Contact Calls Research Articles

Behavioural strategies associated with using an ephemeral roosting resource in Spix's disc-winged bat

The limited availability of refuges may represent an important factor promoting the evolution of sociality, particularly in bats. Spix's disc-winged bats ( Thyroptera tricolor ) show highly specialized morphological adaptations that enable individuals to roost inside furled musoid leaves. This roosting ecology presents major challenges, as leaves rapidly unfurl, forcing bats to locate new roosts on a daily basis. Despite the reliance of T. tricolor on such ephemeral roosting resources, bats form stable group associations. This social stability has been attributed to the potential benefits that group members gain from searching for new roosts together versus alone. The purpose of our study was to characterize the behavioural patterns associated with assessing roosts and any accompanying communication strategies of Spix's disc-winged bat. We determined that bats regularly monitor furled leaves within their roosting range, during which they emit a number of distinct social calls. Roost assessment involved close inspection of leaf dimensions and surroundings, and was mostly performed by single individuals. Thyroptera tricolor 's call repertoire during flight indicates that group contact involves a combination of acoustic signals. Our approach in a natural setting provides valuable insight into the role of shelter stability in the evolution of the T. tricolor social system. • Thyroptera tricolor form stable group associations despite the need to constantly switch roosts. • We investigated the behaviour involved in the selection of day roosts. • Bats regularly monitor furled leaves within their roosting range during the night. • We document the presence of multiple contact calls emitted by bats near potential roosts. • Contact calls may enable bats to advertise suitable roost locations.

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.

Vocal behavior of Crested Guineafowl (Guttera edouardi) based on visual and sound playback surveys in the Umhlanga Lagoon Nature Reserve, KwaZulu-Natal province, South Africa

Generally speaking, playbacks were often ineffective to determine the group sizes of birds since mainly males from leks responded. This limitation has not been tested properly for flocking birds such as Crested Guineafowl (Guttera edouardi) with the view to use it as a counting method. The aims of the study reported in this paper were (1) to describe the calls of Crested Guineafowl in a social context; (2) to interpret calls in an evolutionary context; and (3) to demonstrate that playbacks can be used to locate and count Crested Guineafowl in small isolated forests. The vocal behavior of Crested Guineafowl was observed during a survey conducted in the Umhlanga Lagoon Nature Reserve (KwaZulu-Natal, South Africa) from November 2010 to June 2012. Transect line observations and sound playback methods were used. The behavioral context and structure of calls were described. The eight calls described for Crested Guineafowl were produced mainly to unite flock members in the dense understory, where visibility was poor, and to repel intruders. When not disturbed, Crested Guineafowl were quiet and only made soft contact calls. The high rate of call back and the fact that flocks invariably approach the source of the call en masse, shows that field researchers are able to assess the population size of Crested Guineafowl with sound playbacks along a transect. The value of playbacks as a conservation tool is assessed.

Why signal softly? The structure, function and evolutionary significance of low-amplitude signals

Acoustic signalling is a taxonomically widespread form of animal communication consisting of long-range, high-amplitude signals and short-range, low-amplitude signals. Research on acoustic communication has emphasized high-amplitude signals and often overlooked low-amplitude signals, even though they are produced in behavioural contexts that directly influence fitness. Low-amplitude signals are referred to by a variety of names such as soft songs, courtship songs, whispers, close calls, contact calls, grunts and moans, but all of these signals share a reduced amplitude and an active space that is limited to close-proximity receivers. In this review, we establish a general definition for low-amplitude signals and investigate the similarities and differences between low- and high-amplitude signals with respect to their acoustic structure and function. Then, we critically evaluate some proximate and ultimate evolutionary mechanisms that may explain why these signals are produced at low amplitude using examples from a variety of taxa. We conclude by suggesting priorities for future research on low-amplitude signals and highlighting how studying these signals will lead to a more complete understanding of how and why animals communicate acoustically.

Pro-social 50-kHz ultrasonic communication in rats: post-weaning but not post-adolescent social isolation leads to social impairments-phenotypic rescue by re-socialization.

