A contribution to tropical rain forest taphonomy: retrieval and documentation of chimpanzee remains from Kibale Forest, Uganda

The absence of Pan and Gorilla fossils from Africa has led some to suggest that African rain forests are not conducive to bone preservation. The absence of fossils is unfortunate as it hampers phylogenetic and socioecological interpretations on the divergence of the earliest hominids. For the most part, taphonomic studies have been restricted to cave and open country contexts. With this in mind, we have initiated a taphonomic project in a tropical rain forest, the Kibale Forest of western Uganda. In the course of bone gathering activities over the past 4 years, we have documented the retrieval of skeletal remains representing nine chimpanzees (Pan troglodytes schweinfurthii). Crania and mandibles are most commonly recovered, followed by elements of the axial skeleton, and finally, appendages. Vertical segregation of small compact bones can occur in areas with a soft substrate. Scavenging activity suggests the role of suids, but this has not been proven. Geochemical tests suggest that Kibale soils are neutral and may be conducive to bone preservation. Our independent preliminary data from bone weathering/survival experiments indicate that bones appear undamaged after several years and are able to accumulate on the forest floor. These results contrast with popular assumptions on the potential of African rain forests as potential fossil reservoirs.     

Analysis of geophagy soils in Kibale Forest, Uganda

Four soil samples from the Kibale Forest, Uganda, representative of material regularly ingested by chimpanzees, were studied for their mineral, chemical, and geochemical composition. These geophagy soils have a high content of metahalloysite, a partially hydrated clay mineral that may act much like the pharmaceutical Kaopectate™. Among the elements that may act as a stimulus or stimuli for geophagy behavior, only iron is very high (total iron ranges from 6% to 17%); other possibilities such as calcium, chromium, cobalt, bromine, and iodine are either relatively low or are below their detection limits. Chlorine is below detection limits which eliminates sodium chloride as a possible stimulus. Depending on relative availability in the gut, iron offers the most likely chemical stimulus for geophagy and given the mineral composition of the samples, metahalloysite is the most likely mineral stimulus. Iron may play a role in replenishing hemoglobin which would be important in chimpanzee physiology at high elevations near the flanks of the Ruwenzori Mountains. Metahalloysite, which in this case exists in a relatively pure crystalline form, may well act to quell symptoms of diarrhea and act similarly to Kaopectate™. Organic chemical analyses indicate only traces of organic matter and no humic acids in the K14-E14 sample.     

Censusing chimpanzees in the Budongo Forest,Uganda

It is difficult to make valid comparisons of chimpanzee densities among sites because observers calculate them using different methods. We argue that nest count estimates of density are preferable to densities from home range estimates because of the problems of defining home range. There are many problems associated with nest count methods, some of which have not been addressed in previous studies. In 1992, we censused chimpanzees in the Budongo Forest using three methods;the standing crop nest count (SCNC), the marked nest count (MNC), and visual sightings of the animals (VS). Each method is based on standard line transect techniques. Of 96 nests monitored for decay rate,those constructed in the dry seasons decayed faster than those in the wet seasons. All- day follows of individual chimpanzees and observations of nesting chimpanzees at dusk showed that about 15.8% of night nests were reused,17.5% of the population did not build nests, and 18.8% of nests were first constructed as day nests. Given the variability in nest decay rates, we argue that MNC is a better method than SCNC because it avoids having to calculate decay rates.     

Infanticide and cannibalism by male chimpanzees at Ngogo, Kibale National Park, Uganda

Researchers have documented infanticide by adult males in four wild chimpanzee populations. Males in three of these have killed infants from outside of their own communities, but most infanticides, including one from Kanyawara, in Kibale National Park, Uganda, took place within communities. Here we report two new cases of infanticide by male chimpanzees at a second Kibale site, Ngogo, where the recently habituated chimpanzee community is the largest yet known. Both infanticides happended during boundary patrols, which occur at a high frequency there. Patrolling males attacked solitary females who were unable to defend their infants successfully. The victims were almost certainly not members of the Ngogo community. Males cannibalized both infants and completely consumed their carcasses. These observations show that infanticide by males is widespread in the Kibale population and that between-community infanticide also happens there. We discuss our observations in the context of the sexual selection hypothesis and other proposed explanations for infanticide by male chimpanzees. The observations support the arguments that infanticide has been an important selective force in chimpanzee social evolution and that females with dependent infants can be at great risk near range boundaries, but why male chimpanzees kill infants is still uncertain.     

Interspecific interaction of the primate groups in Kibale Forest,Uganda

An ecological survey on the influence of interspecific interaction of the primates upon the distribution of their group ranges was carried out in 100 ha of the isolated forest northern outskirts of Kibale Forest in western Uganda, Africa. The study period of 105 days was from the 12th of November, 1970 to the 24th of February, 1971, including a preliminary survey of about two months. The subjects of this study are five species of primates, i.e., black and white colobus (Colobus polykomos), red colobus (Colobus badius), red tailed monkey (Cercopithecus ascanius), blue monkey (Cercopithecus mitis), and vervet monkey (Cercopithecus aethiops), which inhabited the study area. The red colobus group is thought to be the most influential of the five in the interspecific interaction.     

