An investigation of playful behaviour in Rattus norvegicus and Mus musculus (Mammalia)

The playful behaviour of laboratory rats ( Rattus norvegicus ) was investigated in litters of five individuals with the mother present; parallel observations were made on mice ( Mus musculus ). Seven mixed litters containing four young rats and a young mouse fostered at birth were also observed.
Solitary play was recorded in both species and took a similar form but social play was only observed in rats. In rats, solitary play frequently preceeded social play.
The behavioural elements involved in the social play of Rattus norvegicus were described, and the majority of these were the playful equivalent of adult agonistic behaviour elements. These social play elements were found to be organized into definite sequences which differed from those of adult aggression. Each behavioural element was found to act as a social releaser.
Young mice did not respond playfully to social play from a rat litter mate; mice were less attractive to rats as playmates in comparison with fellow rats.     

Development of Social Behaviour in Four Litters of Dogs (Canis familiaris)

The development of social behaviour in 4 litters of dogs was observed without interfering with the puppies from birth to 8 weeks of age. Direct and continuous observation was combined with video recording. Three of the litters were observed during one session of 2 h once a week, and the fourth litter during one session of 40 min twice a week. Social interactions were divided into 1) investigation of litter mates (licking, sniffing or investigating orally), 2) social play, 3) and interactions in which agonistic elements (dominance postures, threats, bites or submission) were displayed. The different forms of social interactions appeared for the first time when the puppies were between 14 and 21 days of age. Social investigation appeared first and was followed by play and agonistic interactions. From week 5, differences between the puppies in the tendency to initiate social play and agonistic interactions emerged. Generally, within the litters individual differences were consistent over weeks 6-8 (positive correlations between weeks), whereas the tendency in the puppies during these weeks were negatively correlated with those of week 3 (play) or weeks 3 and 4 (agonistic interactions), indicating a rebound effect for both play and agonistic behaviour. No significant correlations, however, were found for social investigation. More often than expected males played or engaged in agonistic with other males, whereas these behaviours occurred less often than expected between females. Both males and females, however, preferred male partners for agonistic interactions. No sex differences were found in the direction of social investigation. Agonistic behaviour was often responded to by play and play was often responded to by agonistic behaviour, and the results indicated that before 8 weeks of age differences in social behaviour between the puppies were already established.     

Precocious Courtship and Play in Emydid Turtles

In many mammal species, precocious sexual behaviour is a component of play. A recent model for the evolution of play fighting behaviour in muroid rodents by Pellis (1993) proposes that social play in those species has its origin in precocious sexual behaviour. Captive juvenile emydid turtles perform precocious sexual behaviour. After reviewing its occurrence, we focus on detailed observations of Pseudemys nelsoni. Precocious sexual behaviour in these turtles is characterized by the striking ‘titillation’ display, usually observed only when adult males court females. In this display, the digits of the front feet are rapidly vibrated above the eyes of the female. In our observations, both sexes performed the display, which was energetic, spontaneous, and inconclusive (in that sequences of precocious courtship typically ended when either the displayer or recipient stopped and rested, left, or started some other unrelated non-social behaviour). Displaying individuals clearly preferred conspecific recipients and often appeared to seek out specific individuals. We discuss several plausible explanations for precocious courtship in these turtles but find none entirely satisfying. The characteristics of the precocious courtship behaviour we observed most closely match those commonly listed for social play. Thus, we conclude that the most likely explanation for this behaviour is that it is a component of social play.     

Play behaviour in lowland gorillas: Age differences,sex differences,and possible functions

A study on lowland gorilla (Gorilla gorilla gorilla) play behaviour was conducted on four exhibits at three different zoological parks so that 19 gorillas were observed. Juvenile gorillas played the most, but play continued at fairly high frequencies through adolescence. Most social play occurred between dyads. Triadic groups usually chased each other. No sex differences in type of play were observed, but gender differences in partner preferences were observed. Males played with both other males and females, while females seldom played together. These data support the social skills hypothesis (Baldwin & Baldwin, 1974) of play. Data were gathered while the author was a graduate student at Tulane University and a visiting lecturer at the University of California, Riverside.     

