Acoustic displays are conspicuous behaviours common across diverse animal taxa. They have long been studied in behavioural ecology, evolutionary biology and neuroscience. Most of these investigations, however, have focused on male display. For species in which both sexes display, correcting this bias will lead to a fuller understanding of the evolution and function of these behaviours. In this study, we investigated the role of vocal advertisement display in female Alston's singing mice, . Singing mice are small muroid rodents of the family Cricetidae, native to high=altitude cloud forests of Central America. Females and males both produce elaborate advertisement songs, known in males to be used in mate attraction and intrasexual competition. Prior studies have largely focused on male behaviour, although we recently found that both sexes dramatically increase their rate of singing and song duration in response to playback of conspecific male song. Here, we tested how mice of both sexes adjust their song effort in response to female song playback. Our results show that, like male song, female song elicits robust increases in song effort from both female and male mice. This study reveals additional social contexts that promote high song effort in this species, while raising further questions about the role of song in communication within and between the sexes.

Behavioural mating choices and mating success are important factors in the development of reproductive isolation during speciation. Environmental conditions, especially temperature, can affect these key traits. Environmental conditions can vary across, and frequently delimit, species' geographical ranges. Pairing suboptimal conditions with relative rarity of conspecifics at range margins may set the stage for hybridization. Despite the importance of mating behaviours as a reproductive barrier, a general understanding of the interaction between behavioural choices and the environment is lacking, in part because systematic studies are rare. With this report, we begin to bridge that gap by providing evidence that temperature has a significant but inconsistent influence on mating choices and success and, thus, on reproductive isolation in . We studied mating propensity and success at four different temperatures among 14 species in no-choice conspecific mating trials and in heterospecific trials among two species triads that are known to regularly hybridize in the wild. We found that mating frequency varied significantly across a 10 °C range (from 18 °C to 28 °C), both in 1:1 mating trials and in high-density en masse trials, but that the effect of temperature was highly species specific. We also found that mating frequency was consistently low and that temperature had a moderate effect on some heterospecific crosses. As conspecific mating propensity decreased outside of the optimal thermal range, while heterospecific matings remained constant, the proportion of heterospecific matings at suboptimal temperatures was relatively high. This result indicates that temperature can modulate behavioural choices that impose reproductive barriers and influence the rate of hybridization. More broadly, our results demonstrate that to truly understand how mating choice and reproductive isolation occur in nature, they need to be studied in an environmental context.

The effect of the social environment on the proinflammatory immune response may mediate the relationship between social environment and fitness but remains understudied outside captive animals and human populations. Age can also influence both immune function and social behaviour, and hence may modulate their relationships. This study investigates the role of social interactions in driving the concentrations of two urinary markers of proinflammatory immune activation, neopterin and soluble urokinase plasminogen activator receptor (suPAR), in a free-ranging population of rhesus macaques, . We collected 854 urine samples from 172 adult monkeys and quantified how urinary suPAR and neopterin concentrations were related to affiliative behaviour and agonistic behaviour received over 60 days. In females, but not in males, higher rates of affiliative interactions were associated with lower neopterin concentrations, while conversely, experiencing more agonistic interactions was associated with higher neopterin concentrations. The association between affiliation and neopterin concentration was modulated by age, with older females experiencing a stronger negative association between affiliative behaviour and neopterin concentration. There were no associations between suPAR concentration and social environment for either sex. This study demonstrates that proinflammatory immune activity is a potential mechanism mediating the association between social environment and fitness under naturalistic conditions and that age can be an important modulator of the effect of social environment on the immune system.

Strong, affiliative bonds often function to facilitate social competition through cooperative defence of resources, but the benefits of social bonds may be low when direct competition is less intense or less beneficial. In such cases, one possible outcome is that relationships are weak and undifferentiated. Alternatively, negotiating stable, selectively tolerant relationships may be a strategy to mitigate the costs and risks of sharing space when direct competition is undesirable. We investigated dyadic social tolerance among wild adult female chimpanzees, who engage in low rates of affiliation and aggression amongst one another. While females associate with one another at different rates, these patterns could reflect shared patterns of behaviour (e.g., ranging) rather than social preference or variation in relationship quality. We first determined whether patterns of dyadic spatial association (five-meter proximity) were differentiated and stable over time. To assess whether dyadic spatial association reflected preference and variation in social tolerance, we tested whether spatial association was actively maintained by waiting and following behaviour, and associated with decreased aggression and increased cofeeding. Spatial associations were differentiated, and stronger associations were more stable. Frequent associates used following and waiting behaviour to actively maintain associations. Association positively predicted time cofeeding and negatively predicted aggression. These patterns were true among related and unrelated dyads. Among unrelated females, dyads with stronger associations maintained proximity more mutually. This study highlights social tolerance as a stable relationship attribute that can predict and explain patterns of behaviour and social network structure, distinct from, or in the absence of, affiliation.

