Behavioural Processes

Deficits in response inhibition (i.e., the ability to suppress inappropriate responses) may contribute to increased impulsive aggression (i.e., unplanned behaviors that harm others). Since early-life environment might influence the development of response inhibition, it could also indirectly affect impulsive aggression. However, this relationship has rarely been directly examined. Here, we investigated whether response inhibition is associated with impulsive aggression and whether this relationship explains the effects of early-life social environments on impulsive aggression in juvenile Japanese quails (Coturnix japonica). Quails (n = 120) were raised in two social conditions: Small groups of five birds or Large groups of 15 birds. Response inhibition was assessed using the Barrier and Cylinder tasks, while impulsive aggression was measured in two contexts - within a group of five familiar individuals and in a dyad with an unfamiliar individual. We found that some aspects of response inhibition were related to impulsive aggression. Furthermore, quails reared in small groups showed significantly poorer response inhibition than those reared in large groups. Yet, impulsive aggression did not significantly differ between the two conditions. These findings suggest that, while impulsive aggression is partly related to response inhibition, other factors mitigate the effects of early social environments on its expression.

A wide range of non-human animal species have been shown to be able to respond to human referential signals, such as pointing gestures. The aim of the present study was to replicate previous findings showing cats to be sensitive to human pointing cues (Miklosi et al. 2005). In our study, we presented two types of human pointing gestures - momentary ipsilateral (direct pointing) and momentary cross-body pointing. We tested nine rescue cats in a two-way object choice task. On a group level, the success rate of cats was 74.4 percent. Cats performed significantly above chance level in both the ipsilateral and cross-body pointing condition. Trial number, rewarded side and type of gesture did not significantly affect the cats performances in the experiment. On an individual level, 5 out of 7 cats who completed 20 trials, performed significantly above chance level. Two cats only completed 10 trials. One of them succeeded in 8, the other in 6 of these. The results of our study replicate previous findings of cats being responsive to human ipsilateral pointing cues and add additional knowledge about their ability to follow cross-body pointing cues. Our results highlight that a domestic species, socialised in a group setting, may possess heterospecific communication skills. Further research is needed to exclude alternative parsimonious explanations, such as local and stimulus enhancement.

Birdsong is an important communication signal used in mate choice. In some songbirds, only males produce songs while females do not. Female birds are sensitive to inter- and intra-species song variation. Some aspects of female song preference depend on developmental experiences. For example, in Bengalese finches and zebra finches, adult females prefer the song to which they were exposed early in life, such as the fathers song. However, it is unclear whether such song preference in females is sexually motivated. The purpose of our study is to test if female Bengalese finches recognize their fathers song as sexually attractive. We measured copulation solicitation displays during playbacks of the fathers song vs. unfamiliar conspecific songs and found that across individuals, the fathers song elicited more displays than other songs. In addition, we analyzed if a birds response to a given song could be predicted by the level of similarity of that song to the fathers song. The results suggest that preference for the fathers song in this species is actually relevant to mate choice. Although more precise control is necessary in future studies to elucidate the process of preference development, our results imply the significance of early-life experience in shaping female song preference.

Animals differ in their ability to learn. One potential factor contributing to learning differences is personality types. We investigated the relationship between learning and the bold-shy continuum by comparing performance of bold and shy zebrafish in conditioned place preference (CPP) and 2 choice tasks. Bold fish learned significantly faster than the shy fish but there were no differences in their final performance. When tested in the 2 choice task, we found no clear evidence of learning, however bold fish made more initial choices than shy fish. Overall,our study suggests that bold fish tend to be faster learners when compared to shy fish. The lack of differences in the final change in behavior suggests that the learning difference is due to neophobic tendencies and resulting initial interactions with the learning stimulus.

Previous studies suggest that vocal-learning species use variations of prosodic cues, such as changes in pitch, amplitude, or duration, in the conveying of meaning and emotions as well as individual recognition. Although it is known that the long-distance contact calls ("phee" calls) of common marmosets, a vocal non-learner, vary in prosodic information depending on individual characteristics, evidence of the species use of this information only recently started to emerge. In this study we tested 18 captive common marmosets (Callithrix jacchus) reactions to playbacks of familiar and unfamiliar individuals phee calls and extracted pitch-contour information. The playbacks consisted of i) natural phee calls from group members or unfamiliar conspecifics, or ii) synthesized pitch contours of familiar or unfamiliar phee calls following a natural or artificial syllable order as well as pure tones of similar frequency and duration. We found that although individuals seemed to show different reactions towards the natural calls of familiar and unfamiliar individuals, we did not find group level differences. Marmosets furthermore show significantly reduced interest in synthesized pitch contours compared to natural phee calls and did not differentiate between pitch contour playbacks and pure tone control stimuli, indicating that they did not categorize the pitch contours as conspecific calls. Our results suggest that extracted pitch contour information alone is not sufficient for marmosets to recognise conspecifics, however further studies are required to investigate the exact mechanism of individual recognition in marmosets.

