Vocal individuality,but not stability,in wild palm cockatoos (Probosciger aterrimus)

The ability to identify individuals within a population is often essential for a detailed understanding of the ecology and conservation of a species. However, some species, including large parrots, are notoriously difficult to catch and mark for individual identification. Palm cockatoos (Probosciger aterrimus) are a large, poorly understood species of parrot which are likely in severe decline within the eastern part – and possibly the western part – of their range on Cape York Peninsula, Australia. Here, we investigated whether three different palm cockatoo call types are sufficiently individually distinctive to function as a non-invasive “marker” for identifying individuals over time. Using Discriminant Function Analysis, overall identification accuracy among 12 putative individuals for all call types was 81% (i.e. 148 out of 183 calls were assigned to the correct individual) on the basis of multiple temporal, energy (amplitude) and frequency measurements on the spectrogram. For three different call types, individual identification accuracy among males and females ranged from 69 to 95%. However, based on a limited sample sizes of five putative individuals between years, our data suggest that individual call structure, as quantified by call parameters, was not stable between years. We discuss the applicability of these results for future studies of palm cockatoos and other parrot species.     

VOCAL REPERTOIRE OF WILD BREEDING ORANGE-WINGED PARROTS AMAZONA AMAZONICA IN AMAZONIA

ABSTRACT

The vocal repertoire of Amazona amazonica during its breeding season has been recorded from wild individuals in Santa Bárbara do Pará, Pará State, Brazil. At individual nests, we continuously recorded vocalizations and behaviour for four hours in the early morning and three hours in the late afternoon, three times a week throughout the breeding season. We identified nine vocalizations that we classified in three behavioural categories: (1) Flight call—emitted when parrots arrive in the nest area; (2) Perched contact calls—two different vocalizations, one of them related to feeding, were emitted when the pair was perched in the nest area and interacted socially between themselves or with other individuals; (3) Aggressive calls—emitted when birds were in a dangerous situation, i.e. alarm (three types of calls), agonistic contact and distress calls (two types of call). The Orange-winged Parrot is a highly social species and the complexity of its social interactions is reflected in the diversity of its vocal repertoire.     

Context-related vocalizations in African grey parrots (Psittacus erithacus)

A few animal species are capable of vocal learning. Parrots are well known for their vocal imitation abilities. In this study, we investigated whether African grey parrots (Psittacus erithacus) emit specific vocalizations in specific contexts. We first described the vocal repertoire and its ontogenesis of four captive grey parrots. After a comparison with vocalizations emitted by wild and other captive African grey parrots, we observed that only three call categories were shared by all grey parrots populations, suggesting that isolated populations of parrots develop population-specific calls. Then, we artificially provoked ten different contexts and recorded vocalizations of four captive grey parrots in these situations. Parrots predominantly emitted call categories in some contexts: distress, protestation, alarm, asking (i.e. emitted when a bird wanted something from an experimenter) and contact calls. These results suggest that some calls are learned and can be used in specific contexts.     

Vertical transmission of learned signatures in a wild parrot

Learned birdsong is a widely used animal model for understanding the acquisition of human speech. Male songbirds often learn songs from adult males during sensitive periods early in life, and sing to attract mates and defend territories. In presumably all of the 350+ parrot species, individuals of both sexes commonly learn vocal signals throughout life to satisfy a wide variety of social functions. Despite intriguing parallels with humans, there have been no experimental studies demonstrating learned vocal production in wild parrots. We studied contact call learning in video-rigged nests of a well-known marked population of green-rumped parrotlets (Forpus passerinus) in Venezuela. Both sexes of naive nestlings developed individually unique contact calls in the nest, and we demonstrate experimentally that signature attributes are learned from both primary care-givers. This represents the first experimental evidence for the mechanisms underlying the transmission of a socially acquired trait in a wild parrot population.     

Male vocal imitation produces call convergence during pair bonding in budgerigars, Melopsittacus undulatus

The budgerigar, a small species of parrot, can learn new vocalizations throughout life and is therefore widely used as a model system for studying various aspects of vocal learning. It is not known, however, why parrots imitate sounds. To test the hypothesis that vocal imitation in budgerigars is related to pair bonding, we recorded approximately 100 contact calls from each of nine male and nine female adult budgerigars that were unfamiliar with one another and then placed them into pairs. We sampled their contact call repertoire weekly and conducted twice-weekly behavioural observation sessions. We compared contact calls by sonagram cross-correlation and classified them by means of a hierarchical clustering algorithm. This analysis showed that all pairs developed a shared call within an average of 2.1 weeks. Further analysis revealed that eight of the nine male budgerigars imitated the contact calls of their assigned mates, while none of the females imitated the calls of their males. We conclude that contact call imitation in adult budgerigars probably contributes to pair bond formation and maintenance. Prior studies on budgerigars were limited by the lack of a behavioural paradigm to elicit vocal imitation reliably. Our study remedies this and thereby serves as a foundation for future studies on vocal learning in adult animals. Copyright 2000 The Association for the Study of Animal Behaviour.     