The Vandenbergh effect, or male-mediated maturation, occurs when females reach sexual maturation upon exposure to a novel male. Male-mediated maturation is found across mammals, including in geladas, , where it may be an adaptive counterstrategy to infanticide that follows the immigration of a new male; maturing after male immigration maximizes a female's chances of weaning her first offspring before the next infanticidal male immigrates (the 'optimal timing hypothesis'). Alternatively, the nonadaptive 'Bruce effect by-product hypothesis' posits that male-mediated maturation in geladas (and possibly other mammals) is triggered by the same physiological changes that, in pregnant females, produce spontaneous abortion (the Bruce effect). We test both hypotheses using theory and observational data. We show that neither male-mediated maturation nor its associated hormonal changes occur in baboons ( × ), a primate without the Bruce effect. An individual-based model suggests that male-mediated maturation should not evolve via adaptive evolution in either geladas or baboons. Finally, we derive the selection coefficient for male-mediated maturation and show it is likely to be very small because male-mediated maturation yields only marginal potential benefits unless the system is extremely fine-tuned. We conclude that male-mediated maturation in geladas is a by-product of the Bruce effect and more broadly that the Vandenbergh effect may be nonadaptive.

The navigational mechanisms of homing pigeons, , have been extensively studied and represent a useful model for the navigation of birds and other animals. Pigeons navigate with an olfactory map and sun compass from unfamiliar areas and, in familiar areas, are largely guided by visual landscape cues, following stereotyped and idiosyncratic routes. However, the mechanisms by which they gain familiarity, improve their navigation and transition between navigational strategies during learning are not fully understood. Addressing these outstanding questions in this navigational model will help to improve our understanding of navigational ontogeny. We sought to investigate whether passive exposure to the cues at a site, without release, was sufficient for navigational learning, given that pigeons can determine the home direction before taking off. We exposed pigeons to cues at a novel site before returning them to the site the next day and releasing them alongside controls. We found no differences in the directional distributions, mean vector lengths, virtual vanishing times, efficiency indices or homing efficiency indices between birds that had and had not previously visited the site. We therefore found no evidence to suggest that passive exposure to the cues at a novel site was sufficient to facilitate a detectable improvement in navigational performance. There are three possible explanations for this result: first, a larger sample size would have detected a weak effect of learning; second, passive exposure to a release site is insufficient to generate navigational learning; and third, pigeons learn from passive exposure but do not rely upon this information, showing no difference in performance, despite learning. We discuss these three explanations with reference to previous findings on navigational learning in homing pigeons. We suggest that experiments should continue to examine navigational ontogeny in homing pigeons to help address this major problem for the field of navigation.

Because senescence impairs the ability of older males to compete successfully for mates, male reproductive strategies are expected to change with age. The terminal investment hypothesis proposes that older males, who could die soon, should take greater risks to obtain mating opportunities. Another possibility is that older males avoid such risks, adopting alternative reproductive tactics, such as increased affiliation with females, increased reliance on coalitions or sexual coercion to continue to compete with younger animals. We tested these hypotheses in wild chimpanzees, , of the Kanyawara community, Kibale National Park, Uganda, where old males sire offspring at relatively high rates. Our data set included >40 000 incidents of male aggression and >5800 copulations observed between 2005 and 2017. We found that, even as their dominance status declined, old males maintained relatively high copulation rates, especially with established mothers. There was no evidence for terminal investment in response to ageing. Males became generally less aggressive as they aged. Neither did old males form affiliative bonds with females, nor use sexual coercion more frequently, as alternative reproductive tactics. Old males did, however, participate in coalitionary aggression at higher rates than young males and increased the proportion of their aggression that was coalitionary over time. Coalitions were positively associated with mating success, particularly for low- and middle-ranking males. These results support the hypothesis that ageing male chimpanzees use coalitions as an alternative reproductive tactic. The lack of evidence for terminal investment in response to ageing appears to reflect a broader mammalian pattern in which males who rely on fighting to secure mating opportunities avoid excessive risk taking as their formidability wanes.