Songbirds are renowned for their complex vocal communication abilities; among them, zebra finches (Taeniopygia guttata) are a key species for studying vocal learning and communication. Zebra finches use various calls with different meanings, including the distance call, which is used for long-distance contact. Whether these calls are static with fixed meanings or flexible remains an open question. In this study we aimed to answer this question by designing a novel behavioral paradigm, in which we trained food-restricted zebra finches to use distance calls for food request. Nine out of ten birds learned this association and used their distance calls to obtain food when they were hungry. We then introduced a visually-separated audience and compared the distance calls used for food requests with those used for communication between birds. Results revealed significant acoustic differences in power, pitch, and other spectral characteristics between the distance calls uttered in these two contexts. Our findings suggest that zebra finches can use their distance call for different goals and also acoustically modulate it based on the context. Therefore, it demonstrates a level of vocal control thought to be exclusive to songs. This study enhances our understanding of vocal flexibility and its role in vocal communication.

The ability to regulate and withhold an immediate behaviour in pursuit of a more preferred or valuable, albeit delayed, outcome is regarded as an important cognitive ability enabling adaptive decision-making in both social and asocial contexts. Abilities to cope with a delay in gratification have been investigated in a range of species using a variety of experimental paradigms. The present study attempts a first systematic evaluation of available experimental data from non-human animals, which is an essential basis for quantifying biological and non-biological factors (e.g. socio-ecology versus experimental design) affecting performance in delay of gratification tasks. Data were sourced from 52 separate studies, and a comprehensive overview of the available literature on delay of gratification in non-human animals is presented. We present data from 21 species, spanning across eight taxonomic order, with 1-9 species tested per taxonomic group. We highlight variation in experimental paradigms used to study delay of gratification abilities in non-human animals, both with regard to reward type or experimental setup, and discuss the implications for comparative analyses. We conclude that, at present, cross-species comparisons of delay of gratification abilities are hindered by a lack of consistency in experimental designs and low number of species tested across taxonomic orders. We hope to stimulate research on a more diverse set of species, and that future studies consider potential social and ecological factors that cause intra-specific variation in test performances, that is repeatedly seen across species.

Siamese fighting fish, Betta splendens, have been extensively studied due to their aggression and stereotypical displays. Many studies have focused on their characteristic opercular flaring, while the less aggressive and less energetically costly lateral display have been comparatively understudied. Many factors have been shown to influence aggression in Bettas, notably body length and the personality trait of boldness, however, the role that colour plays in determining an individuals aggressiveness is much less clear. The role of colour has only been briefly studied, and based on human interpretations of colour, i.e. limited to what the receivers eyes and sensory systems actually can process and discriminate, with results suggesting blue males are more aggressive than red males. Using male-male interactions, measuring opercular flaring and lateral display we found that colour and personality do play a role in determining the degree of aggressiveness in Betta splendens. Blue-finned males were more aggressive, performing longer lateral displays more frequently. Blue fins are a phenotype observed in wild type males and is likely selected for to allow visual cues to travel through the murky water they inhabit. Body mass was positively correlated with lateral display frequency, and opercular flare frequency and duration. Finally, neophobic individuals - individuals that were less willing to approach a novel object - were more aggressive, performing significantly more lateral displays. This indicates that personality may impact fighting strategy, with males either choosing to end conflicts quickly with more aggressive displays or to outlast their opponent with less energetically costly displays.