Is there variation in the response to contact call playbacks across the hybrid zone of the parrot Platycercus elegans?

Learned vocal signals could be important in the formation of prezygotic isolation between two hybridising taxa. This study examined whether vocal variation in the parrot Platycercus elegans facilitates the separation of individuals from two subspecies, P. e. elegans (CR) and P. e. flaveolus (YR). CR and YR have very different plumage coloration, respectively deep crimson and pale yellow, but hybridise where they meet creating an intermediate population (WS). In a factorial design playback experiment, we conducted 108 playback trials on three focal populations (YR, WS, CR), in and around this area of hybridisation, to test if they respond differently to contact calls from their own or another population. We also analysed whether differences in acoustic variables of the stimulus calls predicted the response to the call. We did not find any indication that individuals from the three focal populations responded differently to calls sampled from their own or another subspecies. We did find an effect of two of the five acoustic variables that we used to describe and classify contact calls from the three source populations. Specifically, duration of the stimulus call positively affected the response from individuals from WS and negatively the response from CR, and CR responded more to stimulus calls with a lower peak frequency. Overall, we found no indication that acoustic variation in contact calls on a subspecies level is involved in maintaining plumage colour differences between P. e. elegans and P. e. flaveolus subspecies.     

Dialect change in resident killer whales: implications for vocal learning and cultural transmission

Variation in vocal signals among populations and social groups of animals provides opportunities for the study of the mechanisms of behavioural change and their importance in generating and maintaining behavioural variation. We analysed two call types made by two matrilineal social groups of resident killer whales, Orcinus orca, over 12-13 years. We used a neural network-based index of acoustic similarity to identify mechanisms of call differentiation. A test for structural modification of the calls detected significant changes in one call type in both groups, but not in the other. For the modified call type, the rate of divergence between the two groups was significantly lower than the rate of modification within either group showing that calls were modified in a similar fashion in the two groups. An analysis of structural parameters detected no strong directionality in the change. The pattern of call modification could have been caused by maturational changes to the calls or, if killer whale dialects are learned behavioural traits, cultural drift in the structure of the calls together with horizontal transmission of modifications between the two groups. Such vocal matching between members of different matrilines would suggest that vocal learning is not limited to vertical transmission from mother to offspring, which has important implications for models of gene-culture coevolution. Copyright 2000 The Association for the Study of Animal Behaviour.     

Does vocal learning accelerate acoustic diversification? Evolution of contact calls in Neotropical parrots

Learning has been traditionally thought to accelerate the evolutionary change of behavioural traits. We evaluated the evolutionary rate of learned vocalizations and the interplay of morphology and ecology in the evolution of these signals. We examined contact calls of 51 species of Neotropical parrots from the tribe Arini. Parrots are ideal subjects due to their wide range of body sizes and habitats, and their open‐ended vocal learning that allows them to modify their calls throughout life. We estimated the evolutionary rate of acoustic parameters of parrot contact calls and compared them to those of morphological traits and habitat. We also evaluated the effect of body mass, bill length, vegetation density and species interactions on acoustic parameters of contact calls while controlling for phylogeny. Evolutionary rates of acoustic parameters did not differ from those of our predictor variables except for spectral entropy, which had a significantly slower rate of evolution. We found support for correlated evolution of call duration, and fundamental and peak frequencies with body mass, and of fundamental frequency with bill length. The degree of sympatry between species did not have a significant effect on acoustic parameters. Our results suggest that parrot contact calls, which are learned acoustic signals, show evolutionary rates similar to those of morphological traits. This is the first study to our knowledge to provide evidence that change through cultural evolution does not necessarily accelerate the evolutionary rate of traits acquired through life‐long vocal learning.     

A comparison of individual distinctiveness in three vocalizations of the dwarf mongoose (Helogale parvula)

Individual specificity can be found in the vocalizations of many avian and mammalian species. However, it is often difficult to determine whether these vocal cues to identity rise from “unselected” individual differences in vocal morphology or whether they have been accentuated by selection for the purposes of advertising caller identity. By comparing the level of acoustic individuality of different vocalizations within the repertoire of a single species, it is possible to ascertain whether selection for individual recognition has modified the vocal cues to identity in particular contexts. We used discriminant function analyses to determine the level of accuracy with which calls could be classified to the correct individual caller, for three dwarf mongoose (Helogale parvula) vocalizations: contact, snake, and isolation calls. These calls were similar in acoustic structure but divergent in context and function. We found that all three call types showed individual specificity but levels varied with call type (increasing from snake to contact to isolation call). The individual distinctiveness of each call type appeared to be directly related to the degree of benefit that signalers were likely to accrue from advertising their identity within that call context. We conclude that dwarf mongoose signalers have undergone selection to facilitate vocal individual recognition, particularly in relation to the species’ isolation call.     

