Social interactions among adult male langurs (Presbytis entellus) at Rajaji Wildlife Sanctuary

A population of langurs (Presbytis entellus)at the Rajaji Wildlife Sanctuary in northern India was investigated for 1820 hr throughout a 10-month period in 1978. Data were collected from four bisexual troops and the adult males that ranged outside of bisexual troops. Most (60%) of the observation hours occurred with a main study troop from which social and ecological data were collected. The langur population at Rajaji shows pronounced birth and mating seasons. The population density is high (ca. 80/km ²), with about 75% of the adult males living outside of bisexual troops, which typically are large and multimale. Males outside of bisexual troops occur in small all-male bands or as isolates. Relations between bisexual troops and all-male bands are characterized by relatively low levels of aggression, and members of all-male bands are able to associate with bisexual troops for prolonged periods during the mating season. As a result of these associations, nontroop males are about as successful as troop males in achieving reproductive access to troop females. These associations between bisexual troops and all-male bands occurred with a minimal amount of agonistic behavior and without mortality or injury to troop females or immatures.     

Reactions to fear as a proximate factor in the sociospatial organization of baboon progressions

The objective of this study was to test the hypothesis that fearfulness is a key proximate factor determining the nonrandom order repeatedly reported for baboon troops progressing from one location to another. According to this hypothesis, the most vulnerable troop members, the walking immatures, are expected in most circumstances to be cautious and to keep others between themselves and potential danger. The more confident adults, especially large powerful males, should tend toward the front and rear of progressing troops. The fear hypothesis predicts that in progressions toward a fear source, adult males should be near the front of the troop; on the other hand, when the troop is retreating from a frightening or tense situation, adult males should be found more toward the rear. Progressions of chacma baboons away from the location of a severe fright or in retreat from another troop were compared with other progressions. Adult males tended to be more rearward in these situations. The number of adults of either sex interposed between a fear source and the first walking immature was greater for retreating troops than for others. Some adult males continued to be near the front of the troop when retreating from tense situations.     

Socio-sexual factors of troop fission in wild Japanese monkeys (Macaca fuscata yakui) on Yakushima Island,Japan

The troop fissions which occurred in a wild population of Japanese monkeys (Macaca fuscata yakui) were observed from 1977 to 1979 on Yakushima Island. The fissions were initiated in the breeding season by non-troop males who established a consort relation with estrous females. In order to analyze the socio-sexual factors which accelerated the fissions, the male emigrations and immigrations before and after two successive fissions, and the copulation frequencies, competition among males and preferences of mating partners in both sexes in the 1977–78 breeding season after the first fission were examined. The results indicated that three factors (a large number of non-troop males, a shortage of troop males and the females' choice of mating partners) effectively influenced on the establishment of consort relationships between non-troop males and estrous females. It is suggested that these factors may exert different effects on the troop disorganization in relation to troop size. In small-sized troops, a large number of non-troop males and a shortage of troop males may lead to stronger competition between them, and the females' choice affected by prolonged intimate relations with the dominant TMs may reduce their priority of access to estrous females. This situation possibly stimulates fission or male emigration in small-sized troops under the natural conditions on Yakushima Island. In contrast, in large-sized troops under isolated conditions, a surplus rather than a shortage of troop males may contribute to troop disorganization, as most former studies have suggested. A higher socionomic sex ratio may decrease the mating activities of subordinate troop males and increase the competition among them. This situation possibly accelerates the fission of large-sized troops through prolonged interactions between females and subordinate or peripheral troop males. A lower ratio and the females' choice, however, raise the mating chances of subordinate troop males and may not promote the fission of large-sized troops under isolated conditions. This study was financed in part by a Grant-in-Aid for Special Project Research on Biological Aspects of Optimal Strategy and Social Structure from the Japan Ministry of Education, Science and Culture, and by the Cooperative Research Fund of the Primate Research Institute, Kyoto University.     

