Social interactions among captive brushtail possums (Trichosurus vulpecula)

A biological control strategy relying on a self-disseminating agent may provide the only affordable long-term technique for reducing brushtail possum (Trichosurus vulpecula) numbers throughout New Zealand. The objective of this study was to determine the frequency and patterns of social interactions in single and mixed-sex groups of possums, in order to identify interactions that may assist in the dissemination of biocontrol agents. Thirty-two sexually mature wild-caught possums (16 female, 16 male) were housed in captive groups (of four) in enclosures during the breeding and non-breeding seasons. Groups consisted of either all females, females and males or all males. Four types of social interactions were defined: threats, fights, affiliative and sexual interactions. Interactions only occurred between two animals at one time and were most frequent in the non-breeding season. Within all female groups, possums readily engaged in interactions that had either an agonistic or affiliative nature. Mixed-sex groups interacted less frequently than females, but also engaged in both agonistic and affiliative interactions. In contrast, possums in all male groups rarely interacted, with only a few fights and no affiliative interactions observed. Some mixed-sex dyads appeared to 'associate' during the breeding period. Young were produced by three females that regularly associated with a male and one female that showed little associative behaviour. Given the different interaction patterns observed in each group type, biological control agents that rely on specific interaction patterns for dissemination, are likely to spread at different rates among different possum groups and in different seasons.     

Social cues and hormone levels in male Octodon degus (Rodentia): a field test of the Challenge Hypothesis

Social interactions are important factors determining and regulating individual behaviors. Testosterone has been related to agonistic interactions, while glucocorticoids have been related to social stress, especially during interactions of dominance. We compared testosterone and cortisol concentrations in male degus (Octodon degus, Rodentia) under laboratory conditions without male social interactions, with data from wild males in nature. Under natural conditions, males should present higher levels of testosterone during the breeding season due to social interactions (Challenge Hypothesis). Alternatively, intense social instability could act as a stressing environment, raising glucocorticoids, which inhibit testosterone concentrations. Our results show a significant increase in agonistic interactions between males during the breeding season, and disappearance of non-agonistic male interactions during this period. Hormone levels in breeding season show nonsignificant differences between laboratory groups, but testosterone concentrations in field males were significantly higher than in laboratory males. Testosterone levels were similar among pre-breeding and breeding periods, but in field animals the concentration was approximately 30% higher than in laboratory degus. In field animals, we found two different mating strategies: resident males, with territorial behavior, and transient males, displayed an opportunistic approach to females. Finally, cortisol presents a similar pattern in both laboratory and field animals; pre-breeding values of cortisol are higher than during the breeding season. This suggests that social interactions in O. degus activate a rise in testosterone, supporting the Challenge Hypothesis, and could be considered as partial support of the Social Stress Hypothesis.     

Social boundaries in a Malagasy Prosimian,the Sifaka (Propithecus verreauxi)

Using focal animal samples, the social organization of sifakas was studied in two forests for 2500 hr spread over 18 months. Data were also obtained on the size and composition of groups at two other sites. The size and adult sex ratio of groups varied widely within populations, although population-wide sex ratios approached unity. During the brief annual mating season, some males mated with females belonging to other groups. The response of both male and female group members to the approach of a nongroup male appeared to depend on his identity. It is argued that while group size may be constrained by the availability of resources, group composition reflects the effects of small-sample demographic variations rather than the outcome of reproductive competition among or between males and females. Spatial boundaries of groups do not coincide with social or reproductive boundaries even within a single breeding season; further study is needed of the processes whereby relationships are established and maintained between individuals from different groups.     

Agonistic and grooming behavior of captive crowned lemurs (Lemur coronatus) during the breeding season

Captive breeding of rare and endangered prosimians may be enhanced by an increased understanding of all aspects of their seasonal mating behavior. In this study, the agonistic and grooming behaior of captiveL. coronatus were studied during their annual breeding season. Between October and March, selected aspects of agonistic and grooming behavior of four male-female groups were recorded. Males initiated significantly more allogrooming than females. The frequency of this behavior pattern increased significantly in the weeks of estrus. Females performed significantly more agonistic behavior patterns than males. The mean frequency of agonistic interactions decreased significantly during the breeding season. In successfully reproducing groups males showed much less agonism towards females, than they did in unsuccessful groups. Inter-specific comparisons demonstrated that the patterns of agonistic interactions during the breeding season are very different among closely related species of lemurids. The conclusions drawn from this study are that captive breeding of crowned lemurs may be enhanced by keeping permanent multi-male, multi-female groups.     

