The study of things I have never seen.

Tinbergen defined structure as the momentary condition of an organism. Inference, interpretation, and theory were reserved for answering the "why" questions. Mason, however, observed that the study of behavior is incorrigibly mentalistic. Description seems barren compared to the richness supplied by creative intelligence. Exciting intervening variables such as learning, intention, and selective pressures can only be examined using inference, logic, and powerful deductive theories. For more than 100 years people have argued the two extremes: should science be restricted to the directly observable, or expanded to include what professional judgment could provide? I have devoted my life to the study of aggression and dominance, yet I have directly observed neither. I point to some behavior as an example of aggression, but I cannot provide an operational definition of what I mean. I will never know if another intends harm. I will never know if another is aware of the functions that behavior serves, and the outcomes that I confuse with past selective pressures and motivation. In a world where our subjects face extinction, perhaps it is wise to use computer simulations, to ask colleagues to rate their impressions, and to use logic to deduce behavior. The new "data" may be very useful. Still, I will miss actually watching what animals really do, even if I always describe it in terms of what I infer.

Counter aggression and reconciliation in Assamese macaques (Macaca assamensis).

Patterns of aggressive and affiliative behavior, such as counter aggression and reconciliation, are said to covary in the genus Macaca; this is referred to as the systematic variation hypothesis. These behavior patterns constitute a species dominance style. Van Schaik's [1989] socioecological model explains dominance style in macaques in terms of within- and between-group contest competition. Dominance style is also said to correlate with phylogeny in macaques. The present study was undertaken to examine phylogenetic and socioecological explanations of dominance style, as well as the systematic variation hypothesis. We collected data on counter aggression and reconciliation from a habituated group of Assamese macaques (Macaca assamensis) at the Tukeswari Temple in Assam, India. The proportion of agonistic episodes that involved counter aggression was relatively low. Counter aggression, however, occurred more often among males than among females, and it was most common when females initiated aggression against males. The conciliatory tendency for this group of Assamese macaques was 11.2%. The frequency of reconciliation was low for fights among males and for fights among females, but reconciliation was particularly rare for opposite-sexed opponents. Female social relationships were consistent with the systematic variation hypothesis, and suggest a despotic dominance style. A despotic dominance style in Assamese macaques weakens the correlation between dominance style and phylogeny in macaques, but it is not inconsistent with the socioecological model. Male-female relationships were not well explained by the despotic-egalitarian framework, and males may well have more tolerant social relationships than do females. Sex differences need to be considered when categorizing species according to dominance style.

Behavioral and cortisol responses to repeated capture and venipuncture in Cebus apella.

Eight capuchins were trained in a capture and venipuncture procedure. Samples taken immediately following capture indicated that subjects experienced rising cortisol levels over the first 5 weeks of training followed by a return to baseline (equivalent to day 1 levels) in the sixth and seventh weeks. After 7 weeks, samples taken 60 min after initial capture revealed that behaviorally habituated animals exhibited significantly lower cortisol levels in response to venipuncture as opposed to naive and experienced but nonbehaviorally habituated subjects. © 1996 Wiley-Liss, Inc.

Sex differences in adolescent rhesus monkey (Macaca mulatta) Behavior.

Sex differences in the behavior of 2.5- to 4.5-year-old rhesus monkeys, living in two social groups approximating natural compositions, were studied over a period of 3 years. Both sexes interacted significantly more often with members of their own sex in agonistic and affiliative interactions even when total rates and durations for male and female subjects did not differ. Strong sexual segregation was also seen in proximity, nonspecific contact, and huddling partners. Males were more involved in play and sex than were females and engaged in these activities primarily with other males. Females did more grooming than males, but groomed both male and female partners. Females also appeared to interact with a wider age range of partners than did males. Although total participation in aggressive interactions did not differ between the two sexes, females used more active forms of agonistic expression than did males. These differences in the behavior of adolescent rhesus are hypothesized to lead to social bonding among adolescent males, while females remain bonded to their matri-lines, including younger males and some fully adult males associated with matrilineal relatives. Adolescent males emigrate from their natal groups but retain sociality and bond to males and females in new groups as they become adult. © 1993 Wiley-Liss, Inc.

