Whistling in the Dark: an Acoustic Study of Little Spotted Kiwi

<p>Song function and evolution are two central topics of avian bioacoustic research. Discerning why birds sing and why they have such diversity of song can yield rich information on behaviour and speciation, and can provide important tools for conservation. Knowledge of vocal behaviour of a wide range of bird groups is necessary, yet avian bioacoustic studies have been hampered by a bias towards male song birds, with many species and even whole groups relatively unstudied. The New Zealand kiwi (Apterygidae) are vocal and threatened taxa, and calls play an important part in their conservation. Yet kiwi acoustic behaviour is poorly understood, and although the five species differ significantly in their ecology, only one has been subject to detailed acoustic study. This thesis addresses this gap in knowledge of kiwi ecology with the first acoustic study of the little spotted kiwi (LSK). The principal aims are to improve understanding of kiwi calling behaviour, and to provide further acoustic tools for kiwi conservation. On a broader scale, enhanced knowledge of the acoustic ecology of the taxonomically and ecologically distinct kiwi will provide insight into song function and signal evolution in all birds. Sexual call dimorphism in LSK is shown to be unrelated to size differences, and instead has likely functional significance, with male calls more suited for territorial defence. There is striking ‘acoustic cooperation’ between the sexes which constrains the function of duets in LSK. Analysis of complex vocal features, the first in any ratite, reveals that two-voicing is unexpectedly rare in this species, but that non-linear phenomena are common. Their association with territorial calls and high frequencies indicates that these features provide acoustic emphasis to enhance resource defence or convey aggression or fitness information. Non-linear phenomena are very common in nestling LSK calls, in accordance with the hypothesis that they add unpredictability to prevent habituation. LSK have surprisingly low inter-individual call variability, suggesting that this species may not use calls for individual identification. This lack of variability may be a result of the low genetic diversity in this species. A long-term dataset reveals significant fluctuations in calling rates with temporal and environmental factors. These trends indicate that calls serve an important function for reproduction and pair contact, and that calls may reflect foraging activity. They also provide evidence that kiwi are adversely affected by light pollution. A comparison of automated acoustic methods with manual call counts shows that while they have a different biases, autonomous techniques are highly effective for kiwi conservation monitoring. Microphone array methods have great potential for enhancing conservation and behavioural information through spatial monitoring of kiwi, but are demonstrated not to be suitable with currently available equipment.</p>

Whistling in the Dark: an Acoustic Study of Little Spotted Kiwi

<p>Song function and evolution are two central topics of avian bioacoustic research. Discerning why birds sing and why they have such diversity of song can yield rich information on behaviour and speciation, and can provide important tools for conservation. Knowledge of vocal behaviour of a wide range of bird groups is necessary, yet avian bioacoustic studies have been hampered by a bias towards male song birds, with many species and even whole groups relatively unstudied. The New Zealand kiwi (Apterygidae) are vocal and threatened taxa, and calls play an important part in their conservation. Yet kiwi acoustic behaviour is poorly understood, and although the five species differ significantly in their ecology, only one has been subject to detailed acoustic study. This thesis addresses this gap in knowledge of kiwi ecology with the first acoustic study of the little spotted kiwi (LSK). The principal aims are to improve understanding of kiwi calling behaviour, and to provide further acoustic tools for kiwi conservation. On a broader scale, enhanced knowledge of the acoustic ecology of the taxonomically and ecologically distinct kiwi will provide insight into song function and signal evolution in all birds. Sexual call dimorphism in LSK is shown to be unrelated to size differences, and instead has likely functional significance, with male calls more suited for territorial defence. There is striking ‘acoustic cooperation’ between the sexes which constrains the function of duets in LSK. Analysis of complex vocal features, the first in any ratite, reveals that two-voicing is unexpectedly rare in this species, but that non-linear phenomena are common. Their association with territorial calls and high frequencies indicates that these features provide acoustic emphasis to enhance resource defence or convey aggression or fitness information. Non-linear phenomena are very common in nestling LSK calls, in accordance with the hypothesis that they add unpredictability to prevent habituation. LSK have surprisingly low inter-individual call variability, suggesting that this species may not use calls for individual identification. This lack of variability may be a result of the low genetic diversity in this species. A long-term dataset reveals significant fluctuations in calling rates with temporal and environmental factors. These trends indicate that calls serve an important function for reproduction and pair contact, and that calls may reflect foraging activity. They also provide evidence that kiwi are adversely affected by light pollution. A comparison of automated acoustic methods with manual call counts shows that while they have a different biases, autonomous techniques are highly effective for kiwi conservation monitoring. Microphone array methods have great potential for enhancing conservation and behavioural information through spatial monitoring of kiwi, but are demonstrated not to be suitable with currently available equipment.</p>