Rats are highly social animals and social play during adolescence has an important role for social development, hence post-weaning social isolation is widely used to study the adverse effects of juvenile social deprivation and to induce behavioral phenotypes relevant to neuropsychiatric disorders, like schizophrenia. Communication is an important component of the rat's social behavior repertoire, with ultrasonic vocalizations (USV) serving as situation-dependent affective signals. High-frequency 50-kHz USV occur in appetitive situations and induce approach behavior, supporting the notion that they serve as social contact calls; however, post-weaning isolation effects on the behavioral changes displayed by the receiver in response to USV have yet to be studied. We therefore investigated the impact of post-weaning isolation on socio-affective information processing as assessed by means of our established 50-kHz USV radial maze playback paradigm. We showed that post-weaning social isolation specifically affected the behavioral response to playback of pro-social 50-kHz but not alarm 22-kHz USV. While group-housed rats showed the expected preference, i.e., approach, toward 50-kHz USV, the response was even stronger in short-term isolated rats (i.e., 1 day), possibly due to a higher level of social motivation. In contrast, no approach was observed in long-term isolated rats (i.e., 4 weeks). Importantly, deficits in approach were reversed by peer-mediated re-socialization and could not be observed after post-adolescent social isolation, indicating a critical period for social development during adolescence. Together, these results highlight the importance of social experience for affiliative behavior, suggesting a critical involvement of play behavior on socio-affective information processing in rats.

Cooperative vocal control in marmoset monkeys via vocal feedback.

Humans adjust speech amplitude as a function of distance from a listener; we do so in a manner that would compensate for such distance. This ability is presumed to be the product of high-level sociocognitive skills. Nonhuman primates are thought to lack such socially related flexibility in vocal production. Using predictions from a simple arousal-based model whereby vocal feedback from a conspecific modulates the drive to produce a vocalization, we tested whether another primate exhibits this type of cooperative vocal control. We conducted a playback experiment with marmoset monkeys and simulated "far-away" and "nearby" conspecifics using contact calls that differed in sound intensity. We found that marmoset monkeys increased the amplitude of their contact calls and produced such calls with shorter response latencies toward more distant conspecifics. The same was not true in response to changing levels of background noise. To account for how simulated conspecific distance can change both the amplitude and timing of vocal responses, we developed a model that incorporates dynamic interactions between the auditory system and limbic "drive" systems. Overall, our data show that, like humans, marmoset monkeys cooperatively control the acoustics of their vocalizations according to changes in listener distance, increasing the likelihood that a conspecific will hear their call. However, we propose that such cooperative vocal control is a system property that does not necessitate any particularly advanced sociocognitive skill. At least in marmosets, this vocal control can be parsimoniously explained by the regulation of arousal states across two interacting individuals via vocal feedback.

Chestnut-crowned babblers show affinity for calls of removed group members: a dual playback without expectancy violation

Cooperative breeding typically evolves within discrete, stable groups of individuals, in which group members derive direct and/or indirect fitness benefits from cooperative behaviour. In such systems, strong selection on group discrimination should emerge. Despite this prediction, relatively few studies have investigated the mechanism of group discrimination in cooperative vertebrates, and the results of many may be confounded by ‘expectancy violation’, since test individuals from which stimuli were derived remained in the group during experimentation. Here, we used a novel experimental protocol that eliminates this confounding effect in a test of group discrimination in cooperatively breeding chestnut-crowned babblers, Pomatostomus ruficeps , using long-distance contact calls. Long-distance contact calls were found to be individually specific, but to lack obvious group level signatures. Using dual playbacks of removed group and nongroup members, we found that these calls allow effective discrimination: groups unanimously approached the speaker broadcasting calls of group members and concomitantly increased their contact call rates. Together, our results suggest that group discrimination emerges from individual recognition. Additionally, the affiliative behaviour of group members towards playbacks of removed members contrasts with the aggressive responses towards nongroup members found in all other studies. One explanation for these differences stems from our elimination of expectancy violation, but further studies are required to verify this.

From where to what: a neuroanatomically based evolutionary model of the emergence of speech in humans.

