Aggression with mixed age-sex groups of bolivian squirrel monkeys following single animal introductions and new group formations

The social organization of the Bolivian squirrel monkey (Saimiri boliviensis boliviensis) is thought to be sexually segregated, with males and females forming separate social groups during the nonbreeding season. To investigate the influence of this social order on patterns of aggression, controlled single animal introductions within established groups and establishment of new groups were studied in a systematic manner. Behavioral observations were made using an all-occurrences technique to sample all agonistic interactions. In study I, 4 animals of each age-sex class (adult males and females, juvenile males and females) were introduced one at a time into 4 different social groups composed of 1 adult male and 8 to 10 adult females. Behavioral observations were made prior to and after the introductions. Newly introduced adult males received significantly more contact aggression than other age classes. Only the adult females increased aggression after the introduction of new animals. In study II, new social groups were formed and behavioral observations were made following formation. One group was formed from 7 pairs of familiar females and an unfamiliar adult male. This group had a high frequency of aggression during the first half hour, with contact aggression rising to peaks at 3 and 5 h. The second group consisted of 10 familiar females, 2 pairs of familiar females and an unfamiliar male. There was a significant peak in contact aggression 3 h into the observation.     

Social facilitation of agonistic responses to strangers in pairs of saddle back tamarins (Saguinus fuscicollis)

The effect of the presence of a familiar social partner on the interactions of saddle back tamarins with unfamiliar conspecifics was studied. Fifteen adult male-female pairs, of which six were composed of a castrated male and an intact female, served as subjects. All subject pairs were given two social encounters during which both mates met a strange male and two encounters during which they met a strange female. In addition, all subjects were given four encounters during which they met the same strangers while their own pair mates were absent. As a group, the subjects showed higher intensities of injurious aggression and of agonistic displays when they met strangers in the presence of their own pair mates. Females and castrated males, as subgroups, showed significant increases in most agonistic responses when they met strangers in the presence of their pair mates. Intact males, however, did not.     

The effect of familiarity on social interactions in meadow voles,Microtus pennsylvanicus: a laboratory and field study

The role of familiarity in affecting the outcome of social interactions among meadow voles was investigated in both a laboratory and a field experiment. In the laboratory, captive meadow voles, Microtus pennsylvanicus, were exposed to a conspecific's odour. The voles were then placed into two groups: familiar and unfamiliar. Familiar voles were individuals who underwent staged dyadic encounters with the conspecific to whose odours they had been exposed. Unfamiliar voles were individuals who underwent paired encounters with conspecifics to whose odours they had not been exposed. In the field experiment, familiar voles were neighbours that were trapped within each other's home ranges over two consecutive bi-weekly trapping sessions. Unfamiliar voles were individuals that were trapped on different trapping grids. The results of the laboratory and field studies were similar. Encounters between familiar females resulted in less agonistic behaviour and more amicable acts than encounters between unfamiliar females. In contrast, encounters between familiar males resulted in more agonistic behaviour than encounters between unfamiliar males. Familiarity did not affect the outcome of male-female interactions. These results are discussed in the framework of the social system of the meadow vole.     

The effects of familiarity on competitive interactions between threespined sticklebacks

In this study, pairs of juvenile sticklebacks either familiar with each other or pairs unfamiliar with each other met to share a food source. The study showed that sticklebacks were less aggressive towards a partner when sharing a common food source with a familiar conspecific, compared to when sharing a food source with an unfamiliar conspecific. The results showed that the aggressive behaviour was built up and broken down gradually depending on how long the two competitors had been together or apart. A decrease in aggressiveness was found after the sticklebacks had been together two weeks, with a further decrease after four weeks together. Conversely there was an increase in aggressiveness after the sticklebacks had been parted for two weeks or four weeks. The chance of food being equally distributed between the competing pairs increased with time spent together and decreased with time parted. The observed decrease or increase in the amount of aggression is discussed as a build-up or a breakdown of rank knowledge or of a co-operative partnership.     

Reactions of adult and immature squirrel monkeys to intergroup exposure

Initial encounters between unfamiliar animals raise the practical problem of controlling aggression and provide the opportunity to examine changes in social structure that may occur as groups merge. Social interactions and spatial grouping patterns were examined in newly formed squirrel monkey groups, in which a subgroup of familiar adults was introduced to a subgroup of familiar immature squirrel monkeys. Yearlings (10–11 months) and subadults (20–50 months) generally remained spatially distinct from adults, and intergroup interactions often consisted of adult-initiated antagonism. Adults exhibited sexual segregation in their spatial grouping patterns and interactions, whereas yearlings and subadults generally showed sexual integration. These data suggest that there is considerable adult resistance to integration of unfamiliar immatures into established adult social groups. Zoo Biol 17:519–524, 1998. © 1998 Wiley-Liss, Inc.     