The "two-system" framework of fear proposed by LeDoux and Pine (2016) sparked a discussion on the understanding of fear, prompting a reevaluation of rodent fear conditioning studies. We propose that 22kHz ultrasonic vocalizations (USV) may symbolize the subjective negative emotional states in rats. To evaluate this, we designed a series of fear conditioning experiments with varied parameters, comparing the expression of 22kHz USV and body freezing - a traditional fear index. These expressions were further assessed in fear generalization tests. Our findings suggest a distinct separation between body freezing and 22kHz vocalizations in fear conditioning under different conditions. The results indicate that 22kHz USV may more accurately signify the subjective state of fear, whereas body freezing may denote an automatic defensive response in rats. Consequently, we posit that the two-system fear framework may extend to rodent fear conditioning paradigms. Therefore, researchers should place greater emphasis on 22kHz vocalizations when investigating the subjective state of fear.

Previous research has shown that humans can discriminate two individual rhesus monkeys (Macaca mulatta), as well as two individual zebra finches (Taeniopygia guttata) by their vocalizations. The discrimination of individual zebra finches largely relies on differences in pitch contour, although this is not the only relevant cue. The purpose of the present experiment was to examine whether humans can also discriminate two individual large-billed crows (Corvus macrorhynchos) by their calls. Discrimination was tested with a forced-choice Same-Different Paradigm. Results show a high discrimination accuracy without prior training, although the scores obtained here were lower than those in the zebra finch discrimination task. There was no significant learning trend across trials. Future studies should investigate which acoustic cues participants use for the discrimination of individual crows and expand these findings with more non-human animal vocalizations.

In some species, such as chameleon and cichlid fish, rapid body colouration changes (within seconds or minutes) serve as visual social signals in male-male competition. This study investigated the relationship between aggressive behaviour and body colouration changes in Oryzias celebensis, an Indonesian medaka fish. We analysed aggressive behaviours and corresponding body colouration changes during attack events in a controlled laboratory setting using groups of 3 adult fish in a small tank. In a triadic relationship consisting of 2 males and a female, males with blackened markings attacked more frequently than males without blackened markings and females. Additionally, we observed that the males with blackened markings were seldom attacked by males without blackened markings and females. These tendencies persisted even in groups consisting of 3 males. Our results suggest that the blackened markings in male O. celebensis not only indicate the level of aggression but also serve as a social signal to suppress attacks by other individuals.

Delayed development is a widespread evolutionary strategy that can reduce competition among highly social animals. Many seabirds exhibit delayed plumage maturation, in which young birds spend years in visually distinct predefinitive plumages before attaining the definitive plumage of adults. Previous work hypothesized that predefinitive plumages may function to reduce aggression towards young, predefinitive seabirds at breeding colonies, an idea known from other lineages of birds as the status signaling hypothesis. We tested this hypothesis with visual stimulus experiments at a breeding colony of American Herring Gulls (Larus smithsonianus). We presented painted models of four diYerent plumage classes (first-cycle predefinitive gull plumage, third-cycle predefinitive gull plumage, definitive gull plumage, and a Canada Goose as a control) and measured the aggressive responses of breeding adults at their nests. Breeding gulls responded with significantly less frequent, lower, and slower aggression toward the first-cycle and control plumages compared to the definitive plumage. There were no significant diYerences in response towards the third-cycle plumage. These results oYer support for a status signaling hypothesis, indicating that substantial, mottled brown plumage--as worn by first-cycle gulls--reduces aggression from breeding adults in colonies or foraging flocks. Future research can investigate how immature seabirds--including third-cycle gulls--may combine plumage, posture, and behavior to shift the dynamics of social behavior at breeding colonies.

Same-sex affiliative relationships are common in humans and some social animals, forming one of the bases of group living. The neuropeptide vasopressin (VP) and its receptors mediate these relationships and behaviours in mammals and birds with gregarious and colonial social structures. In some species, affiliative relationships between dominant and subordinate individuals can be maintained while still retaining strict dominance hierarchies where three or more individuals interact. However, it is unclear whether triadic interaction promotes these relationships, and whether the VP system is also involved in such affiliations due to the lack of suitable animal models and experimental settings. This study addresses these questions with two experiments. In Experiment 1, two-week cohabitation among three male crows facilitated affiliative relationships in particular dyads within each triad. In Experiment 2, vasopressin 1a receptor (V1aR) antagonism disrupted affiliative behaviours and led to the resurgence of agonistic behaviours in affiliated males but not in unaffiliated ones by peripherally administering a V1aR antagonist. These findings suggest that the VP system might universally mediate same-sex affiliative relationships, despite differences in inherent aggression levels among individuals. The triadic cohabitation paradigm established here could advance our understanding of animal societies and be applied across various species, sexes, and social structures. Impact statementThis study provides evidence that a triadic interactive environment facilitates the formation of affiliative relationship between specific dominant and subordinate males in large-billed crows, with crucial involvement of vasopressin 1a receptor in maintaining this affiliation.