In the brain of primates, the auditory cortex connects with the frontal lobe via the temporal pole (auditory ventral stream; AVS) and via the inferior parietal lobule (auditory dorsal stream; ADS). The AVS is responsible for sound recognition, and the ADS for sound-localization, voice detection and audio-visual integration. I propose that the primary role of the ADS in monkeys/apes is the perception and response to contact calls. These calls are exchanged between tribe members (e.g., mother-offspring) and are used for monitoring location. Perception of contact calls occurs by the ADS detecting a voice, localizing it, and verifying that the corresponding face is out of sight. The auditory cortex then projects to parieto-frontal visuospatial regions (visual dorsal stream) for searching the caller, and via a series of frontal lobe-brainstem connections, a contact call is produced in return. Because the human ADS processes also speech production and repetition, I further describe a course for the development of speech in humans. I propose that, due to duplication of a parietal region and its frontal projections, and strengthening of direct frontal-brainstem connections, the ADS converted auditory input directly to vocal regions in the frontal lobe, which endowed early Hominans with partial vocal control. This enabled offspring to modify their contact calls with intonations for signaling different distress levels to their mother. Vocal control could then enable question-answer conversations, by offspring emitting a low-level distress call for inquiring about the safety of objects, and mothers responding with high- or low-level distress calls. Gradually, the ADS and the direct frontal-brainstem connections became more robust and vocal control became more volitional. Eventually, individuals were capable of inventing new words and offspring were capable of inquiring about objects in their environment and learning their names via mimicry.

Pharmacology of Ultrasonic Vocalizations in adult Rats: Significance, Call Classification and Neural Substrate.

Pharmacological studies of emotional arousal and initiation of emotional states in rats measured by their ultrasonic vocalizations are reviewed. It is postulated that emission of vocalizations is an inseparable feature of emotional states and it evolved from mother-infant interaction. Positive emotional states are associated with emission of 50 kHz vocalizations that could be induced by rewarding situations and dopaminergic activation of the nucleus accumbens and are mediated by D1, D2, and partially D3 dopamine receptors. Three biologically significant subtypes of 50 kHz vocalizations have been identified, all expressing positive emotional states: (1) flat calls without frequency modulation that serve as contact calls during social interactions; (2) frequencymodulated calls without trills that signal rewarding and significantly motivated situation; and (3) frequency-modulated calls with trills or trills themselves that are emitted in highly emotional situations associated with intensive affective state. Negative emotional states are associated with emission of 22 kHz vocalizations that could be induced by aversive situations, muscarinic cholinergic activation of limbic areas of medial diencephalon and forebrain, and are mediated by M2 muscarinic receptors. Two biologically significant subtypes of 22 kHz vocalizations have been identified, both expressing negative emotional sates: (1) long calls that serve as alarm calls and signal external danger; and (2) short calls that express a state of discomfort without external danger. The positive and negative states with emission of vocalizations are initiated by two ascending reticular activating subsystems: the mesolimbic dopaminergic subsystem as a specific positive arousal system, and the mesolimbic cholinergic subsystem as a specific negative arousal system.

Rupture in long-term vocal recognition of past social partners in bonobos

Bonobos live in dense forest habitats where visual communication is often limited rendering vocal signals important to regulate their social interactions. Moreover their fluid fission-fusion society requires contact over long distances, suggesting that vocal signals of group members are recognised individually. To this end, individual signatures should be reliably encoded in vocal interactions and memorised by recipients over long periods. In this study we investigated individual vocal recognition of group members that had been separated for long periods of time (two to nine years) with varying relationships. In the wild, long-term separation happens regularly, usually in relation to female migration. In captivity, the same process takes place during the transfer of individuals between zoos, mimicking wild migration. We simulated bonobo transfers by broadcasting contact calls of familiar or unfamiliar individuals to our subjects, thus imitating the arrival of new group members. In total, we tested 15 bonobos (> 10 years old) from three European zoos and compared their behavioural responses. We found that bonobos responded differently to familiar voices than to stranger voices, even after prolonged separation. However, the recognition of past partners appears to diminish after being separated for 6-8 years. This interesting result will be discussed regarding to the social needs in bonobos.

The power of oral and nasal calls to discriminate individual mothers and offspring in red deer, Cervus elaphus.