Play behaviour and its effects on social development of common chimpanzees (Pan troglodytes)

The aim of the study was to monitor the social development of infant and juvenile common chimpanzees (Pan troglodytes) through their play behaviour at Taronga Zoo in Sydney in order to examine the possible effects of captivity (such as limited opportunities to play) on social development. Play behaviour was observed by focal animal sampling to determine individual differences, and their relationship to age, sex, and relatedness of the subjects. Analysis revealed marked individual variations in social, solitary, and object play behaviours indicative of a relatively well-balanced social and physical environment. Subjects showed a marked preference for play-partners of a different age compared to their own, and initiated interactions with similar frequency with members of both sexes. Many social-play dyads consisted of related individuals, and familiarity with prospective play-mates was the most decisive factor in social interactions.     

Sex differences in the behaviour of immature captive lowland gorillas

Studies of the behaviour of 26 (12 males and 14 females) captive infant and juvenile lowland gorillas showed clear sex differences. Females showed greater interest in young infants and were more active in nest building as well as in solitary and social grooming. Males were more active in locomotive, dominance, and aggressive behaviour and in social play. Hand-rearing further increased aggression. Males were more aggressive when they lived with only one partner, and they rose in rank even above older females, a pattern that has not been observed in naturally reared gorillas.     

Social interactions of juvenile Collared peccaries, Tayassu tajacu (Mammalia: Artiodactyla)

Is there a predictable relationship between species-typical behavioural development and social organization in mammals? Earlier work on canids and rodents suggested that adult sociality is associated with a developmental schedule in which juveniles showed, among themselves: (1) frequent social play; (2) frequent amicable contact; (3) frequent olfactory contact; (4) a delay in the emergence of agonistic behaviour. In the highly social Collared peccary (Tayassu tajacu) the behaviour of juveniles conformed only partially to this scheme. Juveniles engaged in social play with each other at an early age, but showed no other observable amicable or olfactory contact until eight to twelve weeks of age and showed no delay in the emergence of agonistic behaviour among themselves. Adults, in contrast, were conspicuously tolerant of juveniles, and 86% of juvenile social interactions in the first year took place with adults.     

Functions and consequences of play behaviour in juvenile Belding's ground squirrels

We evaluated hypotheses suggesting that play behaviour in free-living juvenile Belding's ground squirrels, Spermophilus beldingi, helps to regulate energy balance and promotes development of motor skills. We also examined the possibility that play behaviour and motor development influence important early life events in S. beldingi. We regularly measured body fat of juveniles using nondestructive methods, observed their behaviour, conducted motor skills tests, monitored dispersal status of males, and evaluated weaning success of females during their first effort to reproduce as yearlings. Rates of feeding were greater among juveniles who engaged in both social and nonsocial play behaviour at low compared to high rates, suggesting that play does not help young animals expend excess energy that they consume. By contrast, body fat was greater among juveniles who engaged in social play at high compared to low rates, supporting the idea that energetic variables such as body fat limit the expression of play behaviour. Motor skills of juvenile S. beldingi improved throughout the period in which juveniles engaged in play behaviour. Improvement in motor skills was greater in juveniles who engaged in social play at high compared to low rates, suggesting a link between social play and motor development. Motor skill levels at the end of the play period were greater among males who dispersed by the end of the juvenile summer than among males still residing in their natal areas. Rates of social play and improvement in motor skills over the course of the play period were greater in females who successfully weaned a litter as yearling than in females who did not. These last two results raise the possibility that play behaviour and motor development during the play period influence important events in the early lives of S. beldingi, which may ultimately influence long-term reproductive success.     

Differential Behavioural Effects of Silent Bared Teeth Display and Relaxed Open Mouth Display in Chimpanzees (Pan troglodytes)

This study examines the behavioural consequences of the silent bared teeth display (SBT) and the relaxed open mouth display (ROM) in the chimpanzee, and discusses functional similarities with smiling and laughing (respectively) in humans. Rates of affinitive behaviour increase (in relation to baseline levels) following SBT, suggesting that SBT is a signal of affinity. ROM is observed primarily during play, and dyadic play bouts are significantly longer when ROM is bidirectional, indicating that it may be a signal of play. Rates of affinitive behaviour also increased after ROM, suggesting that both displays may have a similar ultimate (evolutionary) function – social bonding; this could explain convergence of the two displays in humans.     