Among species reproducing sexually, mating strategies represent a major component of individual fitness. The major histocompatibility complex (MHC) is an extremely diverse set of genes responsible for immunological recognition and defence against pathogens. Although dissimilarity between mates at the major histocompatibility complex has been proposed to drive mate choice through increased offspring pathogen resistance, evidence is mixed. In addition, explorations of the role of the major histocompatibility complex in other mating strategies, such as divorce, are rare. We investigated whether dissimilarity at the major histocompatibility complex class IIB is associated with mate choice and divorce probability in the genetically monogamous black-legged kittiwake (Rissa tridactyla). We found that first-time male breeders, as well as divorced males, were paired with females more dissimilar at the major histocompatibility complex class IIB than expected under random mating. We did not find evidence for mate choice based on major histocompatibility complex class IIB dissimilarity when considering females. In addition, in the studied population, divorce probability was very low compared with other populations and did not significantly vary with the dissimilarity of the pair at the major histocompatibility complex class IIB. Our results pave the way to a better understanding of the complex role of major histocompatibility complex dissimilarity in mating decisions of species displaying mutual choice and biparental care.

Eurasian jays (Garrulus glandarius) do not habitually use tools, yet they can be trained to solve object-dropping tasks, i.e. to insert a tool into an apparatus to release a food reward. Previous research suggests the these jays can learn a preference toward functional tools - objects allowing to obtain a food reward placed inside an apparatus - according to their density (Cheke et al., 2011). However, it is not yet known whether they can also select functional tools (tool selectivity) according to other physical properties such as size and shape, and use different kinds of tools to solve a similar task. Here we conducted three object-dropping experiments aimed at exploring these abilities in Eurasian jays. In Experiment 1, jays tended to select large stones as tools irrespective of the diameter of the apparatus. However, jays progressively developed a preference for the small tool, which was functional with both the wide and the narrow apparatuses. In Experiment 2, only vertically-oriented long stones could fit into the narrow apparatus, whereas both long and round stones were functional with the wide apparatus. Jays showed a preference for the long stone and, with the narrow apparatus, tended to achieve the correct manipulation after one or more unsuccessful attempts. In Experiment 3, jays were able to use sticks and adopt a novel technique on the same object-dropping apparatus, thus providing the first evidence that Eurasian jays can use sticks as tools. Taken together, these results indicate that Eurasian jays may have limited tool selectivity abilities but nonetheless can use different kinds of tools to solve similar tasks.

Courtship songs in mice have been investigated to understand the mechanisms and ecological relevance of vocal communication. There is evidence that courtship song characteristics vary between different genotypes, but little is known on whether individuals, even within the same genotype, differ from each other in the composition, complexity, and temporal consistency of their songs. In a first study, we aimed to systematically identify song features typical of different genotypes, by assessing the composition and complexity (i.e., entropy) of the syllabic sequences of male laboratory mice from four different strains (Mus musculus f. domestica: C57BL/6J, BALB/c, DBA/2 and B6D2F1). Mice were individually presented with a swab containing fresh female urine for 5 minutes to elicit courtship songs. The four strains differed not only in the composition but also in the complexity of their syllabic sequences. In a second study, we investigated within-strain individual differences in temporal consistency and recurring motifs (i.e., identical sets of syllables that are repeated within a song), using BALB/c and DBA/2 mice. The same procedure as in the first study was followed, but in addition testing was repeated weekly over three weeks. Both strains showed some level of individual temporal consistency; BALB/c in the overall amount of emitted vocalisations and DBA/2 in the expression of specific syllable types. However, hierarchical cluster analysis revealed remarkable individual variability in how consistent song characteristics were over time. Furthermore, recurring motifs were expressed at varying levels depending on the individual. Taken together, not only genotype but also individuality can affect variability in courtship songs in mice, suggesting the existence of different courtship strategies (e.g., higher song consistency to facilitate individual identification) related to varying levels of behavioural plasticity. HIGHLIGHTSO_LICourtship songs in mice can serve as a model to study vocal communication C_LIO_LIWe explore how genotype and individuality affect courtship songs characteristics C_LIO_LIGenotypes differ in composition and also in complexity of syllabic sequences C_LIO_LIWe find remarkable individual variability in how consistent songs are over time C_LIO_LIResults suggest the existence of variation in male courting behaviour C_LI

