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Territorial contests often occur in the presence of conspecifics not directly involved in the interaction. Actors may alter their behaviour in the presence of this audience, an ‘audience effect’, and audiences themselves may alter their... more
Territorial contests often occur in the presence of conspecifics not directly involved in the interaction. Actors may alter their behaviour in the presence of this audience, an ‘audience effect’, and audiences themselves may alter their behaviour as a result of observing an interaction, a ‘bystander effect’. Previous work has documented these effects by looking at each in isolation, but to our knowledge, none has investigated their interaction; something that is more likely to represent a realistic scenario for species where individuals aggregate spatially. We therefore have a somewhat limited understanding of the extent and direction of these potentially complex indirect social effects on behaviour. Here we examined how audience and bystander effects work in tandem to modify resident male aggressive behaviour towards intruders in European fiddler crabs, Afruca tangeri. We found that male crabs with an audience showed greater aggressive behaviour towards an intruder compared to males without an audience, but only if they had acted as a bystander to an aggressive signalling interaction prior to the intrusion. Indeed, bystanding during aggressive interactions elevated aggressive responses to intruders maximally if there was an audience present. Our results suggest that bystanding had a priming effect on territory-holding males, potentially by providing information on the immediate level of competition in the local neighbourhood, and that same-sex audiences only matter if males have been primed. This study highlights the fundamental importance of considering broader interaction networks in studying real-world dyadic interactions and of including non-vertebrate taxonomic groups in these studies
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Background The European population of hedgehogs (Erinaceus europaeus) is declining. It is therefore essential to optimise conservation initiatives such as the rehabilitation of sick, injured and orphaned hedgehogs. Wild animals placed in... more
Background The European population of hedgehogs (Erinaceus europaeus) is declining. It is therefore essential to optimise conservation initiatives such as the rehabilitation of sick, injured and orphaned hedgehogs. Wild animals placed in captivity may be prone to chronic stress, potentially causing negative health effects. Therefore, the effects of these rehabilitation efforts should consequently be evaluated. Furthermore, hand-raising orphaned hedgehogs is a laborious and costly task, and it is therefore relevant to document whether they have equal post release survival rates compared to their wild conspecifics. The objectives of this research were therefore to conduct an exploratory study of glucocorticoid levels in hedgehogs from different backgrounds and compare the post release survival of translocated, rehabilitated and wild, juvenile hedgehogs as well as the possible effect on survival of differences in shy or bold behaviour (personality) exhibited by individuals. Results We ...
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Low-frequency ambient noise is known to cause shifts in the song frequency of different species of songbirds, such as the Great Tit (Parus major). The present study was conducted to test the generality of these findings by measuring the... more
Low-frequency ambient noise is known to cause shifts in the song frequency of different species of songbirds, such as the Great Tit (Parus major). The present study was conducted to test the generality of these findings by measuring the distribution of energy across the spectrum of songs of the Great Tit. The studied individuals were either exposed to low-frequency ambient traffic noise in an urban environment (Copenhagen, Denmark) or not exposed to such an environment (the Strødam Reserve north of Copenhagen). A trend throughout all frequency-energy quartiles illustrated that the species sang at an elevated frequency in urban environments compared to rural ones, and that both the upperand lower-frequency-energy quartiles were signifcantly higher in the former.
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Most territorial songbirds live in communication networks where eavesdropping on vocal interactions may constitute an important option for gathering information regarding the relative dominance, condition and quality of individuals being... more
Most territorial songbirds live in communication networks where eavesdropping on vocal interactions may constitute an important option for gathering information regarding the relative dominance, condition and quality of individuals being eavesdropped upon. The relatively low costs and risks of eavesdropping, together with the obvious advantages of gaining such comparative information about other individuals, predict eavesdropping to be a widespread phenomenon even though it is not necessarily advantageous for the participants to be eavesdropped upon. Special eavesdropper strategies that facilitate eavesdropping (how best to eavesdrop) may therefore have evolved together with strategies for interacting that either co-facilitate (public signaling) or counter eavesdropping directly (private signaling) or indirectly by preventing any subsequent negative consequences of being eavesdropped upon (anonymity). This paper reviews the predictions for the strategies and also gives examples supp...
