Mahale Mountains National Park Research Articles

Assessing Relationship Quality and Social Anxiety Among Wild Chimpanzees Using Self-Directed Behaviour

Current theory on primate social relationships implies that relationship quality consists of three factors: value, security, and compatibility. The relationship security of each group member can be determined using the level of social anxiety found when that individual is in the proximity of other individuals. I studied social anxiety by measuring the rate of rough selfscratching behaviour (RSS), a self-directed behaviour, in wild chimpanzees in Mahale Mountains National Park, Tanzania. The RSS rate drastically differed across individual activities; RSS was rare when the focal individual was foraging or moving, but frequent during resting. The male RSS rate while resting was inversely correlated with dominance rank, particularly when males were with other group members; higher-ranking males performed RSS less often than lower-ranking males. The RSS frequency of males did not vary with the proximity of group members or the association level of the individuals in proximity. In contrast, close proximity of group members increased the female RSS rate. In addition, females performed RSS more frequently when a non-affiliative group member was in their proximity than with an affiliative group member. The relative dominance rank of the individuals in close proximity did not affect the RSS rate in either males or females. Furthermore, infant contact or separation from the mother did not influence the maternal RSS rate. These results suggest that anxietyinducing situations differ between sexes in this species, and that for female chimpanzees, relationship security is related to association level. The results are discussed in terms of interspecific variation in social dominance style and inter-individual tolerance within primates.

<Forum> Chimpanzee viewing and regulation: Mahale Mountains National Park

<Forum> Chimpanzee viewing and regulation: Mahale Mountains National Park

Incident of intense aggression by chimpanzees against an infant from another group in Mahale Mountains National Park, Tanzania

We document here an unusual case of intense aggression against an infant male from another group by chimpanzees (Pan troglodytes schweinfurthii) of the Mahale Mountains National Park, in Tanzania. Adult males of the study group collectively attacked an unknown male infant. Although an unknown female, probably the mother, tried to retrieve him, the infant was seriously injured and most likely died. During this incident, the unknown female attacked and injured two researchers. After the aggressive encounter, it was found that six of the nine adult males in the study group were wounded. Attacking the extragroup male infant may have the effect of weakening the future power of the neighboring group, leading to better access to resources and enhanced safety in the future for the study group.

Possible control of Senna spectabilis (Caesalpiniaceae), an invasive tree in Mahale Mountains National Park, Tanzania

Senna spectabilis is a tree native to South and Central America. Thirty-five years ago it invaded the Mahale Mountains National Park in western Tanzania where it presently covers c. 225 ha. We quantified its occurrence relative to that of sympatric species of native trees, and compared girdling and felling as methods for its control in three 0.25 ha plots. Within invaded areas of forest this exotic species was both the most abundant and dominant of the 26 species of tree recorded. During 4 years of monitoring the experimental plots the abundance of S. spectabilis declined markedly in the plots where control methods were practised, but increased slightly in the unmanipulated plot. In contrast, the abundance of native tree species increased markedly in the plots where S. spectabilis had been removed or killed, with higher densities in the girdled rather than the felled plot. S. spectabilis appears to suppress the recruitment of native trees in the Park, and its removal can encourage regeneration of the degraded forest without the need for artificial seeding.

Leaf Processing by Wild Chimpanzees: Physically Defended Leaves Reveal Complex Manual Skills

AbstractThe manual processing of eight species of leaf was investigated in the M‐group chimpanzees of Mahale Mountains National Park, Tanzania. Leaf species varied in the extent to which physical defences made consumption difficult. In all, 96 distinct techniques for leaf processing were identified, but two species with defended leaves (Ficus asperifolia and F. exasperata) required 2.5 as many techniques as did any of the six undefended species. Moreover, chimpanzees made more multiple leaf detachments, and made more subsequent modifications of the leaves, when dealing with the leaves of these two Ficus species, compared with the undefended leaf species. This greater complexity was associated with evidence of flexible, hierarchical organization of the process: iteration of modules consisting of several processing elements, facultative omission of modules, or substitutions of alternative modules. Comparison with data from mountain gorillas is made, and is consistent with similar cognitive architecture in the two species. We consider that, not only is hierarchical organization currently associated with mechanical difficulty in food processing, but that over evolutionary time‐scales difficulties in food processing may have selected for cognitive advance.

Behavioral seasonality in Mahale chimpanzees.