Effects of vegetation type on habitat use by crop-raiding Japanese macaques during a food-scarce season

Habitat use by crop-raiding Japanese macaques (Macaca fuscata) was studied in western Japan from December 2005 to February 2006, a food-scarce season. To examine how different vegetation types affect habitat use by monkeys, two crop-raiding troops were compared: the first troop inhabited a habitat involving more wild food resources; the second troop inhabited a habitat providing fewer wild food resources. It was hypothesized that monkeys living in the habitat with fewer wild food resources are more likely to utilize human settlements and areas around them (i.e. adjacent zones), with a dependence on crop foods. Comparisons of observed and expected habitat use frequencies showed that the first troop selected evergreen broad-leaved forests and conifer plantations, and avoided adjacent zones, rice fields, and golf courses. The second troop selected adjacent zones and avoided conifer plantations, pine forests, and deciduous broad-leaved forests. Both troops moved rapidly in avoided habitat types. These results suggest that monkeys living in the habitat with fewer wild food resources are more likely to utilize areas around human settlements during a food-scarce season.     

Comparative study of grooming relationships among wild Japanese macaques in Kinkazan A troop and Yakushima M troop

The influences of socionomic sex ratio (SSR; adult males/adult female) and troop size upon male-male, female-female, and male-female grooming relationships were examined and compared between two wild Japanese macaque troops (Kinkazan A and Yakushima M troops) in Japan. The Yakushima M troop was smaller and had a higher-SSR than the Kinkazan A troop. Between the troops, (1) the male-male grooming frequency and number of partners were greater in the Yakushima M troop than in the Kinkazan A troop; (2) the female-female grooming frequency and number of partners were not different; and (3) the male-female grooming frequency and number of partners were not different. Based on these features, the patterns of female-female and male-female grooming relationships appear to be independent of SSR and troop size variations. In contrast, male-male grooming relationships are influenced by both factors, especially SSR. Frequent grooming interactions among males may be useful for the continued coexistence of relatively many males especially in a higher-SSR troop.     

Intermale relations and troop male membership changes in langurs (Presbytis entellus) in Nepal

Data on intermale social relations and troop membership changes in one Nepalese high-altitude population of free-ranging langurs (Presbytis entellus)are reported here. Data were collected from six troops by three observers and cover 32 months of observations. The predominantly multi-male troops indicate an alternating pattern of exclusions and introductions with gradual adult male replacement. Takeovers and infant killing were not observed. Analysis of adult social behavior records show qualitative and quantitative differences in intrasexual relations, with primarily agonistic social contacts occurring between males. Agonistic encounters between females and between males differ in frequency of occurrence, types of be-haviors used, cause, and consistency in direction of threats between individuals. Individual adult male frequency of interaction with females and immatures varied significantly, with the majority of these interactions occurring between the dominant troop male and other troop members. Data indicate that intermale dominance is a major factor in determining male access to fertile females: This appears to be achieved by either directly excluding males from the troop or effectively “controlling” their inter-actions with troop females. Data from these studies are compared with data from other Presbytis entellusinvestigations. Review of these data suggests that intraspecific variability in intermale social dynamics and type of troop male membership change are correlated with the percentage of nontroop males. It is suggested that environmental pressures resulting in social crowding can be critical in determing the occurrence of takeovers in some populations of Presbytis entellus.     

