This phenomenon is well illustrated by examples of intertroop encounters. When two troops meet or share the same resources, their behavior is based on dominance (Minnesota Zoo 2003). Thus, there is potential for aggressive behavior. Two troops, the Shiga C and Shiga B troops, have been observed to share portions of their home ranges during the autumn and spring. Because food is most plentiful and of highest quality during these seasons, the two troops can easily share the same resources without significant conflict. In contrast, increased levels of intertroop agonistic behavior have been observed between troops sharing resources during times of food scarcity (Wada 1980).
Similarly, captive troops of macaques sometimes have increased levels
of aggression because of their confinement to spaces that are smaller
than their natural range. For example, the Oregon troop is kept in a
.8 ha space (Alexander & Bowers 1968, as cited in Clark 1978). This
close confinement keeps the alpha male from engaging in many characteristic
actions, such as directing movement of the troop, protecting members
from predators, and leading encounters with neighboring troops. As a
result, troop members did not cluster around the alpha male as much as
they do in the wild, and instead formed small groups based on play, feeding,
and grooming (Alexander and Bowers 1968, as cited in Clark 1978). Because
of this adapted social organization, troop members were very aggressive
and not well controlled by the alpha male (Clark 1978). Conversely, if
a captive troop is not closely confined, it may experience a decrease
in intratroop conflict because of the ample supply of food and protection
from predators that the captive environment affords. As a result, the
alpha male may give up the role of controlling troop conflict.(Wantanabe
1979).
Mating season is another time of peak aggression in Japanese macaque troops. The author suggests that increased levels of testosterone in males during the mating season correlates with the high aggressive activity (Nigi 1980 as cited in Enomoto 1981). Chasing, hitting, and kicking, and biting are examples of agonistic behavior that can occur between individuals of a mating pair (Enomoto 1981). One study has shown that during the mating season, frequencies of copulation, male chasing of females, and vocalizations associated with tree-shaking (a male competitive behavior) increased. During the non-mating season, dominant males chased females most frequently. However, the link between dominance rank and chasing behavior is not strong during the mating season, reflecting the increased aggression (Enomoto 1981). The daily frequencies of male chasing had a positive correlation with the number of females in estrus that day. Estrus females were chased more frequently than those not in estrus. Males usually chased females who were alone, though they occasionally chased females who were sitting with another male. Male chasing and attacks toward females sometimes caused injury to the females, and injuries in males during the mating season were usually the result of inter-male agonistic encounters (Enomoto 1981).
An observational study conducted with the Arashiyama
West troop indicates that changes in a troop’s dominance hierarchy
are also frequently accompanied by aggression. In this instance, a
mid-ranking female began
attacking the alpha female after the alpha displayed stiffness in her
limbs that impaired her daily activities. At first, the alpha male defended
her against the subordinate female, but mid-way through the process he
abandoned his old alliance and began helping the new alpha female instead.
Once the rank change was underway, the kin of these two females also
began engaging in agonistic encounters to facilitate their own rank changes.
In addition, the original alpha female sometimes redirected her aggression
by attacking an uninvolved low-ranking female after being attacked by
the new alpha female. By the time the rank changes were complete, the
kin of the new alpha female were dominant over the kin of the old alpha
female. Rank changes were believed to be complete when grooming was observed
between the old and new alpha females, indicating that stability had
returned to their relationships (Gouzoules 1980).
Agonistic behavior includes both
aggressive and submissive behaviors. In a study on the Arashiyama West
troop (a captive troop), several forms of agonistic behavior were observed.
Forms of attack listed include threat, chase, punishment, and assault.
Threat is defined as pursuit longer than 5 meters, or any aggressive action
toward another individual (screaming, pursed lips, woofing, ear-flipping,
gaping) paired with a lunge that induces the individual to move away. Chase
is recognized as directed pursuit and aggressive behavior toward an individual.
Punishment consists of physical contact that does not result in injury,
such as slapping, hair pulling, quick biting. Finally, assault is defined
as physical contact that does cause injury, such as biting, shaking, gnawing.