The presence of the dam affects the efficiency of gentling and feeding on the early establishment of the stockperson-lamb relationship

This experiment investigates how the maternal presence influences the effect of additional human contact in early age on the reaction of lambs to their stockperson. Forty twin-born lambs were involved in this experiment during their first 4 days of life. Ten pairs of twins were reared artificially from 12h of age. One of each litter (AF, n=10) received 6.5+/-0.7 sessions of 30min of separation from the twin (with a wire fence) with 5min of gentling and feeding (suckling from a bottle and from a bucket fitted with a rubber teat). The other twin was not treated. Ten pairs of twins were reared with their dam and received 6.6+/-0.7 sessions of treatment. One twin (MAF, n=10) received the same treatment as AF. The other twin (M, n=10) was separated for 30min from the dam and had no human contact. From the age of 70+/-7h, lambs were tested in a social isolation test (alone for 1min, with the familiar stockman for 2min, alone again for 1min), in a Preference test (2min) between an unfamiliar maternal ewe and the familiar stockman, and, for the AF lambs only, in a Preference test (2min) between their familiar and an unfamiliar stockman. Eight AF lambs learned to suck on their own from the bucket of milk by the end of the experiment compared to only one MAF (P<0.001). AF lambs approached the human more (P<0.01), vocalised less (P<0.01) and walked less (P<0.01) during the social isolation test than animals reared with their mother (M and MAF). AF did not show any preference between the stockman and the unfamiliar maternal ewe while M and MAF lambs chose the ewe (P<0.05). AF lambs discriminated the familiar from an unfamiliar stockman only if they had learned to suck from the bucket during the treatment. Nevertheless MAF lambs vocalised less than M (P<0.05) in the presence of the stockman during the social isolation test, indicating a possible reduction of isolation distress. These results show that artificially reared lambs are preferentially motivated to interact with a familiar human after only a few days of contact. Moreover, they highlight the difficulty in using a feeding reward to improve the human-lamb relationship when lambs are reared permanently with their dams. However, the results suggest that early gentling improves the human-animal relationship whatever the maternal environment.     

Lactation and care for unrelated infants in forest-living ringtailed Lemurs

An adult female ringtailed lemur (Lemur catta) known not to have been pregnant showed spontaneous lactation in response to twin infants born to an unrelated female. The females had met only 7 months earlier, when they and two other unrelated adult females were released from separate locations in a forest enclosure to form a new social group. Three months after release, an adult male from an adjacent enclosure gained access to the new group for 1 day, the day of one female's estrus. No males had access to the females throughout the remainder of the breeding season. Within 2 weeks of the birth of the twins, one of the other adult females began carrying the infants frequently, typically one at a time. All three females were checked for lactation when the infants were two months old. Both their mother and the unrelated adult who had been carrying the infants were producing milk. The third adult female, who never carried either infant, had no milk. The third adult female, who never carried either infant, had no milk. This female, however, like the two maternal females, frequently attacked unfamiliar immigrating adult males when the males approached the infants. Potential implications of these observations concerning the social organization of ringtailed lemurs are discussed.     

The stimulatory effect of males on the initiation but not the maintenance of ovarian cycling in cotton-top tamarins (Saguinus oedipus)

Prior studies have shown that female cotton-top tamarins usually do not ovulate while living with natal groups, and most females do not ovulate until they are paired with an unfamiliar adult male. To examine the role of unfamiliar adult males on stimulating ovarian function, four cotton-top females were studied during three conditions: females living with their natal group for six weeks, living alone but exposed to a single unfamiliar adult male located 15 cm away from the female's cage for four weeks, and living with an unfamiliar adult male for six weeks. Behavior and urinary hormonal concentrations were measured during the three conditions. Exposure to the male consisted of visual, auditory, and airborne olfactory contact. First ovulation occurred during exposure to the unfamiliar male in three of the four females indicating that direct physical or sexual contact with the male is not required for onset of ovarian cycling. The fourth female did not ovulate even during six weeks of direct contact with the unfamiliar adult male. In addition, four parous females in either family groups (3) or singly caged (1) were examined for ovarian function 4–6 months after the death or removal of their mates. All femals continued to cycle in the absence of the male indicating that the male was not needed to continue ovarian cycling. In fact, two of the females were pregnant at the time their males died and both delivered normal infants and resumed cycling. The results of this study indicate that an unfamiliar adult male may facilitate the onset of ovarian cycling without being in direct contact with the female and visual, auditory, or airborne olfactory cues may be involved. Once repeated ovarian cycling occurs the male is not required to maintain ovarian function.     