Ecology and behavior ofPresbytis thomasi in Northern Sumatra

A field study of 23 bisexual troops, ranging in size from 3 to 21 members ( =8), and two all-male groups of the Thomas's leaf monkey (Presbytis thomasi) was conducted in North Sumatra from November 1981 to April 1984. Most troops (N=19 or 82.6%) contained only one adult male. Two troops and one group were most intensively studied. The home range was 12.3–15.7 ha for the two bisexual troops, and only 1.7 ha for the one, all-male, ten-member group. Fruits composed more than 50% of their diets. Vocalizations were classified into 13 types. Births occurred at any time of the year. Among three males of a bisexual troop, serious fights were observed: two males died of wounds and the former beta male became the new alpha male. After this social change, the home range area of this troop gradually shifted eastward. But, 3.5 months after the social change, a 9-month-old infant male stayed alone in the western part of its former range. Thereafter, he became a solitary male and sometimes went into the riverine area of the Bohorok river. The occurrence of male replacement suggests instability of multi-male organization in bisexual troops. Moreover, the different mortality rate between males and females and the unequal sex ratios forced by the formation of one-male troops, maintained high tension levels among males competing on females.     

Ecology and behavior of the wild proboscis monkey,Nasalis larvatus (Wurmb), in Sabah,Malaysia

Proboscis monkeys,Nasalis larvatus (Wurmb), were investigated in the Padas Bay and Kinabatangan River areas, Sabah, from July 1968 to March 1969. The proboscis monkey is a common, widely distributed species of coloboids in Sabah, living in the various vegetations that extend from the coastal swamp to the inland plain. It appears to have a terrestrial tendency, compared with other coloboids, moving around on the ground in the forest and extending its activity, sometimes, to the open land along the river beach. The number of monkey in a troop, we observed, ranged from 11 to 32, and almost all troops were composed of several adult males, many more adult females, and immature animals. The adult males appear to play the role of leaders in the troop through their characteristic behavior, attacking, threatening, warning, watching, etc., other troop members or invaders. Each troop always emitted various boisterous vocalizations which were divided into 14 types.     

Breeding behaviors in the black howler monkey (Alouatta pigra) of belize

Adulterous breeding between a female howling monkey (Alouatta pigra) of one troop with a male of an adjacent troop occurred despite territorial defense between the two troops. The specific behaviors are described as well as a synopsis of daily events which occurred between the female and two males from adjacent troops. A discussion of how this interaction and the behavior patterns relate to what is known about breeding in howler monkeys and related species follows.     

The variable social organization of hanuman langurs(Presbytis entellus), infanticide,and the monopolization of females

Data from 24 wild populations of hanuman langurs (Presbytis entellus)in south Asia are used to test hypotheses seeking to explain variation in troop structure and the incidence of infanticide. The occurrence of infanticide is associated with a one-male troop structure and not with a high density. The density, predation, and economic-advantage hypotheses, as explanations for the occurrence of one-male and multimale troops, are not supported by the review. However, the monopolization hypothesis is not contradicted; the number of adult males per troop is significantly correlated with troop size and with the number of adult females per troop. Therefore it is suggested that a one-male troop structure will arise if a male is able to monopolize a group of females, a multimale troop if he cannot. One-male troops may predispose to infanticide because of high variance in male mating success and high intermale competition between groups rather than within troops. If female dispersion determines troop structure, it is speculated that females could manipulate males to form a multimale society if the advantages in terms of infant survival and intertroop conflict exceeded the costs in terms of not producing infanticidal “sexy sons.”     

Survey of the black howler monkey,<Emphasis Type="Italic">Alouatta pigra</Emphasis>, population at the Mayan site of Palenque,Chiapas, Mexico

A survey of the population of the black howler monkey (Alouatta pigra) present at the Mayan site of Palenque was conducted during 2000. A total of 911 man/hours, spread over 112 days were spent surveying the 600 ha area of pristine forest at the site for howler troops. We detected the presence of 136 individuals of which 131 were members of 20 troops, the rest were 3 solitary adult males and 2 adult males travelling as a pair. Ecological density was estimated at 23 individuals/km². Mean troop size was 7.0 individuals and it ranged from 2–12 individuals; 60% of the troops were multimale. All sighting of howler monkeys were in evergreen rain forest and 75% were in trees ≥20 m in height. The reported densities and mean troop size are higher than those reported for the species in Guatemala and in central Quintana Roo, Mexico. The vegetation of the forest contains tree species reported to be used by species ofAlouatta in the Moraceae, Sapotaceae, Leguminosae, and Lauraceae plant families. Protection of a large perimeter area (ca 1700 ha) around the archeological site by the Mexican government ensures the conservation of the forest and of the black howler monkey population present at the site.     