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The ability to imitate complex sounds is rare, and among birds has been found only in parrots, songbirds, and hummingbirds. Parrots exhibit the most advanced vocal mimicry among non-human animals. A few studies have noted differences in... more
The ability to imitate complex sounds is rare, and among birds has been found only in parrots, songbirds, and hummingbirds. Parrots exhibit the most advanced vocal mimicry among non-human animals. A few studies have noted differences in connectivity, brain position and shape in the vocal learning systems of parrots relative to songbirds and hummingbirds. However, only one parrot species, the budgerigar, has been examined and no differences in the presence of song system structures were found with other avian vocal learners. Motivated by questions of whether there are important differences in the vocal systems of parrots relative to other vocal learners, we used specialized constitutive gene expression, singing-driven gene expression, and neural connectivity tracing experiments to further characterize the song system of budgerigars and/or other parrots. We found that the parrot brain uniquely contains a song system within a song system. The parrot "core" song system is simi...
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... Exam-ples have been reported in which birds were heard singing with different volumes depending on the motivational state of the bird. ... 145 The result of the sp1. measurements is supported by measurements achieved with similar... more
... Exam-ples have been reported in which birds were heard singing with different volumes depending on the motivational state of the bird. ... 145 The result of the sp1. measurements is supported by measurements achieved with similar equipment by SVANE (pers. ...
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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... more
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 ...
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Animal personality research is receiving increasing interest from related fields, such as evolutionary personality psychology. By merging the conceptual understanding of personality, the contributions to both fields of research may be... more
Animal personality research is receiving increasing interest from related fields, such as evolutionary personality psychology. By merging the conceptual understanding of personality, the contributions to both fields of research may be enhanced. In this study, we investigate animal personality based on the definition of personality traits as underlying dispositional factors, which are not directly measurable, but which predispose individuals to react through different behavioural patterns. We investigated the shyness-boldness continuum reflected in the consistency of inter-individual variation in behavioural responses towards novelty in 47 farmed American mink (Neovison vison), which were raised in identical housing conditions. Different stages of approach behaviour towards novelty, and how these related within and across contexts, were explored. Our experimental design contained four tests: two novel object tests (non-social contexts) and two novel animated stimuli tests (social con...
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ABSTRACT In several avian and mammal social species, contact calls are hypothesized to function in maintaining group cohesion, coordinating activities between group members and negotiating fissions and fusions of multiple groups during... more
ABSTRACT In several avian and mammal social species, contact calls are hypothesized to function in maintaining group cohesion, coordinating activities between group members and negotiating fissions and fusions of multiple groups during foraging and roosting. They are therefore expected to exhibit acoustic features that make them suitable for communication of identity information. We investigated this in the monomorphic Peach-fronted Conure, a tropical parakeet living in open forest and scrubland habitats. The species is highly social outside the breeding season where it is assumed to live in a fission–fusion social system. In this study, contact calls from 10 visually isolated male and female Peach-fronted Conures were recorded outside the breeding season. Results from the multivariate analysis of variance and spectrographic cross-correlation with principal coordinates analysis procedure showed that contact calls varied highly between individuals and indicated that caller identity could be encoded in the duration, peak frequency, max frequency and 25%, 50% and 75% frequency energy quartiles of contact calls. The 50% frequency and 75% energy quartile was also significantly higher for females than for males. Furthermore, the results showed an inverse relationship between two morphometric measures and two spectral parameters, suggesting that variation in call parameters could also allow receivers to obtain information about the body size of the caller. Discriminant function analysis showed that contact calls could be correctly classified to individuals in 100% and to sexes in 91% of the cases, suggesting that there is sufficient variation in contact call parameters to enable vocal recognition of individuals and sex.
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Zoology and Bioacoustics
Strong social bonds can make an important contribution to individual fitness, but we still have only a limited understanding of the temporal period relevant to the adjustment of social relationships. While there is growing recognition of... more
Strong social bonds can make an important contribution to individual fitness, but we still have only a limited understanding of the temporal period relevant to the adjustment of social relationships. While there is growing recognition of the importance of strong bonds that persist for years, social relationships can also vary over weeks and months, suggesting that social strategies may be optimized over shorter timescales. Using biological market theory as a framework, we explore whether temporal variation in the benefits of social relationships might be sufficient to generate daily adjustments of social strategies in wild baboons. Data on grooming, one measure of social relationships, were collected from 60 chacma baboons (Papio ursinus) across two troops over a six month period. Our analyses suggest that social strategies can show diurnal variation, with subordinates preferentially grooming more dominant individuals earlier in the day compared with later in the day. These findings...