Parasites and infectious diseases constitute important challenges particularly for group-living animals. Social contact and shared space can both increase parasite transmission risk, while individual differences in social capital can help prevent infections. For example, high social status individuals and those with more or stronger affiliative partnerships may have better immunity and, thus, lower parasitic burden. To test for health trade-offs in the costs and benefits of sociality, we quantified how parasitic load varied with an individual's social status, as well as with their affiliative relationships with weakly and strongly bonded partners, in a free-ranging population of rhesus macaques, . We found that high status was associated with a lower risk of protozoa infection at older ages compared to younger and low-status animals. Social resources can also be protective against infection under environmentally challenging situations, such as natural disasters. Using cross-sectional data, we additionally examined the impact of a major hurricane on the sociality - parasite relationship in this system and found that the hurricane influenced the prevalence of specific parasites independent of sociality. Overall, our study adds to the growing evidence for social status as a strong predictor of infection risk and highlights how extreme environmental events could shape vulnerability and resistance to infection.

Motivation to seek social interactions is inherent to all social species. For instance, even with risk of disease transmission in a recent pandemic, humans sought out frequent in-person social interactions. In other social animals, socialization can be prioritized even over water or food consumption. Zebra finches, , are highly gregarious songbirds widely used in behavioural and physiological research. Songbirds, like humans, are vocal learners during development, which rely on intense auditory learning. Aside from supporting song learning, auditory learning further supports individual identification, mate choice and outcome associations in songbirds. To study auditory learning in a laboratory setting, studies often employ operant paradigms with food restriction and reinforcement and require complete social isolation, which can result in stress and other unintended physiological consequences for social species. Thus, in this work, we designed an operant behavioural method leveraging the sociality of zebra finches for goal-directed behaviours. Our approach relies on visual social reinforcement, without depriving the animals of food or social contact. Using this task, we found that visual social reinforcement was a strong motivational drive for operant behaviour. Motivation was sensitive to familiarity towards the stimulus animal and higher when engaging with a familiar versus a novel individual. We further show that this tool can be used to assess auditory discrimination learning using either songs or synthetic pure tones as stimuli. As birds gained experience in the task, they developed a strategy to maximize reward acquisition in spite of receiving more punishment, i.e. liberal response bias. Our operant paradigm provides an alternative to tasks using food reinforcement and could be applied to a variety of highly social species, such as rodents and nonhuman primates.

Population density is a fundamental ecological feature influencing the opportunity for social encounters between individuals. Hence, density can impact various population processes such as social transmission. While the density dependence of disease spread has been studied extensively, we know little about how variation in density influences information transmission. If high densities lead to more social connections, information may spread more rapidly. Here, we experimentally manipulated local population density in great tits, , and investigated the effects on individuals' acquisition of information on novel food patches. We manipulated density by assigning individuals to either a high- or low-density treatment using automated bird feeders in the wild. We first show how our approach successfully led to changes in local population density. Next, we examine how the manipulation changed the local and individual social environment. At the local level, high-density locations resulted on average in denser and more clustered social networks compared to low-density locations. At the individual level, birds assigned to the high-density treatment had on average more social connections and more central network positions than birds in the low-density treatment. However, despite the effect on network structure, we found no evidence that the density manipulation influenced an individuals' likelihood, or speed, of locating novel food patches. Birds in the low-density treatment still spent a large proportion of time foraging at the high-density location. Thus, the manipulation did not lead to a strict segregation between birds of the different treatments, which may be one explanation for the absence of an effect on patch discovery.

In cannibalistic species, conspecifics can be both predators and prey. As a result, conspecifics present a unique conflict at the intersection of predation, competition and nutritional resources in these species. To better understand how individuals respond to the complex information of conspecific chemical cues, we studied aggressive and cannibalistic tadpoles of the dyeing poison frog, . We used a standardized open field test to compare behavioural responses to a positive cue (food), a negative cue (predator) and two conflicting cues (conspecific density and injured conspecifics). We specifically used chemical cues to understand how individuals respond in the absence of additional information that would disambiguate their status as conspecific predator versus prey. We found that the injured conspecific cue elicited a response distinct from either the food cue or the predator cue: tadpoles explored more relative to baseline and predator cues but spent less time moving compared to the food cue. We suggest that these patterns reflect cue-dependent behavioural strategies that maximize exploration while minimizing detection in the presence of conspecific cannibals. In addition to cue-specific changes in behaviour, we observed consistent differences in individuals' behaviour across environments and found that activity and exploratory behaviour were positively correlated across environments. Taken together, our results demonstrate that conspecific cues are interpreted as distinct from either food cues or predator cues in a cannibalistic species where they can represent both.