Cortisol responses and social buffering: a study throughout the life span

The ability of specific adult females to moderate plasma cortisol responses throughout the life span was examined in male guinea pigs maintained in large mixed age/sex groups. At four critical life stages of social development (preweaning, periadolescent, sexually but not socially mature, and sexually and socially mature), the same male guinea pigs were exposed to the stressor of exposure to a novel environment for 4 h while either alone, with an unfamiliar adult female, or with a favored adult female, as based on objective criteria from behavioral observation at that life stage. In preweaning males (9-19 days of age), the favored female (biological mother), but not an unfamiliar female, reduced the cortisol response in the novel environment. In periadolescents (49-61 days), an unfamiliar female, but not the favored female, buffered the cortisol response. At the sexually but not socially mature stage (114-126 days), the cortisol response to novelty was depressed in all conditions, and not affected by either female. At the sexually and socially mature stage (270-330 days), the favored female, but not the unfamiliar female, moderated cortisol levels. These results corroborate previous findings in infants and full adults, demonstrate marked age-specific changes in the ability of females to buffer hypothalamic-pituitary-adrenal responses, and identify a heretofore undescribed period of cortisol response suppression in maturing male guinea pigs. The changing pattern of social buffering during the life span described here for the guinea pig might represent a more general pattern for males of other group-living mammals.     

Grooming,kinship, and co‐feeding in captive spider monkeys (Ateles geoffroyi)

Allo‐grooming is perhaps the most powerful affiliative behavior observed in non‐human primates. However, the functional significance of grooming in New World monkeys has not yet been fully understood, perhaps because grooming is less frequently observed in platyrrhines. To differentiate the potential role of affiliative investment and/or kinship on sharing access to food (co‐feeding) in spider monkeys, behavioral data on grooming, embracing, and feeding were collected from two different groups of captive study subjects: a familiar/kin group and a non‐familiar/non‐kin group. The results of this study suggest that family‐related spider monkeys that engage in grooming tend to share access to food resources more than unfamiliar conspecifics that do not groom. One explanation for this difference is that the unfamiliar study subjects had not yet invested in the affiliative social network, were not reciprocating their affiliative investments and hence, had a higher tendency toward single animal monopolizing resources. Degree of relatedness alone was not found to be a determinant for sharing the access to food, suggesting that familiarity in spider monkeys is based on the extent to which animals invest in affiliative relationships. In this study, only animals that had engaged in long‐term grooming and recognized each other as familiar shared the access to food. Therefore, it might be likely that in spider monkeys, long‐term grooming of high intensity has to be developed for co‐feeding to occur. Zoo Biol 20:293–303, 2001. © 2001 Wiley‐Liss, Inc.     

Familiarity with a partner facilitates the movement of drift foraging juvenile grayling (Thymallus thymallus) into a new habitat area

Preferring one social partner over another can enhance fitness. This paper reports that juvenile grayling were significantly more likely to enter and forage in new, upstream habitats when paired with familiar versus unfamiliar social partners. Fish paired with unfamiliar partners or when alone were more reluctant to enter the new area. The entry times for both fish in a familiar pair were significantly correlated, but uncorrelated for unfamiliar fish. These differences between familiars and unfamiliars were consistent over a 2-week period. Fish with familiar partners spent more time within three body lengths of each other than did those with unfamiliars. The results are discussed in relation to optimality models of drift foraging, which do not included sociality. It is suggested that the social dimension creates a more dynamic foraging response to variable environmental conditions and could have consequences for growth.     

Responses to a stranger mother-son pair in the wild chimpanzee: A case report

A stranger mother-son pair of the chimpanzee was observed twice interacting with conspecifics of a neighbouring unit-group: first, when the mother and son accidentally encountered them within the core area of the former; second, when the mother and son temporarily immigrated for about one week. On both occasions, the mother and son were severely attacked by adult males of the neighbouring unit-group, and would have been killed had it not been for human intervention. The main target of the aggression was not the infant, but the mother. Some adult males intervened and prevented other males and females from attacking the mother-son pair. Moreover, most adult males displayed an ambivalent attitude since they showed aggression towards them on one occasion, but groomed, reassured and played on another. The reasons for the variable responses of adult males to a stranger female are discussed in terms of possible differences in their mating strategies.     

