Vocal Expression of Emotions in Mammals: Mechanisms of Production and Evidence

Emotions play a crucial role in an animal’s life because they facilitate responses to external or internal events of significance for the organism. In social species, one of the main functions of emotional expression is to regulate social interactions. There has recently been a surge of interest in animal emotions in several disciplines, ranging from neuroscience to evolutionary zoology. Because measurements of subjective emotional experiences are not possible in animals, researchers use neurophysiological, behavioural and cognitive indicators. However, good indicators, particularly of positive emotions, are still lacking. Vocalizations are linked to the inner state of the caller. The emotional state of the caller causes changes in the muscular tension and action of its vocal apparatus, which in turn, impacts on vocal parameters of vocalizations. By considering the mode of production of vocalizations, we can understand and predict how vocal parameters should change according to the arousal (intensity) or valence (positive/negative) of emotional states. In this paper, I review the existing literature on vocal correlates of emotions in mammals. Non-human mammals could serve as ideal models to study vocal expression of emotions, because, contrary to human speech, animal vocalizations are assumed to be largely free of control and therefore direct expressions of underlying emotions. Furthermore, a comparative approach between humans and other animals would give us a better understanding of how emotion expression evolved. Additionally, these non-invasive indicators could serve various disciplines that require animal emotions to be clearly identified, including psychopharmacology and animal welfare science

Goats excel at learning and remembering a highly novel cognitive task

PMCID: PMC398717

Correction: assortative mating in fallow deer reduces the strength of sexual selection.

PMCID: PMC3182158 This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.This article corrects this one: PLoS One. 2011; 6(4): e18533. doi:10.1371/journal.pone.0018533[This corrects the article on p. e18533 in vol. 6.]

Behaviour of Horses in a Judgment Bias Test Associated with Positive or Negative Reinforcement

Moods can influence our judgment of ambiguous stimuli as positive or negative. Measuring judgment bias in animals is a promising method to objectively assess their emotional states. Our study aimed to develop a cognitive bias test in horses, in order to assess the effect of training using positive reinforcement (PR) or negative reinforcement (NR) on their emotional states. We trained 12 mares to discriminate between a rewarded and a non-rewarded location situated on each side of a paddock. The mares were then trained during five days to perform several exercises using PR (n = 6) for one group, and NR (n = 6) for the other (treatment). Finally, we compared the responses of the two groups to three ambiguous locations situated between the rewarded and non-rewarded locations (judgment bias test). During the training exercises, according to our predictions, behavioural measures suggested that NR mares experienced more negative emotions than PR mares. Surprisingly, the results of the judgment bias test suggest that NR mares were in a more optimistic mood compared to PR mares, despite previously experiencing more negative emotions during the treatment. NR mares could have been more motivated to obtain a food reward than PR mares, which had been rewarded throughout the treatment phase. Alternatively, NR mares could have developed optimistic bias triggered by release from the negative state experienced during treatment. This first attempt to test judgment bias in horses suggests that this is a promising method to measure horse mood. Knowledge about the effect of training methods on the mental health of domesticated animals can add a new dimension to animal welfare, in order to promote better ways to work with animals

Is there any evidence for vocal learning in chimpanzee food calls?

In their study “Vocal Learning in the Functionally Referential Food Grunts of Chimpanzees”, Watson et al. [1] claimed that they “provide the first evidence for vocal learning in a referential call in non-humans”. We challenge this conclusion, on two counts. For one, we are not convinced that the authors controlled for arousal (or at least they did not report such data); furthermore, the vocal characteristics of the two groups largely overlapped already at the beginning of the study. Accordingly, we also question the authors’ claim that their finding “sheds new light on the evolutionary history of human referential words”

Microdialect and Group Signature in the Song of the Skylark Alauda arvensis

The Skylark Alauda arvensis is a territorial species of open landscape in which pairs settle in stable and adjacent territories during the breeding season. Due to the heterogeneity of the habitat, territories are gathered in patches spaced by a few kilometres, in which each male produces very long and complex flight songs as a part of the territorial behaviour. We showed that, in a given patch, all the males (neighbours) share some particular sequences of syllables in their songs, whereas males settled in different patches (strangers) have almost no sequences in common. Such a phenomenon is known as microdialect. To test the hypothesis that these shared sequences support a group signature, we made playback experiments with ‘‘chimeric’’ signals: songs of strangers where the sequences shared by neighbours were artificially inserted. Behavioural responses to playbacks indicated a neighbour-stranger discrimination consistent with the dear enemy phenomenon, i.e. a reduced aggression toward neighbours compared to strangers. Furthermore, the same level of responses, observed when a ‘‘chimeric’’ song and a neighbour song were broadcast, indicated that shared sequences are recognized and identified as markers of the neighbourhood identity

Fallow deer polyandry is related to fertilization insurance

Polyandry is widespread, but its adaptive significance is not fully understood. The hypotheses used to explain its persistence have rarely been tested in the wild and particularly for large, long-lived mammals. We investigated polyandry in fallow deer, using female mating and reproduction data gathered over 10years. Females of this species produce a single offspring (monotocous) and can live to 23years old. Overall, polyandry was evident in 12% of females and the long-term, consistent proportion of polyandrous females observed, suggests that monandry and polyandry represent alternative mating strategies. Females were more likely to be polyandrous when their first mate had previously achieved high numbers of matings during the rut or was relatively old. However, polyandry was not related to the following factors: female age, the stage of the rut, the dominance ranks of mates, or the number of daily matings achieved by males. Polyandrous and monandrous multiple-mating females were not more likely than single-mating females to be observed with an offspring during the following year, and there were no significant differences in offspring size between these females. These results provide support for a fertility insurance hypothesis, with females remating if fertilization from the first mating was uncertain due to possible sperm depletion. The potential for different female mating strategies among large, polygynous mammals has generally been overlooked. Our findings highlight the complexity of female reproductive strategies and the possible trade-offs between fertilization success, preferences for high-quality males, and potential costs of polyandry, particularly for monotocous specie

Quality prevails over identity in the sexually selected vocalisations of an ageing mammal

BACKGROUND: Male sexually selected vocalisations generally contain both individuality and quality cues that are crucial in intra- as well as inter-sexual communication. As individuality is a fixed feature whereas male phenotypic quality changes with age, individuality and quality cues may be subjected to different selection pressures over time. Individuality (for example, morphology of the vocal apparatus) and quality (for example, body size and dominance status) can both affect the vocal production mechanism, inducing the same components of vocalisations to convey both kinds of information. In this case, do quality-related changes to the acoustic structure of calls induce a modification of vocal cues to identity from year to year? We investigated this question in fallow deer (Dama dama), in which some acoustic parameters of vocalisations (groans) code for both individuality and quality. RESULTS: We carried out a longitudinal analysis of groan individuality, examining the effects of age and dominance rank on the acoustic structure of groans of the same males recorded during consecutive years. We found both age- and rank-related changes to groans; the minimum values of the highest formant frequencies and the fundamental frequency increased with the age of males and they decreased when males became more dominant. Both age- and rank-related acoustic parameters contributed to individuality. Male quality changed with age, inducing a change in quality-related parameters and thus, a modification of vocal cues to male individuality between years. CONCLUSIONS: The encoding of individuality and quality information in the same components of vocalisations induces a tradeoff between these two kinds of signals over time. Fallow deer vocalisations are honest signals of quality that are not fixed over time but are modified dynamically according to male quality. As they are more reliable cues to quality than to individuality, they may not be used by conspecifics to recognize a given male from one year to another, but potentially used by both sexes to assess male quality during each breeding season