Vocal modulation in human mating and competition

The human voice is dynamic, and people modulate their voices across different social interactions. This article presents a review of the literature examining natural vocal modulation in social contexts relevant to human mating and intrasexual competition. Altering acoustic parameters during speech, particularly pitch, in response to mating and competitive contexts can influence social perception and indicate certain qualities of the speaker. For instance, a lowered voice pitch is often used to exert dominance, display status and compete with rivals. Changes in voice can also serve as a salient medium for signalling a person's attraction to another, and there is evidence to support the notion that attraction and/or romantic interest can be distinguished through vocal tones alone. Individuals can purposely change their vocal behaviour in attempt to sound more attractive and to facilitate courtship success. Several findings also point to the effectiveness of vocal change as a mechanism for communicating relationship status. As future studies continue to explore vocal modulation in the arena of human mating, we will gain a better understanding of how and why vocal modulation varies across social contexts and its impact on receiver psychology. This article is part of the theme issue ‘Voice modulation: from origin and mechanism to social impact (Part I)’.

Lesser spot-nosed monkeys coordinate alarm call production with associated Campbell’s monkeys

Forest monkeys often form semi-permanent mixed-species associations to increase group-size related anti-predator benefits without corresponding increases in resource competition. In this study, we analysed the alarm call system of lesser spot-nosed monkeys, a primate that spends most of its time in mixed-species groups while occupying the lowest and presumably most dangerous part of the forest canopy. In contrast to other primate species, we found no evidence for predator-specific alarm calls. Instead, males gave one general alarm call type (‘kroo’) to three main dangers (i.e., crowned eagles, leopards and falling trees) and a second call type (‘tcha-kow’) as a coordinated response to calls produced in non-predatory contexts (‘boom’) by associated male Campbell’s monkeys. Production of ‘kroo’ calls was also strongly affected by the alarm calling behaviour of male Campbell’s monkeys, suggesting that male lesser spot-nosed monkeys adjust their alarm call production to another species’ vocal behaviour. We discuss different hypotheses for this unusual phenomenon and propose that high predation pressure can lead to reliance on other species vocal behaviour to minimise predation. Significance statement Predation can lead to the evolution of acoustically distinct, predator-specific alarm calls. However, there are occasional reports of species lacking such abilities, despite diverse predation pressure, suggesting that evolutionary mechanisms are more complex. We conducted field experiments to systematically describe the alarm calling behaviour of lesser spot-nosed monkeys, an arboreal primate living in the lower forest strata where pressure from different predators is high. We found evidence for two acoustically distinct calls but, contrary to other primates in the same habitat, no evidence for predator-specific alarms. Instead, callers produced one alarm call type (‘kroo’) to all predator classes and another call type (‘tcha-kow’) to non-predatory dangers, but only as a response to a specific vocalisation of Campbell’s monkeys (‘boom’). The production of both calls was affected by the calling behaviour of Campbell’s monkeys, suggesting that lesser spot-nosed monkey vocal behaviour is dependent on the antipredator behaviour of other species. Our study advances the theory of interspecies interactions and evolution of alarm calls.

Follow the leader? Orange-fronted conures eavesdrop on conspecific vocal performance and utilise it in social decisions

Animals regularly use social information to make fitness-relevant decisions. Particularly in social interactions, social information can reduce uncertainty about the relative quality of conspecifics, thus optimising decisions on with whom and how to interact. One important resource for individuals living in social environments is the production of information by signalling conspecifics. Recent research has suggested that some species of parrots engage in affiliative contact call matching and that these interactions may be available to conspecific unintended receivers. However, it remains unclear what information third parties may gain from contact call matching and how it can be utilised during flock decisions. Here, using a combined choice and playback experiment, we investigated the flock fusion choices and vocal behaviour of a social parrot species, the orange-fronted conure (Eupsittula canicularis), to a contact call matching interaction between two individuals of different sexes and with different vocal roles. Our results revealed that orange-fronted conures chose to follow vocal leaders more often than vocal followers during fusions. Furthermore, flocks responded with higher call rates and matched the stimulus calls closer when subsequently choosing a vocal leader. Interestingly, orange-fronted conures also showed higher contact call rates and closer matches when choosing males over females. These results suggest that paying attention to conspecific contact call interactions can provide individuals with social information that can be utilised during fission and fusion events, significantly influencing the social dynamics of orange-fronted conures.

Echolocation reverses information flow in a cortical vocalization network

The mammalian frontal and auditory cortices are fundamental structures supporting vocal behaviour, yet the patterns of information exchange between these regions during vocalization remain unknown. Here, we address this issue by means of electrophysiological recordings in the fronto-auditory network of freely-vocalizing Carollia perspicillata bats. We show that oscillations in frontal and auditory cortices predict vocalization type with complementary patterns across structures. Transfer entropy analyses of oscillatory activity revealed directed information exchange in the circuit, predominantly of top-down nature (frontal to auditory). The dynamics of information flow depended on vocalization type and on the timing relative to vocal onset. Remarkably, we observed the emergence of predominant bottom-up information transfer, only when animals produced calls with imminent post-vocal consequences (echolocation signals). These results unveil changes of information flow in a large-scale sensory and association network associated to the behavioural consequences of vocalization in a highly vocal mammalian model.