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.     

Within-group social relationships among females and adult males in wild western lowland gorillas (Gorilla gorilla gorilla)

Within-group female relationships, and relationships between females and adult males have not been described for wild western lowland gorillas. New data are presented here from Mbeli Bai in the Nouabale-Ndoki National Park, Republic of Congo. Nine groups were observed over a continuous 2-year period, and affiliative and agonistic interactions, as well as time spent by females and adult males in proximity to each other were recorded. Affiliative behavior was extremely rare in the bai, and measures of proximity between individuals were inconclusive because of the small sample sizes. Rates of agonistic interaction among females were highly variable between groups. The majority of agonistic interactions were undecided, and the supplant rate was low. Evidence for an agonistic dominance hierarchy is weak. The data do not support hypotheses that increased frugivory in western lowland gorillas raises levels of within-group contest competition; however, the need for intersite comparisons is stressed. In contrast, rates of agonistic behavior between females and silverback males were higher and more consistent between groups. Agonistic relationships between males and females conformed with patterns seen in mountain gorillas, where male protection from intraspecific aggression is important. The benefit females gain by forming long-term cooperative alliances appears to be small, and is likely outweighed by reproductive advantages associated with male protection.     

Gender effects on aggression, dominance rank, and affiliative behaviors in a flock of captive adult cockatiels (Nymphicus hollandicus)

Agonistic and affiliative behaviors and spatial positioning were studied in a small psittacine species, Nymphicus hollandicus. Subjects studied were flock-housed breeders including five hens and seven cocks. Fifteen-minute focal animal samples were collected for the entire flock in a randomly distributed order during mate selection and the onset of the breeding season. All agonistic behaviors were recorded, including the winner and loser of each interaction, along with allopreening and copulation behavior. Point samples were recorded every 60s to determine social spacing. Rates of aggression were significantly higher for male cockatiels than female cockatiels. Results based on dyadic agonistic interactions showed males to rank significantly higher in the social hierarchy than females. Associations within the flock were not random. Individual birds associated more with specific birds than would be predicted by chance. Analysis of spatial data revealed that there were both same-sex and opposite-sex preferred associations within the flock. Male cockatiels engaged in allopreening behavior with females significantly more than with other males. Observations of breeding and nesting behaviors revealed pairs, a triad, and extra-pair mating.     

Social interactions and aggression among male Madagascar hissing cockroaches (Gromphadorhina portentosa) in groups (Dictyoptera: Blaberidae)

We studied agonistic interactions among male Madagascar hissing cockroaches,Gromphadorhina portentosa, in groups of five (low-density) or 10 (high-density) males. Consistent with previous studies of male pairs, we observed aggression (Abdomen Flick, Abdomen Push, Butt, Lunge), submission (Crouch, Retreat), and noncontact behavior (Abdominal Extension, Abdomen Thrash, Agonistic Hiss, Stilt). Males at both densities performed all acts. However, males in the high-density group performed Abdomen Push significantly more often than males at a low density. The rate of each remaining act was unaffected by density. Regardless of density, males within social groups varied in aggression. More aggressive males utilized frontal assaults (Butt and Lunge) during interactions, while males displaying lower levels of aggression preferentially used the abdomen during interactions. More aggressive males performed Abdomen Flick more frequently, while males displaying lower levels of aggression performed Abdomen Push. We also investigated the relationship between male aggression and the four noncontact behaviors. We found that Abdominal Extension, Abdomen Thrash, and Agonistic Hiss were positively correlated with our aggregate measure of male aggression suggesting these are aggressive displays. Stilt was positively correlated with measures of both aggression and submission, leaving its function unclear. None of the behavioral acts examined in this study were highly correlated with male weight. Our results are discussed in light of possible hypotheses addressing the function of specific behavior during male-male competition.     

Social organization of free-ranging ruffed lemurs,Varecia variegata variegata: mother-adult daughter relationship

The relationship between a mother and an adult daughter is examined in a group of free-ranging ruffed lemurs (Varecia variegata) at the Duke University Primate Center (DUPC). Although the two females were affiliative during the birth season, interactions during the mating season were predominantly agonistic. The maturing daughter was dominant to the mother, as has been observed in many caged social groups at the DUPC. Although both mother and daughter produced offspring in the same group, the daughter subsequently aggressively evicted the mother from the enclosure. It was not possible to maintain more than one long-term resident breeding female in the same social group. This pattern contrasts with observations of affiliation among breeding females in the wild. © 1992 Wiley-Liss, Inc.     