Humans readily recognize familiar rhythmic patterns, such as isochrony (equal timing between events) across a wide range of rates. This reflects a facility with perceiving the relative timing of events, not just absolute interval durations. Several lines of evidence suggest this ability is supported by precise temporal predictions arising from forebrain auditory-motor interactions. We have shown previously that male zebra finches, , which possess specialized auditory-motor networks and communicate with rhythmically patterned sequences, share our ability to flexibly recognize isochrony across rates. To test the hypothesis that flexible rhythm pattern perception is linked to vocal learning, we ask whether female zebra finches, which do not learn to sing, can also recognize global temporal patterns. We find that females can flexibly recognize isochrony across a wide range of rates but perform slightly worse than males on average. These findings are consistent with recent work showing that while females have reduced forebrain song regions, the overall network connectivity of vocal premotor regions is similar to males and may support predictions of upcoming events. Comparative studies of male and female songbirds thus offer an opportunity to study how individual differences in auditory-motor connectivity influence perception of relative timing, a hallmark of human music perception.

Testosterone promotes mating effort, which involves intraspecific aggression for males of many species. Therefore, males with higher testosterone levels are often thought to be more aggressive. For mammals living in multimale groups, aggression is hypothesized to link male social status (i.e. dominance rank) and testosterone levels, given that high status predicts mating success and is acquired partly through aggressive intragroup competition. In male chimpanzees, , dominance rank has been repeatedly linked to interindividual variation in testosterone levels, but evidence directly linking interindividual variation in testosterone and aggression is lacking. In the present study, we test both aggression levels and lean muscle mass, as measured by urinary creatinine, as links between dominance rank and testosterone levels in a large sample of wild male chimpanzees. Multivariate analyses indicated that dominance rank was positively associated with total rates of intragroup aggression, average urinary testosterone levels and average urinary creatinine levels. Testosterone was positively associated with creatinine levels but negatively associated with total aggression rates. Furthermore, mediation analyses showed that testosterone levels facilitated an association between dominance rank and creatinine levels. Our results indicate that (1) adult male chimpanzees with higher average testosterone levels are often higher ranking but not more aggressive than males with lower testosterone and (2) lean muscle mass links dominance rank and testosterone levels in Ngogo males. We assert that aggression rates are insufficient to explain links between dominance rank and testosterone levels in male chimpanzees and that other social variables (e.g. male-male relationship quality) may regulate testosterone's links to aggression.

Machine-learning-based behavioural tracking is a rapidly growing method in the behavioural sciences providing data with high spatial and temporal resolution while reducing the risk of observer bias. Nevertheless, only a few canine behaviour studies have applied this method. In the current study, we used three-dimensional (3D) tracking of the dogs' bodies to study how separation from the caregiver affected the dogs' behaviour in a novel environment. During the study, the dogs could move freely in a room equipped with trial-unique objects. We manipulated across trials whether the owner and/or a stranger was present in the room to evaluate the secure base effect, the tendency to explore and play more in the presence of the caregiver compared to another person. This secure base effect is considered a key characteristic of human attachment bonds and has also been described for the dog-caregiver relationship. The tracking data were internally consistent and highly correlated with human scorings and measurements. The results show that both the owner and stranger significantly increased the dogs' exploration; the dogs also spent more time in the proximity of the owner and stranger location when they were present. Even though the presence of both owner and stranger had a significant effect on the dogs' behaviour, the effect of the owner was more pronounced. Moreover, in the presence of the stranger the dogs spent more time close to their owner and showed a reduced tail-wagging asymmetry to the right side further supporting the distinct effect of owner and stranger on the dogs' behaviour. We conclude that machine-driven 3D tracking provides an efficient and reliable access for detailed behavioural analyses of dogs' exploration and attachment-related behaviours.

