Interspecific social behaviour in animals refers to social interactions between individuals belonging to different species. Such interactions range from brief encounters around food to prolonged relationships involving grooming, play, protection, caregiving and other behaviours normally directed towards members of the same species.
Interspecific interactions occur in many animal groups. They may arise because the animals obtain a clear adaptive benefit from their association (food or protection), but some relationships appear to involve only social or affiliative behaviours with little obvious adaptive benefit. Particularly striking examples have been documented among non-human primates, including cases in which they repeatedly groom, play with, carry or care for individuals of other species.
Some of these relationships have been compared with human-animal companionship or pet-keeping. However, whether animals can be said to “keep pets” in the human sense remains uncertain. Researchers generally confine themselves to the observation of interspecific affiliation without attempting to attribute a specific motivation or intent to the animals involved.
Primates
Non-human primates provide some of the best-documented examples of interspecific social behaviour. Primates possess sophisticated social systems and, within these systems, they regularly engage in grooming, play, coalition formation and infant care. Field research has shown that these behavioral patterns are occasionally directed towards members of another species.
A peer reviewed 2026 article on interspecific interactions by Cyril C. Grueter et al. used information from scientific papers, media reports and a survey of 37 primatologists. Using this database, the authors compiled 427 cases of interspecific interactions involving at least one primate species — specifically, the interaction involved 88 primate species and 127 species of other animals. The primates’ interactions were with other primates as well as with other mammals, birds, reptiles, amphibians, crustaceans and insects. Play and grooming were the most frequently reported behaviours. The interactions occurred both in the wild and in captivity.
Patterns emerged in how the primates interacted with other species based on their age and sex. Juvenile primates were more likely to engage in play, while females were more likely to groom. Adult females were the most likely to engage in such interspecific behaviors, followed by juveniles. Adult males were the least likely to engage in Interspecific interactions. The vast majority of the interactions with non-primates were initiated by the primates (only 3 percent were initiated by non primates).
More generally, the authors note that interspecific interactions “often involve the ability to read and respond appropriately to the social cues of other species that are sometimes taxonomically distant, highlighting important links between perception, communication, and social cognition.”
Overview of interactions Interspecific social behaviour encompasses several types of interaction. Animals of different species may associate repeatedly because their activities provide mutual or one-sided benefits. For example, different species may travel or forage together. These polyspecific associations can provide advantages such as increased vigilance against predators, access to food or improved opportunities to detect threats. They do not necessarily imply that the animals form individual social bonds.
The three types of social interaction reported most frequently in the 2026 article were:
Grooming: In many primate species, grooming strengthens relationships, reduces tension and can provide information about social status. Grooming between species has been observed in a number of animals, particularly primates. Because grooming is often strongly associated with affiliation within a species, repeated grooming between individuals of different species can be evidence of an unusually close relationship. Nevertheless, grooming may also have hygienic functions. Play: Animals sometimes play with members of another species. Among primates, such behaviour is particularly common in young animals and may include chasing, wrestling, object manipulation and other activities.. Play requires communication between the play partners and, because of communication barriers between species, most species only play with conspecifics. In contrast, interspecific play “involves reading and responding appropriately to social cues of other species, often taxonomically remote, and has implications for perception, communication, and cognition.” Thus, interspecific play requires a convergence of enabling conditions, including physical proximity and ability of each play partner to understand the other’s play signals. Adoptive behaviour and alloparenting: An adult may carry, protect or otherwise care for an unrelated young animal. Such behaviour is sometimes described as interspecific adoption or alloparenting. It may result from the extension of normal parental or alloparental responses to an individual of another species. Whether the caregiver has formed a lasting social bond with the adopted animal, rather than simply responding to its infantile characteristics, is often difficult to determine. The observations in the 2026 article show that alloparenting behavior occasionally resulted in the infant’s death, through “rough handling or disregard.”
Examples
Chimpanzees grooming and playing with smaller primates Wild chimpanzees in Gombe Stream National Park have been observed engaging in interspecies play with olive baboons. Young chimpanzees and juvenile olive baboons share overlapping habitats and participate in similar social actions such as chasing, wrestling, and mutual grasping. Researchers from the Jane Goodall Institute have captured footage of specific interactions, such as an infant chimpanzee playing with a young olive baboon. Beyond play, Gombe's chimpanzees have occasionally been observed grooming, and occasionally, even attempting to woo primate species different from their own.