Kinship, association, and social relationships in rhesus monkeys (Macaca mulatta).

Data on social interactions with matrilineal kin were collected from two groups of rhesus monkeys for 6 years. All behavioral states, including time within one meter of another, involved kin more often than would be expected by chance. Significant associations were also found between kinship and the frequencies of various forms of agonistic as well as affiliative acts. Frequency of social interaction, however, was not a simple function of time in proximity. Although animals spent more time with kin than nonkin they had more aggressive interactions with kin. Moreover, aggression was biased toward the more serious forms of expression in interactions with kin. Time spent in association was neither predictive of the rate of aggressive interaction nor reduced by high rates of aggressive interaction. Rather than association time influencing rates of interaction, association time may be the consequence of a history of aggressive and affiliative exchanges. Preferential association and high rates of aggressive interaction with kin may be possible due to the existence of compensating social mechanisms nullifying the negative influence of specific aggressive encounters. © 1993 Wiley-Liss, Inc.

Testosterone changes during the period of adolescence in male rhesus monkeys (Macaca mulatta).

Testosterone levels of 59 male rhesus monkeys were monitored over a period of 5 years. Longitudinal comparisons revealed consistent rises in mid-morning levels of circulating hormone in successive years from age 2.5 to 6.5 years of age, whereas cross-sectional comparisons failed to detect significant differences among the older subjects. The first mid-morning hormonal elevation could be detected in some males as young as 2.5 years of age, whereas other males showed no detectable rises until age 5.5 years. Males showing first rises at later ages did not show hormonal levels consistently below age peers who had shown earlier rises. Extreme month-to-month variability and a failure to manifest the seasonal normal curve of fully adult males was characteristic of younger males, but some of these males, nonetheless, proved capable of fertilizing females. Although hormonal and agonistic dominance measures failed to show consistent correlations, the alpha male in an age cohort significantly more often had the highest testosterone levels. These data are used to argue that adolescence is a process that takes place over several years and that classification of adolescent animals as adults, based on a single criterion like fertility, has confounded many prior studies involving cross taxa comparisons as well as developmental variables.

Seasonal weight changes in male rhesus monkeys (Macaca mulatta).

Adult male rhesus monkeys lose weight during the breeding season and regain it during the nonbreeding season. The annual pattern of maximum weight gain just prior to the onset of breeding resembles the seasonal "fattening" seen in squirrel monkeys, but the period of weight gain is less discrete. The magnitude of weight change is less in younger males, in that sexually immature males gain weight in both seasons, but significantly less during the breeding season. Females do not lose weight during the breeding season. Post hoc analyses revealed no significant correlations between male testosterone levels, dominance ranks, weights, or weight changes. The heaviest animals as juveniles were predictably the heaviest as adolescents. The timing of seasonal changes in testosterone did not correlate with the timing of changes in weight; weight losses followed the rise in testosterone, and weight gains continued until early in the breeding season after testosterone levels had already begun to rise. It is suggested that seasonal hormonal changes may influence activities in individuals and that changes in the activities of particular group members may alter the activity patterns of other group members. This alteration of activity patterns due to group influences on individuals as well as individual influences on the group may explain why hormonal regulation of seasonal weight appears to be indirect and why individuals (juveniles) experiencing no seasonal hormonal changes nonetheless show differences in activity patterns and seasonal weight changes.

Wounding patterns in three species of captive macaques.

The incidence of wounding in captive groups of rhesus (Macaca mulatta), pigtail (M. nemestrina), and stumptail (M. arctoides) macaques was studied for 21 months. Groups were monitored daily for evidence of wounding. Wounded animals were captured, treated by veterinary staff, and returned following recovery. Records were kept on the age, sex, and species of the recipient, along with the type and location of wound. In each species of macaque, adult males incurred the highest frequency of wounds and multiple wounds of any age-sex class. This contrasted with previously reported behavioral data indicating low frequencies of aggression received by adult males, especially contact aggression and bites. These discrepancies indicate wounding frequencies do not necessarily correspond with behavioral measures of aggression. Inhibition of aggression directed toward infants and the selective avoidance of bites directed to vital body regions were presented as possible mechanisms that modify intragroup aggression. Increased wounding in the birth season under captive conditions suggests that the pattern of increased wounding reported during the breeding season under freeranging conditions may reflect xenophobic responses to immigrating males, rather than direct male-male competition for estrous females.