To analyze how the chimpanzees in the Mahale Mountains National Park, Tanzania, change their grouping pattern, activity budget, travel speed, and travel distance within an annual cycle, I divided 1-year data into four periods. The Mahale chimpanzees have the behavioral flexibility to adapt to various climates and exhibited at least three behavioral seasons. In the early wet season, chimpanzees formed a few, large parties, and spent much time feeding on insects and animal meat. In the early and late dry seasons, chimpanzees maintained party sizes as large as in the early wet season, and traveled distances similar to the early wet season, but spent the most time feeding and traveling within the year. By contrast, in the late wet season chimpanzee parties broke up into more numerous, small groups, and traveled slowly over shorter distances. Although time spent feeding and traveling were the same as that in the early wet season, time spent feeding on terrestrial herbaceous vegetation (THV) was the highest in the year. The results suggest that chimpanzees travel longer, faster, and farther in seasons when they form large parties.

Leaf-grooming by a wild chimpanzee in Mahale.

During the course of systematic observations of the leaf-grooming behavior by the chimpanzees (Pan troglodytes) of the Mahale Mountains National Park, Tanzania, I recovered a louse from a leaf "groomed" by an adult male chimpanzee after a typical leaf-grooming session. During the leaf-grooming session I observed a small object on his lower lip. He picked up a leaf, transferred the small object from his lip to the leaf, folded the leaf and crushed the folded side of the leaf with his thumb. I present this observation as further evidence of the "squashing ectoparasites" hypothesis for leaf-grooming.

The Four Chimpanzee Skulls Collected in the Mahale Mountains, Tanzania.

Morphological and osteological data taken from chimpanzee skeletal materials gathered at chimpanzee research sites are accompanied by life history data (e.g. diet, environment of habitat, sexual activity and social relationship). Unfortunately morphological and osteological studies of chimpanzee skeletal remains from long-term field research projects are rare (Yasui and Takahata, 1983, an infant of P. t. schweinfurthii from Mahale mountains National Park, Tanzania; Morbeck and Zihlman, 1989, ten individuals of P. t. schweinfurthii from Gombe National Park, Tanzania; Matsuzawa et al. 1990, a young male of P. t. verus from Bossou, Guinea). This study described basic morphological and osteological information (i.e. linear measurements of skulls and dentitions, dental wear, notable pathological traits) taken from four free-ranging chimpanzee skulls (Pan troglodytes schweinfurthii) that were collected from the Mahale Mountains National Park, Tanzania. The dental wear is then discussed in relation to the life history variables of individual chimpanzees.

An attempted within-group infanticide in wild chimpanzees

Two high-ranking adult male chimpanzees (Pan troglodytes) of M group in the Mahale Mountains National Park, Tanzania, tried to get a newborn female infant of an adult female who was born in M group. The mother was not seen to mate with these adult males during the probable conception cycle of the infant, but she disappeared from the group during the later cycle, when she may have been inseminated by a male of one of the neighboring unit groups. The adult males failed to get the infant because the grandmother of the newborn and her female friend cooperated to protect the mother and infant from attacks by the males. The sexual selection hypothesis for infanticide by adult male chimpanzees holds for this observed case. The sudden disappearance of another infant, a healthy female, strongly suggests the killing of female infants too. Therefore, the asserted male-biased infanticide in chimpanzees appears to be less tenable.

Activity budgets of wild female chimpanzees in different reproductive states

Activity budgets of wild female chimpanzees (Pan troglodytes schweinfurthii) when lactating were compared with those during estrus and anestrus. Five anestrous females, seven estrous females, and three lactating females in Mahale Mountains National Park, Tanzania, were the subject of focal sampling. Time spent for feeding, resting, and moving was examined. For each of these three categories of activity, there was no significant difference of time spent for each activity between lactating females and either estrous or anestrous females. The females spent about 30% of their daytime feeding, about 40% resting, and about 30% moving. One of the reasons for the lack of difference might be the type of parties that females attended when they were observed. In most cases, the females were seen in large bisexual parties. Although lactating females are expected to need more nutrition than cycling females and this might affect their activity budget, the party type they attended might also affect the budget.