Responses to Playback of Local vs. Distant Contact Calls in the Orange-Fronted Conure, Aratinga canicularis

We conducted interactive playback experiments on foraging flocks of orange‐fronted conures, Aratinga canicularis, using loud contact calls that had been recorded at sites ranging from 0 to 30 km from the playback site. Responses were scored on the basis of the proximity of approach to the speaker, the number of different vocalizations produced by the responding flock, and the duration of respondent vocal interactions with the playbacks. Overall response strength decreased significantly as distance between playback and recording sites was increased up to 9 km, and remained at a steady low level for greater distances. As 9 km is the upper limit of conure home ranges measured in this study site, this nonlinear effect of response with distance suggests that response strength is partly determined by familiarity with calls of local birds. An additional and independent amount of the variation in response strength was explained by the structural similarity between respondent and stimulus calls. This correlation could be caused by a preference to interact with known stimulus birds whose calls have converged during prior associations. However, our data suggest that responding birds subtly changed their call structure during longer trials to more closely match the stimulus call. If subsequently verified as a common phenomenon, this finding could provide an important explanation for the remarkable imitative abilities of parrots.     

Dialects in pygmy marmosets? Population variation in call structure

Population variation in primate vocal structure has been rarely observed. Here, we report significant population differences in the structure of two vocalizations in wild pygmy marmosets (Trills and J calls). We studied 14 groups of pygmy marmosets Callithrix (Cebuella) pygmaea pygmaea from five populations in northeastern Ecuador. We analyzed the acoustic structure of Trills and J calls recorded from two adult animals in each group through focal samples. Although individuals and groups within a population differed in call structure, we found consistent structural differences at a population level for Trills and J calls. Pair‐wise comparisons for the two call types point to San Pablo and Amazoonico as the populations that differed the most, whereas Hormiga and Zancudococha showed the least differences. Discriminant function analysis indicates that calls from each population could be classified accurately at rates significantly above chance. Habitat acoustics, social factors and genetic drift may explain interpopulation vocal differences. This is the first evidence of within‐subspecies vocal differences, or dialects, in wild populations of a neotropical primate species. Am. J. Primatol. 71:333–342, 2009. © 2009 Wiley‐Liss, Inc.     

Behavioural response evoked by conspecific distress calls in two neotropical treefrogs

Anurans emit distress calls when attacked by predators as a defensive mechanism. As distress calls may trigger antipredator behaviour even in individuals that are not under attack, we tested whether this defensive behaviour induced behavioural changes in neighbouring conspecifics. We compared the behavioural responses of two species of Neotropical hylid frogs (genus Boana) to conspecific distress calls and white noise. Individuals of both species interrupted their vocal activity and decreased call rate after hearing the distress call. Natural variation on signal intensity calibrated among the nearest neighbours did not influence the response and we did not observe negative phonotaxis after any acoustic stimulus. Despite the fact that many predators are acoustically oriented, we could not determine if such response (reduced call rate) was induced by risk assessment or by the masking effect on advertisement calls. Boana faber responded similarly to white noise and distress calls, while B. bischoffi responded more intensely to distress calls. Duration of silence after playbacks in B. faber was longer than B. bischoffi. We suggest that, if the signals are interpreted as a risk cue by neighbouring conspecifics, each species may be preyed upon by different predators, as they may have led to distinct defensive strategies and different responses to distress calls. If risk assessment information is included in distress calls, it triggers behavioural responses only in the nearest neighbours, as we did not observe responses on the vocal activity of the interspecific chorus. Our results add relevant data about acoustic communication and interpretations by anurans, highlighting the importance of considering cues within common and widespread signals.     

Repeated call sequences and behavioural context in long-finned pilot whales off Cape Breton,Nova Scotia,Canada

Repeated calls are part of the vocal repertoire of a diverse array of species, often presented in sequences that take time and effort on the part of the signal producer. Rhythmic repeated call sequences make up a significant portion of long-finned pilot whale (Globicephala melas) vocal production, yet the function of these sequences has not been investigated until now. In this study, we explored the relationship between behavioural context and the presence of these vocal sequences using recordings of a population of pilot whales found off Cape Breton, Nova Scotia, Canada. We used a binomial logit-link generalized linear model to look for possible predictors of the presence of repeated call sequences. They were more common in recordings of socializing whales than in those of whales in other behavioural states, and least common in resting whales. These vocal repetitions were also more common with larger group size. These results suggest that sequences function in maintaining contact and cohesion within this social species, possibly also serving in individual or group identification. The context of repeated call sequences indicate that they are not primarily mother–calf interactions, as they are heard just as commonly from groups without young. Future studies of pilot whale repeated call sequences should include individual-level behaviour and detailed acoustic calling context.     