Demography, range use, and behavior in black lemurs (Eulemur macaco macaco) at Ampasikely, northwest Madagascar

We studied a black lemur population over a 2-year period (1992-1993) and 8 years later (2000) in a 50-ha secondary forest in northwest Madagascar. All of the animals were marked to investigate population dynamics and seasonal variation in ranging and behavior, and new data on black lemurs were obtained. Our data on demographic characteristics were expanded to include other forest sites and contrasted with those collected in other Eulemur macaco macaco field studies, in relation to human activity and the presence of introduced and cultivated plant species. Density is affected by deforestation and hunting. Group size and home range depend on the composition of the forest and probably food patches. Sex ratio at birth varies according to the number of females per group, a result that fits the local resource competition model. Groups are multimale-multifemale, and adult females form the core of the groups. Reproductive parameters indicate sharply defined seasonal breeding, a high female reproductive rate, and birth synchrony. Changes in group composition reveal male and female juvenile dispersal, male transfer between groups at the time of mating, and adult female transfer and group fission when groups exceed a critical size. At mating and birth, intergroup agonistic encounters occurred at home-range boundaries, and larger groups were dominant over smaller groups. Patterns of intragroup interactions suggest that males compete for access to groups of females during the mating season, and that females may compete for food resources during the birth season. Our study also reports female social dominance and lack of sexual weight dimorphism in this species.     

Seasonal Differences in Social Behavior among Adult and Juvenile Meadow Voles,Microtus pennsylvanicus

Seasonal differences in behavioral interactions between wild-caught adult and juvenile meadow voles, Microtus pennsylvanicus, were measured in paired encounters in a neutral arena. Seasonal differences existed in the adult-juvenile paired encounters. Early in the breeding season (May—Aug.) paired encounters between adult males and juvenile males were more agonistic than other adultjuvenile pairings. Late in the breeding season (Sep.—Dec.) adult female-juvenile male encounters were more agonistic than other adult-juvenile pairings. Odor preferences of juveniles were determined in a Y-maze olfactometer. Juveniles did not demonstrate seasonal differences in odor preference. Males preferred the odor of adult females to the odor of adult males or their own odor. Females preferred the scent of an adult male to the odor of an adult female, but did not show a preference between their own odor and the odor of an adult male or an adult female. The results are consistent with hypotheses that state in a promiscuous species, females should be philopatric, and males should disperse as a consequence of adult competition. The data suggest that agonistic behavior by adults may regulate juvenile dispersal and recruitment, and define the composition of overwintering groups.     

Social Interactions of Yearling Male Fallow Deer during Rut

Despite a low probability of achieving copulations, yearling male (1.5-year-old) fallow deer Dama dama display behavioural changes during rut, interacting with both females and older males. Juvenile interactions in polygynous ungulates may affect further reproductive success through both motor training for future interactions and/or competition for current resources that affect growth. To test this hypothesis, we intensively studied the behaviour of 12 yearling males in two captive populations during a rutting season. Interactions with females were interpreted as motor training aimed at learning to recognize oestrous females, because yearling males rarely interacted with their mother and because interactions essentially consisted of olfactory investigations focused on oestrous females. Because agonistic interactions with older males never involved physical contact and were mainly initiated by the most dominant buck in each population, we concluded that these interactions resulted from the presence of the yearlings close to oestrous females defended by rutting males. Heavier yearlings tended to be dominant over lighter ones and tended to interact more frequently with other animals, suggesting that early growth may influence the ontogeny of social behaviours.     

Social interactions among female rhesus macaques (Macaca mulatta) during the nonbreeding season: Responses to the introduction of males

When rhesus monkeys are observed in social groups during the breeding season, increases in interfemale aggression coincide with midcycle increases in sexual activity between males and females. However, some investigators have suggested that both aggressive and affiliative interactions between females are influenced by the presence or absence of males, irrespective of menstrual cycle stage. In the present study, social interactions among members of a captive group of rhesus females were measured during the non-breeding season in response to the introduction of rhesus males. Ovariectomized rhesus females (estrogen-treated or untreated) served as stimulus controls. Tests with males were characterized by significantly decreased interfemale proximity and grooming and significantly increased aggression from that seen in tests with stimulus females or in the absence of stimulus animals. Only interfemale proximity declined significantly during stimulus female tests, but results suggest that this may merely reflect a decline in this behavior that occurs across the course of the day. Estrogen treatment did not alter either the aggressive or affiliative behavior of stimulus females or group female response to stimulus females. The possibility is discussed that changes in interfemale interactions during tests with males reflect female interest in interacting with the male, particularly under social conditions that may limit such interactions.     