Comparative studies of acoustic communication in clades with diverse signal features provide a powerful framework for testing relationships between perception and behaviour. We measured auditory sensitivity in five species of estrildid songbirds with acoustically distinct songs and tested whether differences aligned with species differences in song frequency content. Species were chosen based on phylogeny and differences in song acoustics. Behavioural audiograms were obtained using operant training and testing. Adult audiograms were compared across species and between sexes within a species. Juvenile and adult audiograms were compared in one species. The audiograms of adults reared by their own species and those reared and tutored by another species were compared in one species. Results showed that audiograms were similar across species and similar to previous reports of songbird auditory sensitivity. Species differed in the highest frequency detected and the frequency of peak sensitivity. While hearing frequency range was not correlated with song frequency bandwidth, the frequency of peak sensitivity was highly corelated with the frequency of peak energy in song. Sensitivity did not differ based on sex, age or tutoring experience. Our findings suggest that adaptations in songbird auditory sensitivity are largely constrained by shared peripheral and central encoding mechanisms, with species-specific perception appearing only at peak sensitivity.

Primates of several species respond negatively to receiving less preferred rewards than a partner for completing the same task (inequity responses), either rejecting rewards or refusing to participate in the task when disadvantaged. This has been linked to cooperation, with species that cooperate frequently refusing to participate in inequity tasks (the 'cooperation hypothesis'). However, inequity is a social response, and previous research has involved dyads, precluding studying the effects of additional social partners. While dyads allow for tighter control in experimental settings, dyadic interactions in nature do not take place in a social vacuum, so understanding the role of the social context is needed to verify that the pattern of results supports the cooperation hypothesis. Here we focus on Bolivian squirrel monkeys, , a highly social species that does not generally cooperate and has not responded to inequity in previous dyadic research, although they do respond to receiving a lower reward than they expected. In the current study, we provide a more nuanced test by studying female Bolivian squirrel monkeys, the demographic most likely to cooperate in both field and laboratory contexts, in a more socially relevant group setting. For some reward values, females responded in both the inequity condition, rejecting less preferred rewards when they were disadvantaged relative to their social group, and a contrast condition, wherein all animals received a lower reward than they expected, making it difficult to disentangle contrast from inequity. As in capuchin monkeys, refusals increased when monkeys were to receive low-value rewards compared to medium-value rewards. These results suggest that the relationship between cooperation and inequity responses may be more nuanced than previously suggested, with demographic, social context and reward value potentially influencing outcomes even within species.

As Darwin first recognized, the study of emotional communication has the potential to improve scientific understanding of the mechanisms of signal production as well as how signals evolve. We examined the relationships between emotional arousal and selected acoustic characteristics of coo and scream vocalizations produced by female rhesus macaques, , during development. For coos, arousal was assessed through measures of stress-induced elevations of plasma cortisol exhibited in response to the human intruder test. In the analysis of screams, arousal was evaluated from the intensity of aggression experienced by the vocalizer during natural social interactions. Both call types showed a positive relationship between arousal and overall fundamental frequency (F0, perceived as pitch in humans). In coos, this association was dampened over development from infancy (6 months) to the juvenile, prepubertal period (16 months) and further to menarche (21.3-31.3 months), perhaps reflecting developmental changes in physiology, anatomy and/or call function. Heightened arousal was also associated in coos with increases in an acoustic dimension related to F0 modulation and noisiness. As monkeys matured, coos showed decreases in overall F0 as well as increased noisiness and F0 modulation, likely reflecting growth of the vocal apparatus and changes in vocal fold oscillation. Within screams, only one acoustic dimension (related to F0 modulation) showed developmental change, and only within one subclass of screams within one behavioural context. Our results regarding the acoustic correlates of arousal in both call types are broadly consistent with findings in other species, supporting the hypothesis of evolutionary continuity in emotion expression. We discuss implications for broader theories of how vocal acoustics respond to selection pressures.

It has recently been found that iridescence, a taxonomically widespread form of animal coloration defined by a change in hue with viewing angle, can act as a highly effective form of camouflage. However, little is known about whether iridescence can confer a survival benefit to prey postdetection and, if so, which optical properties of iridescent prey are important for this putative protective function. Here, we tested the effects of both iridescence and surface gloss (i.e. specular reflection) on the attack behaviour of prey-naïve avian predators. Using real and artificial jewel beetle, , wing cases, we found that iridescence provides initial protection against avian predation by significantly reducing the willingness to attack. Importantly, we found that the main factor explaining this aversion is iridescence, not multiple colours per se, with surface gloss also having an independent effect. Our results are important because they demonstrate that even when prey are presented up close and against a mismatching background, iridescence may confer a survival benefit by inducing hesitation or even, as sometimes observed, an aversion response in attacking birds. Furthermore, this means that even postdetection, prey do not necessarily need to have secondary defences such as sharp spines or toxins for iridescence to have a protective effect. Taken together, our results suggest that reduced avian predation could facilitate the initial evolution of iridescence in many species of insects and that it is the defining feature of iridescence, its colour changeability, that is important for this effect.