Homosexual behaviour and female-male mounting in mammals—a first survey

Information from the literature is given on the presence or absence of homosexual behaviour and female-male mounting in 125 species of mammals, both captive and wild. Such behaviour occurs in the male and often female young of many species soon after their birth. It is more common in young, often in play, than in adults. Adult homosexual behaviour is widespread in male and female mammals (recorded in 63 and 71 species respectively), but common in few species. In males it is most likely to be correlated with dominance and thus to occur in species with hierarchies such as terrestrial monkeys and members of the sheep and goat tribe. In females it is often correlated with sexual condition; a female in heat most often mounted another female, and one in heat was next most likely to be mounted by another female. Anoestral females rarely mounted other anoestral females. Females of 43 species mounted males, which often excited them sexually. Captive mammals tended to mount animals of the same sex more often than did wild ones when comparative data were available. Domestic animals also mounted more man did wild ones, with several exceptions. Some phylogenetic groups of animals displayed similar degrees of homosexual mounting, but there was often considerable variation between closely related species. Nor could homosexual mounting be always correlated with the social structure of a group. The four reasons for, or contexts of, homosexual and female-male mountings were social play (in 34 species), aggression (19 species), sexual excitement (36 species), and physical contact—non-play (30 species). This last category included a state of tension, getting attention, greeting, grooming, caressing, reassurance and appeasement. There was some overlap between categories. Homosexual pair-bonds occur in captive mammals and have been observed throughout the year in non-captive female Japanese monkeys.     

Ontogeny of Dominance in Free-living Red Foxes

We established the ethogram of fox pups of free-living foxes after emergence from the den. We recorded the reactions of the pups during encounters to determine their social status and documented the relationship between social status and social play. The ethogram comprised 12 behavioural classes including 64 behavioural acts. ‘Moving’ and ‘exploration’ were the most observed classes with a frequency of occurrence higher than 20%. Most behavioural acts occurred at frequencies ranging from 0.5% to 5%. The intra-litter hierarchy was linear. Social play was the predominant type of social activity among pups, and induced the maintenance of dominance relationships among them. Adult—juvenile interactions (‘relation with an adult’ and ‘suckling’) could depend on the social rank of the juveniles. Juvenile-juvenile contacts allowing strong social bonds to develop between littermates (‘tactile communication’ and ‘comfort social behaviour licking and nibbling fur’) were not correlated with the social rank of the juveniles.     

Quantitative studies of behaviour within captive groups of marmoset monkeys (Callithrix jacchus)

Quantitative data were collected on the behaviour of four social groupings of captive common marmost monkeys. The observational study covered a period of eight months in 1973 during which time, data were intermittently collected on marking, self and social grooming, three categories of social play, together with some few additional data on close physical proximity and social contact referred to as ‘huddling.’ Each social group was observed for a total of 180-ten-min. observation sessions; one family group of monkeys was further observed individually for 100-ten-min. sessions.     

Control of the change from group to pair behaviour by Hodotermes mossambicus reproductives

Groups of Hodotermes mossambicus reproductives exhibit social behaviour. Maintenance of this behaviour by an individual depends on frequent contact of its body by the antennae of other termites. The antennae of the recipient do not play a rôle. Pairs on the other hand exhibit antisocial behaviour. Development of pair behaviour occurs when antenna to body contact is reduced or absent. Furthermore, at least the proximal parts of the antennae are required for full development of pair behaviour. Pheromones are not implicated in the change from group to pair behaviour.     

Promoting positive states: the effect of early human handling on play and exploratory behaviour in pigs

It is known that tactile stimulation (TS) during ontogeny modifies brain plasticity and enhances the motor and cognitive skills. Our hypothesis was that early handling including TS would increase play and exploratory behaviour in commercial pigs under standardized test conditions. Piglets from 13 litters were subjected to three handling treatments from 5 to 35 days of age: all the piglets were handled (H), none of the piglets were handled (NH) or half of the piglets in the litter were handled (50/50). At 42 days of age, the pigs’ behaviour was observed in pairs in a novel pen with a ‘toy’ (tug rope). The main results were that more locomotor play was performed by pigs from litters where all or half of them had been handled, whereas social exploratory behaviour was more pronounced in pigs from litters where half of them had been handled. Although behaviour was affected by the interaction of treatment with sex or with weight category, we propose that the handling procedure does seem to have acted to increase locomotor skills and that handling half of the piglets in the litter may have triggered a series of socio-emotional interactions that were beneficial for the whole group.     

The Development of Play in the South American Fur Seal

Play behaviour in the juvenile South American fur seal (Arctocephalus australis) is described for the period of dependence on the mother (up to 32 months). Play does not appear to be a unitary category of behaviour, but may be separated into four distinct types: terrestrial social and solitary play and swimming social and solitary play. These four types show different development profiles, and appear to serve different functions. Terrestrial solitary play and the two swimming play forms appear to be juvenile specializations, the first to enable very young seals to gain motor skills rapidly in order to avoid dangers from conspecifics, the second two to enhance antipredator behaviour and foraging ability during the gradual transition to independence. In contrast, social play may be best thought of as gaining social skills necessary in adult life, prior to dispersal post-weaning. Juvenile fur seals which do not wean in their first year show an upsurge in social play which is not seen in the other play types. This upsurge coincides temporally with the peak of social play of the new cohort, and is presumably elicited by them.     