Social relationships of immigrant and resident female mountain gorillas. I. Male-female relationships

Adult males are important social partners for all females in mountain gorilla social groups, but male-female relationships can vary in association with variation in female residence status, male age and mating status, and relatedness. Such variation occurred in a large group observed over a 3-year period. All females associated and interacted affiliatively relatively often with a young silverback with whom all mated. Long-term resident females also did so with an old, non-breeding male to whom most were related, but recent immigrants spent little time near him and had few non-aggressive interactions with him. The old male made agonistic interventions to support relatives; interventions in female conflicts by the younger male tended to ameliorate competitive differentials that immigrants faced and may have helped him to retain them as mates. Males aggression toward females was common, most probably served as a mating tactic, and did not involve resource competition. Extensive grooming by an adolescent male suggests that males may also use affiliative behavior to develop mating relationships. Females may have competed for proximity with and social access to the younger silverback; competitive success could influence how well females and their offspring are protected by silver-backs, but the extent of such competition was not clear. Large group size may have heightened differentiation of male-female relationships and competition among females, but comparative data from smaller groups generally corroborate the findings from the large group. © 1992 Wiley-Liss, Inc.     

Factors affecting aggression among females in captive groups of rhesus macaques (Macaca mulatta)

Captive groups of primates often exhibit higher rates of aggression than wild, free-ranging groups. It is important to determine which factors influence aggression in captivity because aggression, particularly intense aggression, can be harmful to animal health and well-being. In this study, we investigated the effect of ground substrate as well as season, rank, age, and group size on rates of agonistic interactions per female in seven captive groups of rhesus macaques (n = 70 females, 1,723 focal samples) at the California National Primate Research Center. Agonistic interactions were divided into three categories: displacements, mild aggression, and intense aggression. Females living in enclosures with gravel substrate were 1.7 times more likely to be involved in intense aggression (e.g. chases and physical contact) than females living in enclosures with grass (Poisson regression model: P < 0.001). High-ranking females were at least 1.3 times more likely to be involved in mild (e.g. threats and lunges) aggression than lower-ranking females (low rank: P = 0.03; mid rank: P = 0.001). Females of all ranks were 1.5-1.9 times more likely to be involved in both intense and mild aggression during the breeding season than other seasons. Age and group size did not affect rates of mild or intense aggression. These findings indicate that although some aggression appears to be natural and unavoidable, i.e. aggression during the breeding season, the well-being of captive macaques can be improved by developing grass substrate in outdoor enclosures.     

Sex, Rank and Age Differences in the Japanese Macaque (Macaca fuscata yakui) Participation in Inter-Group Encounters

In many species interactions among group are often characterized by agonistic behaviour. Although animals may participate in inter‐group encounters in different ways, depending on their energetic requirements, reproductive tactics, and/or developmental stage, the proximate causes affecting an animal's participation in inter‐group encounters are still poorly understood. Indeed, many studies have analysed the behaviour of males and females during inter‐group encounters without considering the importance of additional factors (e.g. rank). This study focuses on wild non‐provisioned Japanese macaques (Macaca fuscata yakui) living on Yakushima Island, Japan. It aims to determine how monkeys of different sex, age, and rank behave during inter‐group encounters and it discusses the implications and consequences of their behaviour on group composition and male dispersal. Males participated significantly more than females in inter‐group encounters, by displaying more aggressive or affiliative behaviour. High‐ranking and/or adult males were more aggressive than low‐ranking and/or subadult males during encounters occurring in the mating season and they also showed more herding behaviour. This trend was not found in inter‐group encounters occurring during the non‐mating season. Finally, males which then emigrated to new groups were low‐ranking and/or subadult individuals. Those males displayed more affiliative behaviour towards foreign males than males which did emigrate. These data indicate that in non‐territorial species with male dominance over female and high competition for mating partners males play an active, and often aggressive, role during inter‐group encounter while female participation is scarce. Factors such as age, rank and period of the year (in seasonally breeding species) have to be taken into considerations when analysing interactions between groups and their effects on group composition and social behaviour.     