BackgroundIn most species, acoustical cues are crucial for mother-offspring recognition. Studies of a few species of ungulates showed that potential for individual recognition may differ between nasal and oral contact calls.ResultsVocalizations of 28 hinds and 31 calves of farmed Iberian red deer (Cervus elaphus hispanicus) were examined with discriminant function analyses (DFA) to determine whether acoustic structure of their oral and nasal contact calls encodes information about the caller’s identity. Contact calls were elicited by brief separation of individually identified animals by a distance over 10 m or by a bar fence. Both oral and nasal calls of both hinds and calves showed high potential to discriminate individuals. In hinds, individuality was significantly higher in the oral than in the nasal calls, whereas in calves, individuality was equally well expressed in both oral and nasal calls. For calves, the maximum fundamental frequency was higher and the duration was longer in oral calls than in nasal calls. For hinds, the maximum fundamental frequency and the duration were indistinguishable between oral and nasal calls. Compared to the pooled sample of oral and nasal calls, separate oral or nasal call samples provided better classifying accuracy to individual in either hinds or calves. Nevertheless, in both hinds and calves, even in the pooled sample of oral and nasal calls, the degree of individual identity was 2–3 times greater than expected by chance. For hinds that provided calls in both years, cross-validation of calls collected in 2012 with discriminant functions created with calls from 2011 showed a strong decrease of classifying accuracy to individual.ConclusionsThese results suggest different potentials of nasal and oral calls to allow the discrimination of individuals among hinds, but not among red deer calves. The high potential of individual recognition even with the pooled sample of oral and nasal calls allows mother and young to remember only one set of acoustic variables for mutual vocal recognition. Poor between-year stability of individual characteristics of hind oral and nasal calls would require updating keys to individual recognition each calving season.Electronic supplementary materialThe online version of this article (doi:10.1186/s12983-014-0094-5) contains supplementary material, which is available to authorized users.

Differences in short-term vocal learning in parrots, a comparative study

Parrots are renowned for their vocal learning abilities. Yet only few parrot species have been investigated and empirically proven to possess vocal learning abilities. The aim of this study was to investigate if short-term vocal learning may be a widespread phenomenon among Psittaciformes. Through an interactive experiment we compare the ability of four parrot species, the peach-fronted conure (Aratinga aurea), the cockatiel (Nymphicus hollandicus), the peach-faced lovebird (Agapornis roseicollis) and the budgerigar (Melopsittacus undulatus), to vocally match playback of contact calls. All four species made an overall change to their contact call in response to the playback, and they also varied the degree of similarity with the playback call throughout the playback experiment. The peach-fronted conure showed the biggest overall changes to their contact calls by vocally matching the playback call and the budgerigar showed the least change. The cockatiel and the peach-faced lovebird showed intermediary levels of change making their calls overall less similar to the playback call. The peach-fronted conure responded with highest similarity to familiar individuals and the cockatiel responded with an overall higher similarity to female playback stimuli. Cockatiel males and budgerigar males responded with a higher call rate to playback than female conspecifics. Peach-faced lovebirds responded fastest to unfamiliar males. Based on the results we conclude that short-term vocal learning is a widespread phenomenon among parrots. The way short-term vocal learning is used however, differs between species suggesting that short-term vocal learning have different functions in different species.

Repeatability in the contact calling system of Spix's disc-winged bat (Thyroptera tricolor).

Spix's disc-winged bat (Thyroptera tricolor) forms cohesive groups despite using an extremely ephemeral roost, partly due to the use of two acoustic signals that help individuals locate roost sites and group members. While the calls that aid in group cohesion are commonly used, some bats rarely or never produce them. Here, we examine whether the differences observed in the contact calling behaviour of T. tricolor are repeatable; that is, whether individual differences are consistent. We recorded contact calls of individuals in the field and rates and patterns of vocalization. To determine whether measured variables were consistent within individuals, we estimated repeatability (R), which compares within-individual to among-individual variance in behavioural traits. Our results show that repeatability for call variables was moderate but significant, and that repeatability was highest for the average number of calls produced (R=0.46–0.49). Our results demonstrate important individual differences in the contact calling behaviour of T. tricolor; we discuss how these could be the result of mechanisms such as frequency-dependent selection that favour groups composed of individuals with diverse vocal strategies. Future work should address whether changes in social environment, specifically group membership and social status, affect vocal behaviour.

The use of call imitation to establish territory occupancy by Leadbeater's possum (Gymnobelideus leadbeateri)

Leadbeater’s possum (Gymnobelideus leadbeateri) is a cryptic, endangered species that is notoriously difficult to detect using conventional mammal survey methods. However, the imitation of the species’ social contact and/or alarm calls has previously been found to attract resident animals. Call imitation was employed as a secondary survey method to confirm ongoing site occupancy by Leadbeater’s possum at Yellingbo Nature Conservation Reserve. All call imitation reported here was conducted at sites currently or previously known to be occupied by particular family groups. The results indicate that the method has considerable promise as a tool to facilitate broad-scale surveys targeting this species. However, ‘false negatives’ did occur during the surveys at Yellingbo, highlighting that additional testing is required to adequately characterise the species’ response patterns, in particular variation in the response rate in occupied territories and the distance over which animals will respond. A detailed understanding of these factors is essential to permit reliable interpretation of survey findings.