Who is Responsible for Fission in a Free-ranging Troop of Baboons?

The study troop of chacma baboons (Papio cynocephalus ursinus) at Mkuzi Game Reserve, Zululand, South-Africa, comprised of about 76 members that split into two new troops. The events leading to this troop fission will be described and its possible causes will be discussed. Troop fission among baboons is generally attributed to the withdrawal of low-ranking females from the main group, as a result of the cost of food competition and its effect on their reproductive success. At Mkuzi, no evidence for food competition among females was recorded in terms of rank-related time spent feeding or other time—budget components, feeding-bout length, diet composition or context of female aggression. Moreover, no evidence for rank-related differential reproductive success was found in terms of inter-birth intervals or infant survival. Female mortality was, however, related to dominance rank, with circumstantial evidence suggesting that cause of mortality was predation by leopards. Rate of female disappearances, aggression levels among females, and the percentage of time they spent in proximity to other adult troop members increased after fission. Relatively short inter-birth intervals and extremely low infant mortality rate at Mkuzi resulted in a small number of receptive females at any one time, and therefore in high costs of male sexual competition as expressed in the high levels of male aggression and woundings, both reduced after fission. It is suggested that this troop fission may have been initiated by the resident males, triggered by the high cost of sexual competition, and forced on the females, who were, consequently, subjected to higher risk of predation. The troop fission was preceded by a long process of increasing tendency for sub-trooping. It was initiated by the four resident males who kept a large distance apart from each other, herded oestrous female associates away from others and were followed by other females. The females generally tended to stay close to associates, males and females. These parties were followed by the peripheral and immigrant males who had no female associates, and eventually two distinct daughter troops were formed.     

Consortship and Mating Success in Chacma Baboons (Papio cynocephalus ursinus)

Chacma baboons (Papio cynocephalus ursinus) show a lower consortship take‐over rate and longer consortship duration than the other savannah baboons ( Bulger 1993 ). It has been argued that researchers have focused on atypically small troops with few adult males, resulting in low competition for access to oestrous females. Consortship data from two mountain baboon troops containing seven and four males, respectively, were analysed to determine whether the troop with the greater number of males showed a weaker correlation between mating success and rank due to an expected higher consortship take‐over rate. No consort take‐overs were observed in either study troop and mating success in both troops was correlated strongly with male rank. The distribution of days spent in consortship amongst the males could be explained by the priority‐of‐access‐model. The degree of cycle overlap determined the number of males observed consorting oestrous females, whereas the number of males did not influence the relationship between rank and consorting activity.     

Correlates of patterns of range use of a troop of yellow baboons (Papio cynocephalus). I. Sleeping sites,impregnable females,births, and male emigrations and immigrations

A free-ranging troop of 108 to 130 yellow baboons (Papio cynocephalus) was sampled systematically for 1596 h. Seasonal variations in the area of the range of the troop, and the degree to which the patterns of range use of the troop were clumped in space are found to be correlated with (1) diversity of use of sleeping sites, (2) time of departure from sleeping trees, (3) number of impregnable females in the troop, and (4) number of emigrations from, and immigrations into the troop by adult males. The reproductive strategies of troop members, especially those of impregnable females, are suggested to influence patterns of range use. Some effects of the presence of observers on the troop are measured and discussed.     