Social dominance does not increase oxidative stress in a female dominance hierarchy of an African cichlid fish

In many group living animal species, individuals use aggression to gain and maintain social dominance to secure access to ecological resources and potential mates. While social dominance has many fitness benefits, there are also potential costs associated with frequent agonistic interactions and status display. One potential cost of social dominance is oxidative stress, the imbalance of reactive oxygen species and antioxidant capacity. In the cichlid species Astatotilapia burtoni, dominant males are aggressive, hold a breeding territory, and have an activated reproductive system resulting in larger gonads. Subordinate males are submissive, school with females, and are nonreproductive. Females are submissive under natural conditions, but in a female-only group, a dominance hierarchy will form with dominant females taking on male-typical behaviours including aggression, territory defence, and increased androgen levels. However, in contrast to males, social dominance is not linked to increased activation of the reproductive system in females, allowing us to test whether social dominance alone exposes individuals to increased oxidative stress. We compared dominant and subordinate females in female-only groups in five markers of oxidative stress. Dominant females did not have higher levels of oxidative damage compared to same-sex subordinates. This result contrasted to the trend in males in which dominant males had higher oxidative damage than their subordinate counterparts. Our findings suggest that the oxidative cost of social dominance is limited and support the notion that previously reported associations between high rank and increased oxidative stress is most likely driven by increased investment in reproduction.     

Sociality in Callithrix penicillata: II. Individual Strategies During Intergroup Encounters

In social animals, intergroup interactions, whether through agonistic and competitive behaviors or affiliative ones, can influence important parameters such as home range, territory sizes, and access to resources, which may directly affect both female and male fitness. We studied the intergroup interaction patterns of a wild group of black-tufted-ear marmosets (Callithrix penicillata) in central Brazil. Agonistic interactions occurred at low frequencies during intergroup encounters. The marmosets directed agonistic interactions without physical aggression primarily against same-sex individuals, suggesting that male and female aggression patterns are shaped by their sexual interests. However, females of the focal group also directed agonistic behavior toward extragroup males that attempted copulation. The marmosets appeared to use intergroup encounters to gather information about possible partners and extragroup reproductive opportunities. Intergroup sexual interactions occurred mainly in the form of copulations or attempted copulations by all adults, with the exception of the dominant female. Our results suggest that a possible reproductive strategy used by males is to attempt fertilization of extragroup females. Adult males copulated with the same extragroup female during several opportunities, which suggests sperm competition or the establishment of social bonds with neighboring females.     

Number of males in primate groups: Comparative tests of competing hypotheses

Primate social groups frequently contain multiple males. Male group size has been hypothesized to result from male mating competition, but the selective factors responsible for the evolution of multimale groups are unclear. Short breeding seasons create situations that are not conducive for single males to monopolize mating access to females, and may therefore favor the formation of large male groups. Alternatively, since the costs of mate defense increase with the spatial clumping of females, female group size may be a primary determinant of the number of males in a primate group. We used comparative methods designed to control for the potentially confounding effects of hidden third variables associated with phylogeny to test the breeding season and female group size hypotheses for the evolution of multimale groups. Our results revealed no association between breeding season duration and the number of males in groups. In contrast, we provide support for the female group size hypothesis by demonstrating a strong pattern of correlated evolution between female and male group size. © 1996 Wiley-Liss, Inc.     

Relations between group size and composition and feeding competition in mountain gorilla groups

The intensity and patterning of interference competition for food within mountain gorilla (Pan gorilla beringei) social groups is influenced in several ways by group size and composition and varies within and across age/sex classes. Data on 251 spatial displacemtnts associated with feeding, collected during a 17-month study of mountain gorilla feeding ecology, show that overall displacement rates and displacement rates for individuals were positively correlated with social group size. Silverback males were responsible for a disproportionately high number of displacements. Adult females also were involved in competitive interactions over food more often than expected from their representation in groups, and had feeding bouts interrupted disproportionately often, principally by other females and by silverbacks. Competitive relationships between females varied in association with female dominance rank and age, but were not clearly associated with relatedness between females. The results support the argument that social foraging entails a cost which is proportional to group size and which falls particularly on adult females. The comparatively low rates of competitive interactions, however, suggest that this cost is relatively low, and that female mountain gorillas sacrifice little in terms of feeding efficiency by living in social groups.