Social isolation affects the brain and behavior in a variety of animals, including humans. Studies in traditional laboratory rodents, including mice and rats, have supported the idea that short-term social isolation promotes affiliative social behaviors, while long-term isolation promotes anti-social behaviors, including increased aggression. Whether the effects of isolation on the social behaviors of mice and rats generalize to other rodents remains understudied. In the current study, we characterized the effects of short-term (3-days) social isolation on the vocal and non-vocal social behaviors of adult prairie voles (Microtus ochrogaster) during same-sex and opposite-sex social interactions. Our experiments revealed that short-term isolation did not affect rates of ultrasonic vocalizations or time spent in non-aggressive social behaviors and huddling. In contrast, short-term isolation affected aggression in a sex- and context-specific manner during male-male interactions. Our findings highlight the importance of comparative work across species and the consideration of social context to understand the diverse ways in which social isolation can impact social behavior.

Social recognition has been studied and demonstrated in many species. In domesticated species, the long evolutionary history shared with humans has led to investigations into their cognitive abilities towards humans, particularly regarding discrimination and recognition of humans. The present study investigated whether cows are capable of visual discrimination and cross-modal recognition of familiar and unfamiliar humans. Thirty-two cows were exposed to two tests: a visual preference test, during which two silent videos were shown simultaneously - each displaying either a familiar or an unfamiliar human face - and a cross-modal test, during which the videos were accompanied by either a congruent or incongruent voice. During the visual preference test, cows looked significantly longer at the video showing the unfamiliar person (p = 0.025). In the cross-modal test, they looked significantly longer at the video that was congruent with the voice being played (p = 0.021). These two results show that cows are able to discriminate between familiar and unfamiliar individuals and form cross-modal representations of these people. Based on these results, future research should explore whether cows can adjust their behaviour depending on the person they are interacting with - a capacity that may reflect their agency in human-animal relationships.

Birds can assess nest predation risk and adjust their parental activity accordingly. Risk taking behavior should be related to investment in reproduction as well as to confidence in parenthood that often differ between sexes. In those cases, sexual differences in risk taking behavior may be expected. For example, in blue tits, females invest more time and energy than males in nest-building, egg laying and incubation. Furthermore, confidence in parenthood is supposed to be higher for females, as extrapair paternity is common in this species. Therefore, the reproductive value of nestlings may be higher for females than for males and the former may assume greater risks to ensure nestling growth and maximize their reproductive success. We examined potential sexual differences in the risk assumed by parents in relation to perceived risk of predation inside the nest cavity, where predation risk perception may be higher. We increased perceived predation risk by adding predator chemical cues inside blue tit (Cyanistes caeruleus) nest-boxes, and we tested whether female and male parents differed in the risk assumed when taking care of nestlings. Females and males did not differ in the risk assumed in response to perceived predation risk. However, females reduced time devoted to nest sanitation activities when predator chemical cues were detected inside the nest-box, likely as an anti-predatory strategy to minimize their own risk of predation. Therefore, these results add to the evidence that birds can detect chemical cues of predators inside the nest cavity and suggest that the behavioral response to an increase in risk of predation perceived through olfactory cues is not sex-dependent in blue tit.

Humans show distinct social behaviours when we recognise social similarity in opponents that are members of the same social group. However, little attention has been paid to the role of social similarity in non-human animals. In Wistar subject rats, the presence of an unfamiliar Wistar rat mitigated stress responses, suggesting the importance of social similarity in this phenomenon. We found that the presence of unfamiliar Sprague-Dawley (SD) or Long-Evans (LE) rats, but not an unfamiliar Fischer 344 (F344) rat, similarly mitigated stress in subject rats. It is therefore possible that the subject rats recognised social similarity to unfamiliar SD and LE rats. In this study, we demonstrated that Wistar subject rats were capable of categorizing unfamiliar rats based on their strain, and that Wistar subjects showed a preference for unfamiliar Wistar, SD, and LE rats over F344 rats. However, the subject rats did not show a preference among Wistar, SD, and LE rats. In addition, the results were not due to an aversion to F344 rats, and preference was not affected when anaesthetised rats were presented to subject rats. The findings suggested that rats recognise social similarity to certain unfamiliar strains of rats.