Association behaviour of the self-fertilizing Kryptolebias marmoratus (Poey): the influence of microhabitat use on the potential for a complex mating system

Preliminary observations were conducted to identify conspicuous body postures and movements of males and hermaphrodites in the mangrove killifish Kryptolebias marmoratus . These behaviours were used quantitatively to examine the social interactions for experimental pairings of K. marmoratus of different sexual states ( i.e. simultaneous hermaphrodite and male) in an aquarium with an open-water area and simulated crab burrows. This allowed observation of behaviours that could not be observed in the field. Kryptolebias marmoratus , regardless of sexual state and experimental treatment, spent 40% of the time in the burrow. Hermaphrodites exhibited a preference for associating with males rather than other hermaphrodites. The observed complexity of displayed behaviours and interactions between paired conspecifics indicate that K. marmoratus has a rich repertoire of social behaviour not predicted for a strictly selfing species. Also, land crab burrows play an important role in their social interactions.     

A descriptive study of social development in the rat (Rattus norvegicus)

The social interactions between juvenile rat pups (Rattus norvegicus) were observed daily between 21 and 55 days of age. The data were analysed for developmental changes, sex differences, play-partner preferences, and dominance relations. The results revealed clear patterns in the development of sexual and agonistic behaviours in the rat. This development refers to changes in either the manner in which animals interact or the behaviours involved in social play, but not to the topography of specific behaviours. Development toward the adult pattern of social behaviour was temporally associated with the period of sexual maturation (i.e. between days 36 and 50).     

Das Spielverhalten der Keas (Nestor notabilis Gould) des Zürcher Zoos

This study uses a new definition of play behaviour to find out play sequences and the elements the kea uses during play. 14 different keas (2 pairs with 3 and 4 chicks and 3 adults) were observed during 420 h. Observations were made by filming (16 mm), photographing and by speaking sequences on tape-recorder. The observations showed that it was almost always possible to separate play sequences from other behaviour. Some difficulties arose because the behaviour sequences of the kea have a high percentage of variance. To prove that the definition of play is really useful one should use a species whose behaviour is largely innate and not as adaptive as in the kea. With such a species the sequences of “normal” behaviour would be well defined, while the sequences of play behaviour should show no order.     

An investigation of individual, age and sexual differences in the play of Rattus norvegicus (Mammalia: Rodentia)

Eight litters of Rattus norvegicus of the PVG/C hooded strain were observed in order to investigate the roles of individuality, sexuality and age in playful behaviour.
Three measures of social play, namely, initiations, numbers of play bouts and numbers of playful elements performed were all found to be positively correlated. The incidence of social and solitary play were also positively correlated so that a concept of "playfulness" appeared to be justifiable. Playfulness showed no correlation with the general level of non-playful locomotor activity.
Male rats were more playful than females but only minor sex-related differences were found to occur in the sequential organisation of play.
Older rats showed longer play bouts and a higher degree of temporal organisation. Considerable individual differences in playfulness were recorded and in single sex litters playful rats were found to play together.
The majority of opponents, in playfighting, alternated between the roles of attacker and defender.     

The effects of litter-size variation on the development of play behaviour in the domestic cat: litters of one and two

In many litter-bearing species, litter-mates interact with each other in a variety of ways during early life. In the domestic cat, Felis catus, social play is a prominent form of interaction between litter-mates. The present study investigated how the lack of a litter-mate affected the development of kitten play and of the mother-kitten relationship. The subjects were 14 litters of domestic kittens living with their mothers in large indoor cages. Seven litters contained two male kittens, and the other seven contained single male kittens. Social interactions within the families were observed from day 22 to day 83 after birth. Single kittens played a more active part in maintaining close proximity to their mothers and directed more playful behaviour at them than did kittens with a sibling. Although single-kitten mothers avoided their offspring more than did mothers of litters of two, they also directed much higher levels of play behaviour at them. Despite the marked difference in the mother-kitten play relationship in the two litter types, single kittens experienced quantitatively less social play than did kittens with siblings. As the kittens grew older, single-kitten mothers showed higher levels of aggression towards their young than did mothers of litters of two.