Forms of submission were also identified. Form A is indicated by lack of any sort of reaction by the attacked individual. Form B consists of the aggressee running away from the aggressive individual for more than one meter. Form B is also defined as a fear grimace, a cringe, or short vocalizations. Form C consists of prolonged screaming, and D is expressed by the attacked individual retreating to a corner with its head toward a wall. It was observed that the more aggressive the encounter, the more serious the act of submission. Defense behavior by one macaque on behalf of another was also observed (Clark 1978).
In the same study, specific types of agonistic interactions were also
noted. Mobbing, or Troop Attacks, occurred more frequently in this
transplanted troop than it does in free-living Japanese macaques,
probably due to the inability of the peripheral males to distance themselves
from the core of the troop during its initial period of confinement.
Many mobbing encounters were initiated by a juvenile toward a peripheral
male, after which several dozen macaques joined in and continued
the
encounter for up to 20 minutes. Some of these troop attacks ended
when individuals began grooming the victim of the attack (Clark 1978).
Thus,
one of the functions of grooming is to bring reconciliation after
an aggressive encounter (Minnesota Zoo 2003).
93% of all agonistic encounters observed were initiated by adult
females or juveniles. Juveniles, followed by adult females, were
also the recipients of the highest percentage of agonistic encounters.
However, immediately after the confined troop was released into
a larger enclosure, all forms of severe agonistic behavior stopped,
and the troop re-formed the characteristic central-peripheral social
organization (Clark 1978).
In addition, aggression sometimes occurs between parents and offspring. For example, orphaned mothers (primiparous and multiparous) showed frequent aggressive behaviors toward their infants. However, orphaned mothers' aggressive behavior often decreases as they have raise more offspring and gain maternal experience. Mothers also exhibit aggressive behavior toward allomothers when their infants are too young to be handled by younger females. In addition, when an infant approaches an adult male, he usually runs away or pushes the infant away (Hiraiwa 1981).
When individuals in a troop engage in agonistic encounters, for whatever reason, a third macaque will often form a temporary "alliance" with one of the members of the conflict. An actor alliance is formed when the third individual sides with the original aggressor, while a reactor alliance occurs when the third individual sides with the aggressee (Wantanabe 1979).
In a study observing a free-ranging troop of Japanese macaques in Japan, 698 out of 6,794 observed agonistic encounters involved third individuals who formed an alliance with one party. Most troop members (except for infants) were involved in an alliance at some point. The dominant male formed alliances somewhat equally with members of nearly all matrilineal groups. However, the most dominant females did not ally often with the dominant male, probably because their rank protected them from being frequently attacked and needing such an alliance. (Wantanabe 1979).
Individual alliances formed alliance networks within the troop. The alpha male was the focus of the networks, and each matrilineal group formed a cluster around him. The alpha male most often engaged in reactor alliances, which the author postulates may have contributed to reducing intratroop conflict by punishing aggressors and aiding lower ranking animals. Thus, the presence of alliance networks sometimes prevents high ranking animals from attacking those of lower rank because of the support the lower ranking animals may receive from other individuals. In the same way, alliances allow lower ranking animals to attack higher-ranking individuals (Wantanabe 1979).
Reactor alliances often formed between individuals of the same age. Older animals initiated alliances more frequently than younger animals did. Adult peripheral males usually participated in actor alliances, especially if the agonistic encounters involved immature macaques (Wantanabe 1979). Most macaques (except the alpha male) allied with the higher-ranking member of an encounter and attacked the lower-ranking member. However, if an infant was attacked, troop members often allied with it and were very protective of it (Wantanabe 1979).
A large portion of adult female alliances
were reactor alliances, occurring most frequently when the participants
in the agonistic
encounter
were their own offspring. Of all troop members, mothers intervened
most often in encounters between immature individuals, always allying
with their offspring. They were even aggressive toward dominant animals
if they were intervening on behalf of their offspring. In such cases,
the dominant animal often redirected its aggression onto the mother.
When a mother intervened in encounters between two of her own offspring,
she always sided with the younger one. In a similar fashion, if encounters
occurred between members of different matrilines, the intervening animal
would always ally with the member of its own matriline. Thus, members
of the same matrilineal group can inherit their mother’s rank
through the protection they receive from other members of their matriline
(Wantanabe 1979).