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Male sexual harassment of females is common across sexually reproducing species and can result in fitness costs to females. We hypothesized that females can reduce unwanted male attention by constructing a social niche where their female... more
Male sexual harassment of females is common across sexually reproducing species and can result in fitness costs to females. We hypothesized that females can reduce unwanted male attention by constructing a social niche where their female associates are more sexually attractive than themselves, thus influencing the decision-making of males to their advantage. We tested this hypothesis in the Trinidadian guppy ( Poecilia reticulata ), a species with high levels of male sexual harassment. First, we confirmed that non-receptive females were harassed less when they were paired with a more sexually attractive (receptive) female than with another non-receptive female. We then found that, indeed, females exploit this as a strategy to reduce sexual harassment; non-receptive females actively preferred to associate with receptive over non-receptive females. Importantly, when given access only to chemosensory cues, non-receptive females still showed this preference, suggesting that they use inf...
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The acoustic environment of swift foxes Vulpes velox vocalizing close to the ground and the effect of propagation on individual identity information in vocalizations were quantified in a transmission experiment in prairie habitat. Sounds... more
The acoustic environment of swift foxes Vulpes velox vocalizing close to the ground and the effect of propagation on individual identity information in vocalizations were quantified in a transmission experiment in prairie habitat. Sounds were propagated (0.45 m above the ground) at distances up to 400 m. Effects of transmission were measured on three sound types: synthesized sweeps with 1.3 kHz bandwidths spanning in the range of 0.3-8.0 kHz; single elements of swift fox barking sequences (frequency range of 0.3-4.0 kHz) and complete barking sequences. Synthesized sweeps spanning 0.3-1.6 and 1.2-2.5 kHz propagated the furthest and the latter sweeps exhibited the best transmission properties for long-range propagation. Swift fox barking sequence elements are centered toward the lower end of this frequency range. Nevertheless, measurable individual spectral characteristics of the barking sequence seem to persist to at least 400 m. Individual temporal features were very consistent to at least 400 m. The communication range of the barking sequences is likely to be farther than 400 m and it should be considered a long-ranging vocalization. However, relative to the large home ranges of swift foxes (up to 16 km(2) in the experimental area) the barking sequence probably functions at intermediate distances.
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In forests reverberations have probably detrimental and beneficial effects on avian communication. They constrain signal discrimination by masking fast repetitive sounds and they improve signal detection by elongating sounds. This... more
In forests reverberations have probably detrimental and beneficial effects on avian communication. They constrain signal discrimination by masking fast repetitive sounds and they improve signal detection by elongating sounds. This ambivalence of reflections for animal signals in forests is similar to the influence of reverberations on speech or music in indoor sound transmission. Since comparisons of sound fields of forests and concert halls have demonstrated that reflections can contribute in both environments a considerable part to the energy of a received sound, it is here assumed that reverberations enforce also birdsong in forests. Song elements have to be long enough to be superimposed by reflections and therefore longer signals should be louder than shorter ones. An analysis of the influence of signal length on pure tones and on song elements of two sympatric rainforest thrush species demonstrates that longer sounds are less attenuated. The results indicate that higher sound pressure level is caused by superimposing reflections. It is suggested that this beneficial effect of reverberations explains interspecific birdsong differences in element length. Transmission paths with stronger reverberations in relation to direct sound should favor the use of longer signals for better propagation.
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ABSTRACT The effects of bird song imply a transfer of information between conspecifics. This communication channel is constrained by habitat-induced degradation. Many studies suggest that birds can utilize features of degraded song to... more
ABSTRACT The effects of bird song imply a transfer of information between conspecifics. This communication channel is constrained by habitat-induced degradation. Many studies suggest that birds can utilize features of degraded song to assess relative distance to the signaller (ranging). The degradation of transmitted song in the wren Troglodytes troglodytes is quantified to assess the opportunities offered in received song for both information transfer and ranging. This quantification incorporates three measurable aspects of degradation: signal-to-noise ratio; excess attenuation; blur ratio. Each aspect varies more-or-less predictably with transmission distance, i.e., a criterion for ranging. Significant effects of speaker and microphone elevation indicate a potential for birds to optimize both the opportunity for information transfer and ranging by considering perch location. Song elements are the smallest units of a song being defined as a continuous trace on a sonagram. Main and second-order effects of element type indicate element-specific patterns of degradation which could be a crucial factor in communication in this species. The element variation within a full song offers the potential for effective information transfer over a range of relevant distances and a variety of transmission pathways. It similarly offers highly flexible ranging opportunities. (C) 1998 Acoustical Society of America.