Neural representations of personally familiar and unfamiliar faces in the anterior inferior temporal cortex of monkeys

To investigate the neural representations of faces in primates, particularly in relation to their personal familiarity or unfamiliarity, neuronal activities were chronically recorded from the ventral portion of the anterior inferior temporal cortex (AITv) of macaque monkeys during the performance of a facial identification task using either personally familiar or unfamiliar faces as stimuli. By calculating the correlation coefficients between neuronal responses to the faces for all possible pairs of faces given in the task and then using the coefficients as neuronal population-based similarity measures between the faces in pairs, we analyzed the similarity/dissimilarity relationship between the faces, which were potentially represented by the activities of a population of the face-responsive neurons recorded in the area AITv. The results showed that, for personally familiar faces, different identities were represented by different patterns of activities of the population of AITv neurons irrespective of the view (e.g., front, 90° left, etc.), while different views were not represented independently of their facial identities, which was consistent with our previous report. In the case of personally unfamiliar faces, the faces possessing different identities but presented in the same frontal view were represented as similar, which contrasts with the results for personally familiar faces. These results, taken together, outline the neuronal representations of personally familiar and unfamiliar faces in the AITv neuronal population.     

Within-group cannibalism by adult male chimpanzees

In the Mahale Mountains National Park, Tanzania, a young adult male chimpanzee was observed to feed on a 3-month-old male infant of the same unit-group. Four other adult males and an adult female shared the carcass. The mother of the victim had immigrated from a neighboring unit-group four years previously. Circumstantial evidence strongly suggests that the first-observed cannibal male also killed the infant. The adult male and the mother of the victim had been familiar socially and sexually with each other since the female immigrated. Since the mother of the victim had usually been ranging in the peripheral part of the unit-group's range, i.e., the overlapping area of the two unit-group's ranges during pregnancy and soon after birth, the infanticidal male might have had reason to suspect the paternity of her infant. Four such cases of within-group cannibalism by adult males suggest that the female range and association pattern before and after parturition are key factors allowing an infant to survive. The possibility of male-biased infanticide is also discussed.     

Nestling tree swallows (Tachycineta bicolor) alter begging behaviour in response to odour of familiar adults,but not their nests

Communication using chemical cues is important for many taxa, including birds, but the use of olfaction for intraspecific communication has been investigated only recently in passerines and is understudied in nestlings. To address this knowledge gap, we explored whether nestling tree swallows (Tachycineta bicolor) would recognize and respond to chemical cues of conspecifics, specifically testing begging responses to familiar and unfamiliar nest and adult odours. For the nest odour experiment, nests were treated with either orange essential oil or distilled water to create scented and unscented (control) odour environments, respectively. For the adult odour experiment, adults attending the nestlings were considered “familiar adults” and adults attending a different brood in the population were considered “unfamiliar adults.” We found that begging responses of nestlings did not differ in response to orange oil odour or water, but nestlings begged significantly longer and more intensely in response to odours of a familiar than an unfamiliar adult, regardless of adult sex. This provides evidence that tree swallows use chemical cues to alter their behaviour and opens up many exciting avenues of future research.     

Social and environmental factors affecting fecal glucocorticoids in wild, female white-faced capuchins (Cebus capucinus)

Assessing glucocorticoid levels in free-ranging nonhuman primates provides a means to determine the social and environmental stress load for individuals. We investigated the effect of four proximate variables--reproductive state, season, male rank stability, and dominance rank--on the level of fecal glucocorticoids (cortisol metabolites) in eight adult female white-faced capuchin monkeys in Costa Rica. Reproductive state, season, and male rank stability significantly affected fecal glucocorticoids while female dominance rank did not. Cortisol levels were significantly higher in pregnant females as compared with lactating or other reproductive states. Cortisol levels were higher among females during the dry season compared with the wet season, suggesting a metabolic adaptation to maintain homeostasis in drier, hotter conditions. Although unfamiliar males present a greater infanticidal threat than do familiar ones, we found that females experienced higher glucocorticoid levels during male rank instability events, regardless of whether the alpha male role was taken over by a familiar or an unfamiliar male. Our findings provide important benchmark and comparative data for future studies on the variables that affect glucocorticoid levels in this species and other mammals.     

