing probably has been the primary target of natural selection, serving not only for communication but also for detection of predators (and, in carnivores, of prey).     

Detection and vocalisations of three owl species (Strigiformes) in temperate rainforests of southern Chile

Conspecific broadcasts are effective to increase detection of owls. To determine the most appropriate time of the year to survey owls, we played conspecific owl vocalisations monthly in a temperate rainforest of southern Chile. From 12 broadcast points surveyed we recorded detections of Glaucidium nana, Strix rufipes and Tyto alba. Glaucidium nana presented a bimodal detection curve throughout the year and we recorded two regular vocalisations in response to broadcasting: contact pair call and territorial call. Strix rufipes and T. alba both showed a peak of detection between February and May. Strix rufipes presented three vocalisations: territorial call, contact pair call and female contact pair call while T. alba uttered two vocalisations: territorial call and twittering call. We recommend surveys during the end of the breeding season (austral summer–autumn) when detection is higher in most owls. Surveys should also take into consideration the variability of the vocalisations and include covariates in monitoring to evaluate occupancy/detection models.     

Geographic variation of Weddell seal (<Emphasis Type="Italic">Leptonychotes weddellii</Emphasis>) airborne mother–pup vocalisations

Geographic variation of vocal behaviour may be reflective of genetic, cultural and ecological differences between locations. Such differences have been previously reported in six pinnipeds, including Weddell seals (Leptonychotes weddellii). This study investigated whether the acoustic characteristics of airborne Weddell seal mother and pup ‘contact’ calls vary geographically between the Vestfold Hills and McMurdo Sound. From each location, 72 mother and 120 pup calls were analysed, with 11 acoustic characteristics measured. MANOVA and Discriminant function analysis (DFA) identified significant differences in several fundamental frequency characteristics. The cross-validated DFA classified greater than 60% of mother and pup vocalisations to the correct location. For novel calls, the probabilities of correctly classifying these percentages by chance are low. Additionally, ordinal logistic regression identified significant differences in the maximum energy distribution of mother and pup vocalisations. For pups, this variation is likely the result of genetic differences between the two populations. Nevertheless, results support suggestions that, when compared with underwater repertoire differences, airborne within-call differences are less efficient at identifying Weddell seal breeding populations.     

Vocalizations and morphology: interpreting the divergence among populations of Chough Pyrrhocorax pyrrhocorax and Alpine Chough P. graculus

Capsule Differences in vocalizations among populations are mostly explained on morphological bases, but historical factors may have played a significant role in differentiation processes.

Aims To investigate the relationships among vocal and morphological variation in two corvids: Chough and Alpine Chough.

Methods We used data from 11 populations of Chough and seven populations of Alpine Chough spanning the Palearctic distribution of the two species. Three data sets (morphometry, spectrotemporal parameters of trill calls and acoustic repertoire) were analysed and their variation compared with uni- and multivariate techniques.

Results In both species, morphological differences among populations were correlated to spectro-temporal variation of trills; in particular, frequencies of calls were negatively correlated to wing length (an indicator of body size). By considering only co-existing populations of the two species, the magnitude of morphological and spectrotemporal divergence was similar.

Conclusions In both species, birds from populations with similar morphology uttered similar call types and trills with close spectrotemporal features. In particular, larger-sized populations, as expressed by wing length, emitted lower pitched calls. However, the fact that dissimilarities in repertoire and morphology were correlated cannot be explained only by appealing to functional explanations, as the observed intraspecific morphological variability does not seem to be high enough to promote consistent changes in the pool of calls. In this case, historical factors might have contributed to the present pattern of differentiation.     

Vocal communication of tonkean macaques in confined environments

Vocal recordings of one semi-free-ranging group and one captive group of Tonkean macaques (Macaca tonkeana) were used to establish the vocal repertoire of the species. Only the alpha male of the groups uttered a very distinctive loud call. Localization variants of coo calls were found. Alarm calls given by this species were acoustically similar to those by Japanese, rhesus, and long-tailed macaques (M. fuscata, M. mulatta, andM. fascicularis). Adult females uttered a specific variant of vocalizations during sexual morphological changes. The repertoire of agonistic vocalizations was more variable than that of any other macaque species investigated. These characteristics were discussed with reference to previous studies on vocalizations of macaque species.     