‘Virtual Parrots’ Confirm Mating Preferences of Female Budgerigars

Parrots comprise one of the several taxa in which life‐long learning of new vocal signals used in intraspecific communication is known to occur routinely. The functions and evolutionary bases of this ability are largely unknown. In the budgerigar (Melopsittacus undulatus), males typically imitate their partner’s contact call type during pair formation. However, a female’s initial choice among unfamiliar males is not based on their production of her call type, because birds without prior social contact rarely produce the same call type. Here, we demonstrate that female budgerigars prefer unfamiliar males with calls that are similar to their own, as measured by spectrogram cross‐correlation, but which are not imitations. This was shown by training females via operant conditioning to control access to movies of courting males and by systematically varying the audio tracks of these movies. Females learned this task easily and interacted with virtual males as if they were real. This methodology will be useful for exploring functions and mechanisms of social communication, because it eliminates the confounding impact of short‐term changes in a stimulus individual’s behavior on a test individual’s response. Our results suggest that the neuroplastic vocal abilities of budgerigars, and perhaps other parrots, have been shaped by sexual selection.     

Vocal repertoire of cooperatively breeding Smooth‐billed Anis

Calls are functionally diverse signals that mediate behavior in a wide variety of contexts in both passerines and non‐passerines. However, the call‐based acoustic communication systems of non‐passerines have received less attention from investigators than those of passerines. We examined the vocal repertoire of Smooth‐billed Anis (Crotophaga ani), cooperatively breeding cuckoos that live in groups with multiple breeding pairs. We recorded calls from 22 groups over two breeding seasons at the Cabo Rojo National Wildlife Refuge in Puerto Rico. We identified 11 call types and one group vocalization, and used an automated sound measurement program to quantify their acoustic features. Discriminant function analysis (DFA) correctly classified 74.2% of calls based on these features. The vocal repertoire of Smooth‐billed Anis is larger than that reported for the three other species in the subfamily Crotophaginae. Smooth‐billed Anis have at least two alarm calls, two nest‐specific calls, and one nest defense call. We also identified one possible signal of aggressive intent, one possible appeasement signal, and two calls that may communicate identity. The relatively large vocal repertoire of Smooth‐billed Anis and association of distinct call types with different functions and contexts supports the main prediction of the social complexity hypothesis, i.e., species with more complex social systems will have more complex communication systems.     

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).     

Divergence of Acoustic Signals in a Widely Distributed Frog: Relevance of Inter-Male Interactions

Divergence of acoustic signals in a geographic scale results from diverse evolutionary forces acting in parallel and affecting directly inter-male vocal interactions among disjunct populations. Pleurodema thaul is a frog having an extensive latitudinal distribution in Chile along which males'' advertisement calls exhibit an important variation. Using the playback paradigm we studied the evoked vocal responses of males of three populations of P. thaul in Chile, from northern, central and southern distribution. In each population, males were stimulated with standard synthetic calls having the acoustic structure of local and foreign populations. Males of both northern and central populations displayed strong vocal responses when were confronted with the synthetic call of their own populations, giving weaker responses to the call of the southern population. The southern population gave stronger responses to calls of the northern population than to the local call. Furthermore, males in all populations were stimulated with synthetic calls for which the dominant frequency, pulse rate and modulation depth were varied parametrically. Individuals from the northern and central populations gave lower responses to a synthetic call devoid of amplitude modulation relative to stimuli containing modulation depths between 30–100%, whereas the southern population responded similarly to all stimuli in this series. Geographic variation in the evoked vocal responses of males of P. thaul underlines the importance of inter-male interactions in driving the divergence of the acoustic traits and contributes evidence for a role of intra-sexual selection in the evolution of the sound communication system of this anuran.     

VOCAL BEHAVIOUR AND CALL DEVELOPMENT IN THE BULLFINCH (PYRRHULA PYRRHULA)

ABSTRACT

A sonagraphic analysis of the vocalizations of bullfinches Pyrrhula pyrrhula is presented and their behavioural contexts and functions noted. The vocal repertoire of the bullfinch is compared to that of other finches with particular attention to repertoire size and sexual specificity; the repertoire of 14–17 vocal categories is comparatively greater than that of most carduelines and the majority of vocalizations were given by both sexes. The development of nestling, fledgling and some adult calls is described. Early vocal ontogeny in the bullfinch was similar to that previously described for the chaffinch. The earliest recorded calls of nestling bullfinches showed a single fundamental. The independent use of two sound sources became apparent on the second day after hatching and the major elements of the three best studied call types were all derived from the lower fundamental of the nestling begging call.