Acoustic Communication in Rats: Effects of Social Experiences on Ultrasonic Vocalizations as Socio-affective Signals.

Ultrasonic vocalizations (USV) serve important communicative functions as socio-affective signals in rats. In aversive situations, such as inter-male aggression and predator exposure, 22-kHz USV are emitted. They likely function as appeasement signals during fighting and/or as alarm calls to warn conspecifics. In appetitive situations, 50-kHz USV are uttered, most notably during social interactions, such as rough-and-tumble play and mating. It is believed that they fulfill an affiliative function as social contact calls. Social experiences or their lack, such as social isolation, can have profound impact on the emission of 22- and 50-kHz USV by the sender in later life, albeit direction and strength of observed effects vary, with time point of occurrence and duration being critical determinants. Little, however, is known about how social experiences affect the behavioral responses evoked by 22- and 50-kHz USV in the recipient. By means of our 50-kHz USV radial maze playback paradigm, we recently showed that the behavioral response elicited in the recipient is affected by post-weaning social isolation. Rats exposed to four weeks of isolation during the rough-and-tumble play period did not display social approach behavior toward 50-kHz USV but some signs of social avoidance. We further found that physical environmental enrichment providing minimal opportunities for social interactions has similar detrimental effects. Together, this indicates that social experiences can affect socio-affective communication in rodents, both at the level of sender and recipient. Deficits seen following post-weaning social isolation or physical environmental enrichment might be useful to model aspects of neurodevelopmental disorders characterized by social and communication deficits, such as autism and schizophrenia.

Vocalisations of the bigeye Pempheris adspersa: characteristics, source level and active space.

Fish sounds are an important biological component of the underwater soundscape. Understanding species-specific sounds and their associated behaviour is critical for determining how animals use the biological component of the soundscape. Using both field and laboratory experiments, we describe the sound production of a nocturnal planktivore, Pempheris adspersa (New Zealand bigeye), and provide calculations for the potential effective distance of the sound for intraspecific communication. Bigeye vocalisations recorded in the field were confirmed as such by tank recordings. They can be described as popping sounds, with individual pops of short duration (7.9±0.3 ms) and a peak frequency of 405±12 Hz. Sound production varied during a 24 h period, with peak vocalisation activity occurring during the night, when the fish are most active. The source level of the bigeye vocalisation was 115.8±0.2 dB re. 1 µPa at 1 m, which is relatively quiet compared with other soniferous fish. Effective calling range, or active space, depended on both season and lunar phase, with a maximum calling distance of 31.6 m and a minimum of 0.6 m. The bigeyes' nocturnal behaviour, characteristics of their vocalisation, source level and the spatial scale of its active space reported in the current study demonstrate the potential for fish vocalisations to function effectively as contact calls for maintaining school cohesion in darkness.

Conspicuous calling near cryptic nests: a review of hypotheses and a field study on white‐browed scrubwrens

Predation is an important source of nest mortality in many bird species and calling near the nest can increase this risk, yet adults of many species regularly vocalize near their nests. Some of these calls serve clearly adaptive functions, such as alarm or provisioning calls. However, many species also give conspicuous ‘contact’ calls near the nest, which is puzzling because the function of these calls is unclear, and they might attract predators. Most studies of parental vocalizations near nests have focused on specific vocalizations and single hypotheses, yet there is a diversity of vocalization types and potential functions. We review the literature on the diversity and possible function of parental vocalizations near the nest, and then investigate the puzzle of conspicuous contact calling near nests by white‐browed scrubwrens Sericornis frontalis. In scrubwrens, ‘chip‐zz’ contact calls were almost always used when adults approached nests, and when they approached one another or changed location. Call composition also changed: the proportion of ‘chip’ elements increased as callers approached the nest or other adults. Neither adult sex nor nestling age affected calling. Thus, chip‐zz calls appear to be used as ongoing signals to other group members of the caller's activity and location, particularly relative to the nest. Nestlings appeared to use the calls as cues of adult arrival, and increased calling as adults approached nests. Further, adults called less after a predator was on the territory, suggesting that parents may be able to reduce the risk of chip‐zz calls betraying nest location, or possibly use the absence of calling as a signal of danger. This study thus demonstrates that calling near nests could inform both adults and nestlings about the caller's behaviour, and could serve multiple functions. Future studies will need to experimentally test these functions, as well as the other hypotheses reviewed here.