Bioacoustical structure and possible functional significance of wing display vocalisation during courtship of the African Orange-bellied Parrot Poicephalus rufiventris

Venuto, V., Bottoni, L. & Massa, R. 2000. Bioacoustical structure and possible functional significance of wing display vocalisation during courtship of the African Orange-bellied Parrot Poicephalus rufiventris. Ostrich 71 (1 & 2): 131–135.

We report here on a bioacoustical and contextual analysis of Orange-bellied Parrot vocalisations recorded in Tarangire National Park, Tanzania. We analysed a total of 154 vocalizations of which 110 were simple calls pertaining to five different types (A and B contact calls, whistle, flight call, and trill call) while 44 were complex calls (wing stretching and wing display songs) totalling three minutes of record. All simple calls examined appeared to be shorter than one second and sexually dimorphic. In addition, the longest and most structured vocalisations lasting 1–5 sec, wing stretching and wing display courtship song, appeared to be complex bioacoustic products in which a number of shorter units used by birds in completely different contexts may be recognised. It is argued that this assemblage of simple calls into a courtship song may have been important in the evolution of parrot mimicry for the search of social contact.     

Imperfect mimicry of host begging calls by a brood parasitic cuckoo: a cue for nestling rejection by hosts?

Coevolutionary interactions between avian brood parasites and their hosts often lead to the evolution of discrimination and rejection of parasite eggs or chicks by hosts based on visual cues, and the evolution of visual mimicry of host eggs or chicks by brood parasites. Hosts may also base rejection of brood parasite nestlings on vocal cues, which would in turn select for mimicry of host begging calls in brood parasite chicks. In cuckoos that exploit multiple hosts with different begging calls, call structure may be plastic, allowing nestlings to modify their calls to match those of their various hosts, or fixed, in which case we would predict either imperfect mimicry or divergence of the species into host-specific lineages. In our study of the little bronze-cuckoo (LBC) Chalcites minutillus and its primary host, the large-billed gerygone Gerygone magnirostris, we tested whether: (1) hosts use nestling vocalizations as a cue to discriminate cuckoo chicks; (2) cuckoo nestlings mimic the host begging calls throughout the nestling period; and (3) the cuckoo begging calls are plastic, thereby facilitating mimicry of the calls of different hosts. We found that the begging calls of LBCs are most similar to their gerygone hosts shortly after hatching (when rejection by hosts typically occurs) but become less similar as cuckoo chicks get older. Begging call structure may be used as a cue for rejection by hosts, and these results are consistent with gerygone defenses selecting for age-specific vocal mimicry in cuckoo chicks. We found no evidence that LBC begging calls were plastic.     

Avian vocalisations: the female perspective

Research on avian vocalisations has traditionally focused on male song produced by oscine passerines. However, accumulating evidence indicates that complex vocalisations can readily evolve outside the traditional contexts of mate attraction and territory defence by male birds, and yet the previous bias towards male song has shaped – and continues to shape – our understanding of avian communication as a whole. Accordingly, in this review we seek to address this imbalance by synthesising studies on female vocalisations from across signalling contexts throughout the Aves, and discuss the implications of recent empirical advances for our understanding of vocalisations in both sexes. This review reveals great structural and functional diversity among female vocalisations and highlights the important roles that vocalisations can play in mediating female-specific behaviours. However, fundamental gaps remain. While there are now several case studies that identify the function of female vocalisations, few quantify the associated fitness benefits. Additionally, very little is known about the role of vocal learning in the development of female vocalisations. Thus, there remains a pressing need to examine the function and development of all forms of vocalisations in female birds. In the light of what we now know about the functions and mechanisms of female vocalisations, we suggest that conventional male-biased definitions of songs and calls are inadequate for furthering our understanding of avian vocal communication more generally. Therefore, we propose two simple alternatives, both emancipated from the sex of the singer. The first distinguishes song from calls functionally as a sexually selected vocal signal, whilst the second distinguishes them mechanistically in terms of their underlying neurological processes. It is clear that more investigations are needed into the ultimate and proximate causes of female vocalisations; however, these are essential if we are to develop a holistic epistemology of avian vocal communication in both sexes, across ecological contexts and taxonomic divides.     