Intergroup Differences in a Social Custom of Wild Chimpanzees: The Grooming Hand-Clasp of the Mahale Mountains

Intergroup Differences in a Social Custom of Wild Chimpanzees: The Grooming Hand-Clasp of the Mahale Mountains

Preliminary Study of Feeding Competition Between Baboons and Chimpanzees in the Mahale Mountains National Park, Tanzania

Of eight primates sympatric to chimpanzees (Pan troglodytes schweinfurthii) in the Mahale Mountains National Park, Tanzania, yellow baboons (Papio cynocephalus cynocephalus) are the second largest in size after chimpanzees. Baboons in Mahale have invaded the chimpanzee range over the year. Group size, range use, feeding behavior, and diet of baboons and chimpanzees were recorded during the same season to investigate the interspecific relationship. The data indicate feeding competition between the two species. Chimpanzees may be negatively affected by the competition due to their dependence on specific ripe fruits, as their dietary items significantly overlap with those of the baboons.

Social scratch: Another custom in wild chimpanzees?

Chimpanzees (Pan troglodytes schweinfurthii) in the Mahale Mountains National Park, Tanzania, scratch other individual's bodies while they groom them. This behavioral pattern of "social scratch" is another example of locality-specific social behavior, or custom, as it is not found in the Gombe National Park, Tanzania, about 150 km north of Mahale, nor has it been reported from any other sites of chimpanzee study. Frequency of social scratch was correlated with frequency of social grooming, but not with frequency of self-scratch. Frequencies of social scratch per grooming bout among adult and adoles-cent males, and from lactating females to infants or juveniles, were high, and among males, higher-ranking males especially received more. These facts indicate some social function of the behavior. Social scratch was directed mostly to the dorsal side of the body. However, when lactating females social scratched to infants or juveniles, they scratched other body parts. Social scratch was not lateralized to left or right. We present four hypotheses on the functional origin and on the learning process of this cultural behavioral pattern.

Fractal Long‐Range Correlations in Behavioural Sequences of Wild Chimpanzees: a Non‐Invasive Analytical Tool for the Evaluation of Health

Quantitative evaluation of health impairments in wild chimpanzees was explored using fractal long‐range correlations of behavioural sequences. The health status of 13 chimpanzees in the Mahale Mountains National Park, Tanzania was evaluated non‐invasively using standard behavioural observation and parasitological analysis of stool samples. Based on these data, individuals were classified as being either healthy or sick. Behavioural sequences were analysed and shown to exhibit long‐range power law correlations. The behavioural sequences of individuals in healthy and sick states were quantitatively evaluated using detrended fluctuation analysis of social and non‐social behaviours within behavioural sequences. These values were compared and significant differences in long‐range correlations were found between health states. Sex differences were also noted, with female social behaviour displaying a larger fractal dimension than male social behaviour. The fractal dimension of females declined significantly in sick individuals. This analysis of behaviour provides a new and effective non‐invasive method to record and evaluate the general state of health and related stress of animals in the wild. Possible applications of this method in captive situations include the monitoring and evaluating of stress levels over time.

Female choice in the opportunistic mating of wild chimpanzees ( Pan troglodytes schweinfurthii ) at Mahale

For female chimpanzees (Pan troglodytes schweinfurthii) in the Mahale Mountains National Park, Tanzania, the most common mating pattern is opportunistic. In such opportunistic matings, females copulated promiscuously but not randomly. This study describes female mate choice during 1-year observation of six females who exhibited regular genital-swelling cycles. During the study period, 169 opportunistic matings and four restrictive matings were recorded over the course of 51 days. As female estrus progressed, mating frequency and the number of adult male mating partners increased, although the number of potential mating partners did not change. Criteria of female choice examined were the direction and consent/rejection of courtship, proximity maintenance, and female grooming. Adult-male courtships were successful more often than those of adolescent males. During the earlier phase of estrus, females copulated rather promiscuously with many males. But during the later phase of estrus when the likelihood of conception is expected to be highest, they copulated repeatedly with high-ranking adult males. There was a positive correlation between female grooming frequency and mating frequency when the likelihood of conception was greatest. Female chimpanzees are thought to choose high-ranking males as fathers of their offspring. Moreover, female chimpanzees may adopt one or both of two mating strategies, i.e., a many-male strategy and a best-male strategy.