Social enrichment of the environment with infants for singly caged adult rhesus monkeys

The practicability of social enrichment for singly caged adult rhesus monkeys was examined. Twenty-nine weaned rhesus monkey infants were removed from breeding troops to avoid overcrowding and were placed with unfamiliar singly caged adults. An adult-infant pair was considered compatible when (1) the two animals started huddling with each other within the first 5 days after pair formation and (2) the infant showed no signs of depression and took its share from a limited amount of favored food. Adult-infant pairs were compatible in 90% (26/29) of cases. Compatibility depended neither on the sex, age, and origin of the adult nor on the sex of the infant. There was no evidence that partners lost interest in each other during 7–11 months of follow-up observations. Three adults exhibiting stereotypical behavior abandoned their peculiar habits after they had lived with their young companions for 4 months. It was concluded that the often-heard notion that rhesus monkeys are highly aggressive should not prevent simple attempts to provide singly caged animals with a companion.     

Psychological well-being in paired adult female rhesus (Macaca mulatta)

We assessed the effects of social living (pairing) on improving the psychological well-being of adult female rhesus macaques (Mucuca mulutta) housed under laboratory conditions. We measured well-being in 12 pairs and 12 singly housed females through multiple indices of health (hematology, clinical morbidity, and body weight), stress (immune responses), behavior (preferences for social proximity, exhibition of species typical affliative behavior, and rates of abnormal behavior), and reproduction (frequency of ovulation, rates of conception, and infant survival). We selected adult females that had been living in single-unit cages and paired them in larger cages. Care was taken to allow females to become familiar with one another before pairing took place, and pairs that fought were separated before serious injuries occurred. Singly-housed control females were also paired for 1 week and then separated to balance the stressful effects expected to occur during the initial pairing and to assure that they were equivalent to the experimental animals in their ability to live socially. We concluded that pairing adult female rhesus monkeys was a positive experience for both the dominant and subordinate members of the pairs. They chose to spend the majority of their time involved in amicable social interactions, were more active, and they indulged in less nail biting than singly-housed controls. There were no differences in reproduction, rates of clinical morbidity, or immune stress responses among the groups. However, pairing alone may not be sufficient to assure the well-being of laboratory-housed rhesus macaques, because rates of abnormal behaviors such as stereotyped movements remained high. © 1994 Wiley-Liss, Inc.     

The Effect of Familiarity on Behavior of Kenneled Dogs During Interactions With Conspecifics

Kenneled environments often prevent direct physical contact between dogs, potentially causing stress, and so it has been recommended that such contact should be provided. This study examined the effect of familiarity on the behavior of dogs during off-lead interaction. Kenneled dogs (3 breeds) were given 15-min off-lead interactions with a familiar dog and an unfamiliar dog; the behavior of the focal dog and the distance between the dogs were recorded. More time in contact and interaction behaviors were recorded at 0 to 3 min with unfamiliar dogs than with familiar dogs. At 9 to 12 min, familiar pairs spent more time within 5 body lengths and more time being followed than unfamiliar pairs, who spent more time at more than 5 body lengths apart. This suggests that the initial interaction is more important when dogs are unfamiliar, but once this “greeting” has occurred, unfamiliar pairs are more likely to investigate their surroundings independently rather than together. Breed differences were observed only at 0 to 3 min. The study suggests that familiarity should be taken into account when assessing the effectiveness of conspecific contact as a potential enrichment for kennel-housed dogs.     

Social context and reaction to separation in peer-reared pigtail macaques: Some preliminary observations

The social environment affects both behavioral and physiological responses to separation from the mother. Less information is available on the impact of the social environment on the response to separation in peer-reared infant monkeys. This study reports the responses of peer-reared pigtail macaque infants to repeated separations, and the impact of social versus isolation housing during the separation. The responses of two pairs of monkeys were studied during four three-day separations. One of each pair was housed in isolation during the separation, and the other was with another pair of peers, with whom they had been living for one month prior to the separation. The isolation-housed peer responded to the separation with behavioral agitation, but no depression. The socially-housed peer's behavior did not differ from baseline during the separation. During successive reunions, all the separated monkeys, regardless of housing condition, exhibited declining levels of behaviors related to maintaining proximity to their attachment figure. Although the number of subjects is small, the results suggest that the presence of social support, in the form of a familiar peer, can ameliorate the response to separation, and that with repeated separations the responses of the monkeys changes significantly.