Investigating the impact of parasitism on host phenotype is key to understanding parasite transmission ecology, host behavioural ecology and host-parasite coevolution. Previous studies have provided evidence that avian odour is one such phenotypic trait, as mosquitoes that vector the haemosporidian blood parasite tend to prefer birds that are already infected. Preen oil is a major source of avian odour, yet studies to date have not identified differences in preen oil odour based on the presence or absence of haemosporidian infection. Because preen oil can vary with physiological dynamics, we predicted that the composition of preen oil odours might vary according to parasite load, rather than solely by the presence or absence of infection. We used gas chromatography-mass spectrometry to characterize the composition of volatile compounds in preen oil taken from female dark-eyed juncos, and asked whether their composition varied with relative haemosporidian parasite load, which we assessed using quantitative PCR. We identified a subset of volatile compounds (a 'blend') and two specific compounds that varied with increasing parasite load. Importantly, the quantity of these compounds did not vary based on parasite presence or absence, suggesting that birds with low parasite loads might be phenotypically indistinguishable from uninfected birds. The volatile blend associated with parasite load also varied with sampling date, suggesting a possible seasonal relapse of chronic infections triggered by shifts in junco host reproductive state. Furthermore, we found a positive relationship between parasite load and a volatile blend shown in a previous study to predict reproductive success in juncos. This is the first study to demonstrate quantitative differences in avian host odour based on haemosporidian parasite load. Our findings highlight the importance of focusing on parasite load, rather than solely presence or absence, in investigating host-parasite interactions.

Pathogen virulence is highly variable within populations, and although many factors contributing to virulence differences are known, there is still much variation left unexplained. Identifying and characterizing environmental conditions associated with different virulence levels is therefore an important undertaking in infectious disease research. One factor considered to be a major determinant of overall health and susceptibility to disease in social animals is social status. Health differences associated with social status are thought to be caused by different levels of chronic stress in higher- versus lower-status individuals. There is considerable evidence that these effects extend to the standing immune profile and that social status directly influences susceptibility to pathogens. Here we examined the association between dominance status in male wild-derived house mice, , and susceptibility to Friend virus complex in the context of seminatural populations with intense male-male competition and no predation. Due to an interruption in our facility's heating system, we were unexpectedly presented with the opportunity to assess how reduced ambient temperature influences the association of host social status and pathogen virulence. Environmental temperature has been implicated as a contributor to pathogen virulence, giving us a unique chance to examine its role in a previously unexamined pathogen system, while the added context of social status can expand our understanding of how the interaction of different environmental conditions affects virulence. We found that pathogen virulence and replication were lower in socially dominant hosts compared to nondominant hosts. When temperature was reduced, cool enclosure-housed dominant males were more susceptible to infection than their warm enclosure-housed counterparts. The mechanistic underpinnings that link infectious disease and social status remain difficult to disentangle from their associated factors, but this study opens the door for future experiments using a novel approach in the most well-studied mammalian model available.

Emotional contagion refers to the mechanism of aligning with conspecifics' emotional states and is thought to be highly beneficial in social group living. While emotional contagion is well studied in humans, most studies in nonhuman animals fail to clearly distinguish between behavioural and emotional contagion. Furthermore, evidence for positive emotional contagion in nonhuman animals is almost entirely restricted to the context of play. In the present study, we aimed at adding observational evidence of contagion in a positive context, while separating aspects of behavioural and emotional contagion. In a group of nonbreeder common ravens, , we investigated whether witnessing conspecifics in positive social interaction, namely allopreening, would influence a bystander's behavioural and, possibly, emotional state. We recorded behavioural expressions of bystanders in postpreening observation phases and compared them to those in matched-control observation phases. We found effects of witnessing others' allopreening on the bystanders' subsequent affiliative interactions but not on their self-directed behaviours (e.g. autopreening) or agonistic interactions. Specifically, bystanders were more likely to engage in allopreening themselves in the postpreening observation phase than in the matched-control observation phase, which could be explained via behavioural and emotional contagion; however, bystanders also showed elevated levels of nonpreening affiliative interactions and spent more time close to conspecifics after observing others allopreening, which hints towards a more general effect on the bystanders' emotional states. Whether these nonpreening affiliative interactions are indeed an indication of emotional contagion needs to be tested in further studies that measure, and manipulate, emotional states.