Chemistry, mineralogy and microbiology of termite mound soil eaten by the chimpanzees of the Mahale Mountains, Western Tanzania

Subsamples of termite mound soil used by chimpanzees for geophagy, and topsoil never ingested by them, from the forest floor in the Mahale Mountains National Park, Tanzania, were analysed to determine the possible stimulus or stimuli for geophagy. The ingested samples have a dominant clay texture equivalent to a claystone, whereas the control samples are predominantly sandy clay loam or sandy loam, which indicates that particle size plays a significant role in soil selection for this behaviour. One potential function of the clays is to bind and adsorb toxins. Although both termite mound and control samples have similar alkaloid-binding capacities, they are in every case very high, with the majority of the samples being above 80%. The clay size material (<2 μm) contains metahalloysite and halloysite, the latter a hydrated aluminosilicate (Al2Si2O4·nH2O), present in the majority of both the termite mound soil and control soil samples.Metahalloysite, one of the principal ingredients found in the pharmaceutical Kaopectate™, is used to treat minor gastric ailments in humans. The soils commonly ingested could also function as antacids, as over half had pH values between 7.2 and 8.6. The mean concentrations of the majority of elements measured were greater in the termite mound soils than in the control soils. The termite mound soils had more filamentous bacteria, whereas the control soils contained greater numbers of unicellular bacteria and fungi.

A Preliminary Report on the Impact of Chimpanzee Hunting on Mammal Populations at Mahale, Tanzania

The impact of chimpanzee hunting on populations of several mammalian species was examined by analyzing the data of population census on these mammals and the previous reports of chimpanzee hunting at the Mahale Mountains National Park, Tanzania. The annual kill rates (1.3-9.0%) of red colobus monkeys by the chimpanzees were estimated to be almost the same as the population growth rate of this species. These kill rates were equal or slightly higher than those reported from the Tai National Park, Ivory Coast, but extremely lower than those reported from the Gombe National Park, Tanzania. The impact of chimpanzee hunting on other prey mammals (redtailed monkey, blue monkey, blue duiker, bushbuck and warthog) seems to be small, because the annual kill rates of these species by the chimpanzees were estimated to be smaller than their population growth rates or the hunting frequencies on them by the chimpanzees were very low.

Mahale chimpanzees: Grouping patterns and cycling females

The social system of chimpanzees (Pan troglodytes schweinfurthii) is characterized by the fission-fusion of social groups. Several studies have reported that females are less gregarious than males. In the current study, adult female gregariousness depended on their reproductive state. Noncycling adult females (pregnant, lactating, or post reproductive) were observed in large bisexual parties less often than cycling adult females. On the other hand, cycling adult females were observed in large bisexual parties as often as males, regardless of their estrous state. More males were in parties that included cycling adult females with maximal genital swelling (estrous females) than in parties without them. Moreover, a bisexual party including more estrous females contained more males. These results suggest that large bisexual parties of chimpanzees are constructed by a dual mechanism. First, cycling adult females are attracted to parties that consist of the top ranking male and large numbers of adult and adolescent males. Second, adult and adolescent males that did not belong to parties originally are attracted by estrous females and join them. Thus, in Mahale Mountains National Park, Tanzania, bisexual parties of chimpanzees can be characterized as "parties for reproduction."

Changes in the Activity Budget of Wild Female Chimpanzees in Relation to Their Reproductive States

Activity budgets of wild female chimpanzees (Pan troglodytes schweinfurthii) in three reproductive states (estrous, anestrous, lactating) were compared with each other. Three lactating females, five anestrous females and seven estrous females in Mahale Mountains National Park, Tanzania were the subject of focal sampling and time spent for feeding, resting and moving was examined. For each of three categories of activity, there was no significant difference of time spent between each reproductive state. Those females spent about 40% of their daytime for feeding, about 30% for resting and about 40% for moving. One of the reasons of indifference might be the type of parties which females attended when they were observed. In most cases the females were seen in bisexual parties. Lactating females are expected to need more nutrition than cycling females and it might affect their activity budget. But the party type they attended might also affect the budget.

Site Report: The Mahale Mountains National Park, Tanzania

More than 30 years have passed since chimpanzee research camp was set up at the Mahale Mountains in Tanzania. Besides the continuous long-term research on chimpanzees, various research and descriptions on climate, plants, vegetation and animals have been made. In this paper, we made general descriptions about not only chimpanzees but also about other various aspects of Mahale which were obtained during the long term research and also some information for people who plan to visit Mahale. For details of chimpanzee research in Mahale, please refer to literature list in our web page (http://gorilla.zool.kyoto-u.ac.jp/ChimpHome/reference.html).