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... I. R. K. Stewart and T. Burke, Department of Animal and Plant Sciences, Uni6ersity of Sheffield, Sheffield, United Kingdom. ... 1998) and both juvenile growth-rates and parental egg size in chinook salmon Onchorhynchus tshawytscha (DD... more
... I. R. K. Stewart and T. Burke, Department of Animal and Plant Sciences, Uni6ersity of Sheffield, Sheffield, United Kingdom. ... 1998) and both juvenile growth-rates and parental egg size in chinook salmon Onchorhynchus tshawytscha (DD Heath, CA Bryden, JM Shrimpton, GK ...
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Interactive playback experiments to singing male Great Tits Parus major were used to compare the effects of overlapping their songs with alternating playback which avoided such overlapping. The results showed that the means of measures of... more
Interactive playback experiments to singing male Great Tits Parus major were used to compare the effects of overlapping their songs with alternating playback which avoided such overlapping. The results showed that the means of measures of approach response and ...
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A new portable digital sound emitter (DSE) for normal and interactive playback of sound signals in the field and in the laboratory is described together with two examples of applications of the DSE in interactive field experiments. The... more
A new portable digital sound emitter (DSE) for normal and interactive playback of sound signals in the field and in the laboratory is described together with two examples of applications of the DSE in interactive field experiments. The DSE may be loaded with a broad spectrum of digitised sounds, e.g. artificial signals or natural animal vocalisations, and it is controlled
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... SAFI K. DARDEN', SIMON B. PEDERSEN AND TORBEN DABELSTEEN Department of Animal Behaviour and Centre for Sound Communication ... vocal tract causes selective resonance filtering (damping) and amplification resulting in formant... more
... SAFI K. DARDEN', SIMON B. PEDERSEN AND TORBEN DABELSTEEN Department of Animal Behaviour and Centre for Sound Communication ... vocal tract causes selective resonance filtering (damping) and amplification resulting in formant frequencies (eg, Riede & Fitch 1999 ...
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Transmission of acoustic signals through the habitat modifies the signals and may thus influence their use in communication. We investigated the transmission of five different types of whitethroat (Sylvia communis) vocalisations, three... more
Transmission of acoustic signals through the habitat modifies the signals and may thus influence their use in communication. We investigated the transmission of five different types of whitethroat (Sylvia communis) vocalisations, three types of song and two calls. Typical examples were broadcast and re-recorded in a whitethroat habitat with hedgerows and open meadow. We used a complete factorial design with speaker and microphone placed in different natural sender and receiver positions including high perches and song flights. Sound degradation was quantified in terms of signal-to-noise ratio, excess attenuation, tail-to-signal ratio and blur ratio. The results suggest that sound degradation generally increased with distance along a hedgerow, which means that birds here potentially may use degradation in assessing the distance to a vocalising individual. This is unlike the open meadow where the change in degradation with distance was negligible. Surprisingly, song flight relative to...
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Many species of songbirds appear to monitor the distance to conspecifics by attending to songs received from them (ranging). Features of the habitat-induced degradation of the song seem to provide the ranging cues. This study investigates... more
Many species of songbirds appear to monitor the distance to conspecifics by attending to songs received from them (ranging). Features of the habitat-induced degradation of the song seem to provide the ranging cues. This study investigates where, in a received, degraded song, the cues used for ranging lie; in the song elements, in the inter-element pauses or both. Examples of undegraded and degraded wren Troglodytes troglodytes song were cut into element and pause portions which were reassembled into four treatment types; two where the degradation between elements and pauses was concordant and two where either elements or pauses were degraded. These were played back at the boundaries of wren territories. The experiment was calibrated by measuring the degradation of the received playback songs and re-categorizing the trials into treatment types accordingly. Wrens responded to undegraded song by aggressively approaching and to degraded song with a less intense approach and an increase ...