Experimental field study of the relative costs and benefits to wild tamarins (Saguinus imperator and S. fuscicollis) of exploiting contestable food patches as single- and mixed-species troops

Several species of tamarins form stable mixed-species troops in which groups of each species feed, forage, rest, and travel together during much of the year. Although the precise set of factors that facilitate this ecological relationship remains unclear, predator detection and foraging benefits are presumed to play a critical role in maintaining troop stability. In this work we present data from an experimental field study designed to examine how factors such as social dominance and within-patch foraging decisions affect the costs and benefits to tamarins of visiting feeding sites as single- and mixed-species troops. Our data indicate that when they exploited contestable food patches (sets of eight feeding platforms, two of which contained a 100-g banana), each tamarin species experienced foraging costs when they arrived as part of a mixed-species troop. These costs were found to be less severe for emperor tamarins because they were socially dominant to saddle-back tamarins and could displace them at feeding sites. We conclude that the foraging benefits to tamarins residing in mixed-species troops are asymmetrical, and that at feeding sites in which the amount of food in a patch is insufficient to satiate all troop members, even minor differences in the timing of return to food patches and changes in troop cohesion have a measurable effect on the costs and benefits to participating tamarin species.     

Five natural troops of Japanese monkeys on Shodoshima Island: II. A comparison of social structure

The results of a comparative study of five natural troops of Japanese monkeys living on Shodoshima Island are as follows. (1) When troops were feeding at the feeding places, various cases, such as individuals spaced out dispersively or close by in a gregarious state, were observed. (2) Differences were also observed among the troops at the feeding place; some troops always fed in a dispersive state, on the whole, while others fed in a gregarious state with small distances between individuals. (3) Differences of social structure were observed among the five troops: differences of the number of classes and sub-classes in males and females, of the relation between classes and their age distribution in males, of the proportion of individuals who intruded into the central part of the troop or who made it their core area of activity to the total male population, etc., and it was also assumed that some troops were integrated more strictly, while others were integrated loosely. (4) These differences of social structure among the troops were assumed to be closely related to the gregariousness or dispersiveness of the each troop at feeding time. From these facts several decisive factors of social structure were considered.     

Intertroop Transfer and Dominance Rank Structure of Nonnatal Male Japanese Macaques in Yakushima, Japan

We examined the interaction between intertroop transfer and male dominance ranks in a wild population of Japanese macaques (Macaca fuscata yakui) in Yakushima using data collected over 15 years. Intertroop transfer tended to maintain a linear, stable, and age-graded dominance rank order among nonnatal males irrespective of variation in troop size or composition. All males that joined a troop at the top of the rank order were prime adults. Among males joining at lower ranks, entry at the most subordinate position in the hierarchy was common. Males joining at lower ranks tended to join troops in which all other resident males were the same age or older. Adult males tended to join troops with few or no males. Young males tended to join troops with many resident males, and in which a relatively large proportion of males was other young ones. Intertroop transfer was responsible for most rank changes of resident males. The most common cause of males rising in rank was the emigration or death of a higher-ranking male. Males fell in rank most frequently as a result of a new male joining the troop at the top of the hierarchy. Rank reversals among resident males were rare. The cumulative effects of male transfers produce sociodemographic variation within a troop over time and sociodemographic diversity among troops in a local population. A key feature of intertroop diversity is that larger troops have a significantly greater proportion of young males than smaller troops. This diversity also creates the potential for intertroop variation in the severity of male competition and provides a range of options for transferring males.     

Long distance mobility of male Japanese macaques evidenced by mitochondrial DNA

A 487-nucleotide sequence in the polymorphic D-loop region of matrilineally inherited mitochondrial DNA was compared in samples from 14 (9 adult males and 5 females or young) Japanese macaques (Macaca fuscata fuscata) of two troops at Gagyusan in Takahashi City, Okayama Prefecture, Japan. The majority (7 out of the sampled 9) of the adult males associated with the troops had nucleotide sequences of six distinct types, all of which were different from that of the Gagyusan troop females, whereas two young solitary males shared the same sequence. The present study exemplified a case in which the majority of adult males immigrated from outside the local population. Notably, two of the males were revealed to share the same sequence determined for a matriline 45 km away. Electronic Publication