DOCUMENTATION STANDARDS FOR WILDLIFE SOUND RECORDINGS

ABSTRACT

Shearwaters are nocturnal seabirds that rely on olfaction and acoustics to communicate at night. Although previous studies have described the vocal repertoire of some shearwater species, there is a need for more precise experimental data investigating the biological relevance of these acoustic signals in this seabird group. The present paper focuses on the vocal behaviour of the Yelkouan shearwater Puffinus yelkouan, a poorly studied species which produces a single major call composed of two notes, a noisy note and a clear one. A quantitative analysis of the calls allowed to extract the acoustic parameters supporting both sexual and individual signatures. Playback experiments were conducted during the incubation period to test the ability of the Yelkouan shearwater (1) to vocally identify the sex of the emitter, and (2) to discriminate the mate from a non-mate. We showed that birds discriminate the sex of the emitter, calling back almost exclusively to calls of birds of the same sex. Among the few birds replying to calls of the opposite sex, females responded to calls of their partner only, whereas males responded equally to calls of the partner or to calls of a non-partner, suggesting that females are vocally more selective than males.     

Microgeographic Variation and Sharing of the Gargle Vocalization and Its Component Syllables in Black-Capped Chickadee (Aves, Paridae, Poecile atricapillus) Populations

Throughout the year during agonistic encounters, black‐capped chickadees (Poecile atricapillus) emit a vocal signal known as the gargle call. Each bird has a repertoire of structurally differing gargle calls; some are shared with others in the local area. As a basis for understanding the cultural evolution of this social signal, we initiated a study of gargle call repertoires of birds living in a narrow belt of continuous riparian habitat occupied throughout by a resident population of chickadees. During two consecutive winter seasons, we sampled repertoires at three locations over a distance of 8.4 km to quantify micro‐geographical variation. Analyses of vocal sharing and population differentiation were carried out on whole gargle calls and on the individual acoustic units (syllables) from which the whole calls are constructed. We analysed 28 380 calls of 46 subjects in the two seasons of study. Birds averaged 7.6 different calls in their gargle repertoires. Calls were composed of about 10 syllables on average. Fifty‐six different syllables were used to construct the calls of all birds. Each study site had some gargle calls unique to the local birds and some that were shared with one or both of the other two sites. There was significantly greater sharing of both calls and syllables among birds within sample sites than between sample sites. The frequencies of the different kinds of gargles and syllables were significantly correlated across the 2 yr of the study, but the correlation was stronger (r² = 0.93) for syllables than for whole gargle calls (r² = 0.61).     

Vocal matching and intensity of begging calls are associated with a forebrain song circuit in a generalist brood parasite

Vocalizations produced by developing young early in life have simple acoustic features and are thought to be innate. Complex forms of early vocal learning are less likely to evolve in young altricial songbirds because the forebrain vocal‐learning circuit is underdeveloped during the period when early vocalizations are produced. However, selective pressure experienced in early postnatal life may lead to early vocal learning that is likely controlled by a simpler brain circuit. We found the food begging calls produced by fledglings of the brown‐headed cowbird (Molothrus ater), a generalist avian brood parasite, induced the expression of several immediate early genes and early circuit innervation in a forebrain vocal‐motor pathway that is later used for vocal imitation. The forebrain neural activity was correlated with vocal intensity and variability of begging calls that appears to allow cowbirds to vocally match host nestmates. The begging‐induced forebrain circuits we observed in fledgling cowbirds were not detected in nonparasitic passerines, including species that are close relatives to the cowbird. The involvement of forebrain vocal circuits during fledgling begging and its association with vocal learning plasticity may be an adaptation that provides young generalist brood parasites with a flexible signaling strategy to procure food from a wide range of heterospecific host parents. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 615–625, 2016