Patterns of affiliation among immature rhesus monkeys (Macaca mulatta).

The affiliative interaction patterns of the immature members of a group of rhesus monkeys at the Yerkes Regional Primate Research Center reflected a strong bias toward matrilineal kin, although this effect was modified by age and sex variables. Association with kin decreased with age, particularly for males. Juvenile males showed less of a kin bias in their behavior than did juvenile females, especially for grooming. Juvenile males also exhibited a preference for interaction with other males. The diminished association with kin and the same-sex bias may be reinforced in adolescence as adult males begin to aggressively target adolescent males involved in agonistic encounters with females or immatures. Adolescent males did not decrease their levels of social interaction relative to those of adolescent females; however, these males preferentially associated with other males (predominantly their own age-sex class) and specifically avoided females and younger animals, both kin and nonkin. Avoidance may diminish conflicts with females or immatures which could result from association, thereby decreasing the potential for selective aggressive interference by adult males. Juvenile and adolescent females maintained strong ties with their kin and preferentially associated with other females and immatures. The breadth of interaction of females with other females may facilitate the establishment of dominance relationships as females mature. Familiarity and predictability may also decrease the necessity of more severe agonistic interaction.

Modification of aggression through socialization and the special case of adult and adolescent male rhesus monkeys (Macaca mulatta).

Significant differences exist in the frequencies with which age-sex classes of rhesus macaques engage in agonistic interactions with other age-sex classes. In the study reported here, individuals engaged in significantly more agonistic interactions within their own age-sex classes, but, adult females also showed significantly more aggression toward infants and young females whereas adult males directed significantly more aggression toward adolescent males. Infants directed aggression toward infants of both sexes, but adults showed significantly less aggression toward adults of the opposite sex. These findings are hypothesized to reflect (1) competitive conflict among those individuals in the group most similar to each other (members of the same age-sex class); (2) the protection and socialization of offspring by adult females; and (3) the modification of adolescent male aggressive expression by the selective interference of adult males. As a consequence of adult response to the agonistic behavior of adolescent males, maturing males (1) selectively target other older males, avoid aggression against females and immatures; (2) form alliances with other males; and (3) become progressively isolated from their matrilines.

Agonistic aiding: Kinship, rank, age, and sex influences.

An analysis of 3,774 episodes of agonistic aiding collected during a two-year study of a rhesus monkey group (Macaca, mulatta) indicated the differential influence of kinship and rank relationships on the participation of different age-sex classes in both aid to victims and aid to aggressors. Most aiding favored victims rather than aggressors and was much more likely to occur when matrilineal kin were involved. Females were more likely to aid than were males, and the frequency of their participation increased with age. Females were much more influenced by kinship than were males and defended or aggressively supported kin against any third party regardless of dominance relationships. Adult males seldom aided against animals that were dominant to themselves; the rare exceptions occurred when adult males defended kin. Aiding was far more likely to occur if the victim was squealing, and noisy agonistic episodes often involved multiple aiders on both sides. Aiding patterns had some potential to insure dominance rank inheritance within families, in accordance with the Kawamura hypothesis. In aiding animals outside of their own matrilines, however, group members aided randomly with respect to this model. There was little evidence that aiding functioned to support individuals when they targeted animals to which they should be dominant as adults based on matrilineal dominance relationships. Most defensive aiding seemed to function primarily to defend victims (primarily kin) of aggression. Aggressive support of the attacker, on the other hand, seemed to function primarily to reinforce coalitions with the attacker. The identity of the victim was unimportant as long as it was neither kin to nor dominant to the aider. Aggressive support of attackers did not overturn existing dominance relationships.