Within-group vocal differentiation of individuals in the cooperatively breeding apostlebird

The ability of animals to discriminate between individuals or groups of individuals (e.g., kin or nonkin) is an important component of many hypotheses proposed to explain the evolution of cooperation and benefits of group living. Previous studies in mammalian systems have demonstrated the use of vocal cues in individual recognition and discrimination. However, there are few such studies in birds. Previous avian studies have largely examined discrimination between different categories of individuals (e.g., mate vs. nonmate, offspring vs. non-offspring) while discrimination between individuals of the same category remain largely unexplored. Previous work has demonstrated that the contact calls of free-living apostlebirds (Struthidea cinerea) are individually distinct. Here, we demonstrate that apostlebirds can differentiate between the calls of other individuals of the same social group using vocal cues alone. These findings are biologically relevant as apostlebirds live in complex fission–fusion societies where social groups vary in size, sex ratio, number of breeders, and composition of related and unrelated members.

Acoustic analysis of cattle (Bos taurus) mother–offspring contact calls from a source–filter theory perspective

Cattle vocalisations have been proposed as potential indicators of animal welfare. However, very few studies have investigated the acoustic structure and information encoded in these vocalisations using advanced analysis techniques. Vocalisations play key roles in a wide range of communication contexts; e.g. for individual recognition and to help coordinate social behaviours. Two factors have greatly assisted our progress in developing an understanding of animal vocal communication. Firstly, more rigorous call analysis methods allow us to describe the variation in the vocal parameters in unprecedented detail. Secondly, the adoption of the “source–filter theory” of call production links the acoustic structure of vocalisations to the morphology and physiology of calling animals. Using these approaches, it is possible to quantify the potential for each acoustic component to carry information. In this study, we examined naturally occurring contact calls produced by crossbred beef cows and their calves under free-ranging conditions. Our main aims were to identify vocal parameters, which can be used to characterise cow and calf contact calls, and to describe variation in these parameters under relatively undisturbed conditions. Additionally, we aimed to provide information for future studies on potential acoustic indicators of animal welfare in cattle. We identified two different types of cow contact calls associated with different behavioural contexts, and with differing acoustic structures. Low frequency calls (LFCs) were produced by cows when they were in close proximity to their calves, in the first three or four weeks postpartum, and they were made with the mouth closed or only partially open (fundamental frequency (F0)=81.17±0.98Hz). By contrast, high frequency calls (HFCs) were produced by cows when they were separated from their calves (e.g. not in visual contact) and preceded nursing (F0=152.8±3.10Hz). Calf calls were produced when separated from their mothers and preceded suckling (F0=142.8±1.80Hz). A detailed analysis of cow LFCs and HFCs, and of calf calls, showed that all three types of calls are individually distinctive. We also show that calf calls encode age, but not sex. Although it has previously been suggested that cattle contact calls are individually distinctive, to our knowledge, our study is the first to use the most rigorous, modern methods to analyse their calls. This study represents an important advance in our knowledge cattle contact vocalisations, which is essential for future work on cattle communication and welfare.

Silvereyes decrease acoustic frequency but increase efficacy of alarm calls in urban noise

Many passerines adjust song attributes to avoid potential masking by anthropogenic noise. The costs of masking should be particularly high for vocalizations important for survival (e.g. alarm calls), but few studies have investigated how such calls are affected. We compared urban and rural silvereye, Zosterops lateralis, alarm calls across southeastern Australia, and found that urban calls had lower average, peak and maximum frequencies than rural calls. The average, peak and maximum frequency of alarm calls also decreased linearly with increasing background noise. The direction of this frequency shift runs contrary to expectations and previous findings of higher-pitched avian vocal signals in urban habitats, including higher-pitched song and contact calls in urban silvereyes. However, assuming no change in call amplitude, acoustic modelling indicates that the observed frequency shift would lead to a 20% increase in the predicted active space of alarm calls (i.e. the distance over which the calls can be detected by a conspecific bird) in urban noise, and therefore may be potentially adaptive. Our findings highlight the importance of considering behavioural and ecological contexts in urban acoustic-adaptation studies.