Wild chimpanzees in Uganda's Budongo Forest Reserve have been observed grooming and playing with members of local monkey species they normally hunt as prey. From 1993 to 2021, researchers have documented six interspecific grooming events and one play event. The groomers were young female chimpanzees aged 4 to 6 years old. The recipients of grooming were most frequently red-tailed monkeys and occasionally blue monkeys (often adult males). The play event involved three juvenile male chimpanzees and a red-tailed monkey. The exact purpose of these behaviours is unclear, though researchers suggest it may serve as social or grooming practice for young chimpanzees.
Capuchins raising infant marmosets Researchers in Brazil observed a group of black capuchins caring for and raising an infant common marmoset. The marmoset was carried and interacted with by members of the capuchin group over. It lived, traveled and integrated with the capuchin troop for about 14 months. The capuchins’ nurturing behaviour resembled the carrying and social care normally provide to infants of their own species. This observation is significant because it involved prolonged social and caregiving behaviour rather than a single encounter.
Macaques riding sika deer Using video data from two sites, Yakushima Island and Minoh, Japan, 45 macaque–sika deer mounting interactions (that is, the macaque rides on the back of the deer) were identified. These were classified into four primary activities performed by macaques during mounting: sexual, play, grooming, and resting, with resting being the most common. Another article reported attempted mating behaviour between a male Japanese macaque and female sika deer on Yakushima Island. This individual showed unambiguous sexual behaviour towards several female deer, some of which tried to escape whilst others accepted the mount. The authors believe that this behavior might be due to mate deprivation.
Capuchin monkeys kidnapping infant howler monkeys A May 2025 paper documents the first known observation of wild monkeys passing down a non-adaptive "fad" involving the abduction of infants from another species in Jicarón Island in Coiba National Park, Panama. Five adolescent male white-faced capuchin monkeys (Cebus capucinus imitator) carried 11 unique infant howler monkeys (Alouatta palliata coibensis) over a 15-month period (January 2022 to July 2023). The behavior started with a single subadult male in January 2022 and had spread to four other juvenile and subadult males by September 2022. The abducted howler infants suffered severe malnourishment and at least four of them died. Indeed, it is not unusual for interspecific interactions to result in injury or death for one of the animals involved. Researchers also noted that the carrying behavior provided no clear food acquisition or other fitness benefit.
Monkeys and domestic animals Other observations involve primates and domesticated animals. Monkeys have been observed grooming, playing with and interacting with dogs, pigs and other domestic animals. The 2026 review reported examples including stump-tailed macaques grooming domestic dogs in Thailand and black-and-white snub-nosed monkeys playing with domestic pigs in China.
Scientific understanding of interspecific social relations Interspecific social behaviour is difficult to study systematically because such interactions are relatively rare and may be reported selectively. Some primate species have been studied intensively for decades, while others have hardly been studied at all. Furthermore, the researchers making the observations were not generally following a research protocol tailored to interspecific social interaction. Observations occurred only when researchers happened to see such interactions and their reports are “brief and anecdotal.” Thus, the current collection of observations is idiosyncratic; it is based on somewhat random field observations as well as on casual observations posted on social media. Future research using more systematic observations may help shed light on how frequently animals form lasting relationships with members of other species and what functions these relationships serve.
For now, researchers have identified a number of factors that may contribute to the formation of interspecific social relationships:
Shared social tendencies: Closely related species often possess similar behavioral repertoires. Individuals from two species that engage in grooming, play or infant carrying may therefore respond to one another in socially appropriate ways despite belonging to different species. This mutual compatibility may be particularly important among primates, whose social cognition and communication systems are relatively complex. Juvenile behaviour: Young animals, relative to their elders, are more likely to explore and play with individuals outside their own species. Learning parenting skills: Play is necessary for individual development in many species, including primates. The ‘learning to mother’ hypothesis proposes that play that involves interactions with infants allows juveniles, especially females, to acquire parenting skills. This hypothesis might be relevant for interspecies play involving infant primates, though data is not yet sufficient to draw conclusions. Misidentification or generalized caregiving: Parental behaviour may be triggered by characteristics associated with infancy rather than by species identity. In primates, a common signal is differences in facial and coat colors between infants and adults. According to this theory, an adult may care for an infant belonging to another species because it resembles an infant of its own species. The 2026 review of primate interactions does not provide evidence that this is an important consideration in such interactions.