Soils Consumed by Chimpanzees of the Kanyawara Community in the Kibale Forest,Uganda

We previously reported on a study of 4 soils that chimpanzees of the Kanyawara community in the Kibale National Park, Uganda consumed on a near-daily basis. We suggested that iron was a possible chemical stimulus in association with high quantities of Si:Al = 1:1-dominated clay minerals in the consumed material. To test our initial findings, we analyzed 18 samples from the same general area including 7 samples that the chimpanzees did not eat. Among the chemical elements, As, Au, Br, Ca, Cl, Dy, Mg, Ni, Sb, Sr, and I are below detection limits. Only Fe stands out as a potentially important nutritional element present in sufficient quantity to provide a physiological stimulus for chimpanzees living at high elevations near the flanks of the Ruwenzori Mountains. Along with Fe, metahalloysite is present in high amounts in these soils. In its pure crystalline form as a pharmaceutical grade clay mineral metahalloysite may well counteract the debilitating effects of diarrhea, with an effect similar to what is achieved with kaolinite (cf. Kaopectate^TM). An unexpected result, the relatively high nitrogen and carbon in the eaten samples relative to the uneaten group, indicates the chimpanzees may have a higher threshold for organic-rich material than previously believed. Contrarily, the color of the ingested material, depicts a material with less humus than in the uneaten group, a finding that is compatible with previous work reported at other geophagy sites in Africa. Of all the choices of soil available to them, the chimpanzees appear to be selecting highly homogeneous chemical natural earths with well-leached and uniform mineralogical material similar to the uneaten group, but with higher relative amounts of clay size material.     

New cases of inter-community infanticide by male chimpanzees at Ngogo,Kibale National Park,Uganda

Infanticide by males has been recorded in four chimpanzee populations, including that in Kibale National Park, Uganda. Some infanticidal attacks occur during inter-community aggression. The sexual selection hypothesis does not easily explain these attacks because they may not directly increase male mating opportunities. However, females in the attackers’ community may benefit by expanding their foraging ranges and thereby improving their reproductive success; thus infanticide may increase male reproductive success indirectly. We report two new cases of infanticide by male chimpanzees at Ngogo, Kibale National Park. Like two previous cases, these occurred during a boundary patrol and were almost certainly between-community infanticides. The patrolling males attacked despite the proximity of males from the victims’ presumed community. This probably explains why, unlike the earlier cases, they did not completely cannibalize their victims. Such attacks seem to be relatively common at Ngogo and infanticide may be an important source of infant mortality in neighboring communities. Our observations cannot resolve questions about the sexual selection hypothesis. However, they are consistent with the range expansion hypothesis: the infanticides occurred during a period of frequent encounters between communities associated with a mast fruiting event, and Ngogo community members greatly increased their use of areas near the attack site during another mast fruiting event one year later. Our observations contribute to growing evidence that lethal intergroup aggression is a common characteristic of wild chimpanzee populations.     

Social behavior of chimpanzees in the Budongo Forest,Uganda

The author studied the social organization and behavior of wild chimpanzees in the Budongo Forest, Uganda, between September, 1966, and March, 1967. A population of more than 50 chimpanzees became habituated to the author and was followed continuously, by means of individual identification, throughout the study period. The present article deals with the chimpanzee's social behavior, with special reference to social organization.The central organization which controls and maintains chimpanzee society cannot be rigid dominance rank order, since agonistic interactions among chimpanzees were not frequent. On the other hand, friendly or associative social behavior was frequently observed, some of which was unique in non-human primates. Greeting behavior, especially, and begging-and-food-sharing behavior show the existence of the chimpanzee's unique communicative system, which is backed by symbolic function. This kind of communicative system appears to have an important role in the maintenance of the unique social organization of chimpanzees, which has a loose regional integration, though the animals frequently gather into parties and later split up.Sexual activity was observed throughout the study period, but the peak was seen between December and February, during the dry season.The field work necessary for this study was carried out as a part of the Kyoto University Africa Primatological Expedition and was financed mainly by a Grant for Scientific Research from the Ministry of Education and partially by the Wenner-Gren Foundation for Anthropological Research and by the economic world of Japan.     

Variation in diet and ranging of black and white colobus monkeys in Kibale National Park,Uganda

Recently, considerable intraspecific variation in the diets and ranging behavior of colobine monkeys has been described, although in most cases this has involved documenting variation between, not within, sites. Some African colobines, such as guerezas (Colobus guereza), are relatively abundant in disturbed habitats that are very heterogeneous, raising the intriguing possibility that even groups with overlapping home ranges may exhibit large behavioral differences. If such differences occur, it will be important to understand what temporal and spatial scales adequately portray a species’ or population’s diet and ranging behavior. This study documents within-site variation in the diet and ranging behavior of guerezas in the habitat types in which they are described to be most successful—forest edge and regenerating forest. We collected data on eight groups of guerezas with overlapping home ranges for 3–5 months each in Kibale National Park, Uganda. The guerezas were highly folivorous, with leaves constituting 78.5–94.0% of the groups’ diets. The percentage of mature leaves and fruit in the diet varied widely among and within groups. We show that differences among groups in the intensity with which they fed on specific tree species were not just related to phenology, but also to differences in the forest compositions of groups’ core areas. Range size estimates varied more than fivefold among groups and the minimum distance from groups’ core areas to eucalyptus forest (which all groups regularly fed in) was a better predictor of range size than was group size. These results reveal considerable variation in the diet and ranging behavior among groups with overlapping ranges and have implications for comparative studies, investigations of within- and between-group feeding competition, and the potential for populations to adapt to anthropogenic or natural environmental change.     

Social organization of chimpanzees in the Budongo Forest,Uganda

A population of wild chimpanzees in the Budongo Forest, Uganda, was studied between September, 1966, and March, 1967, by means of habituation and identification of each individual. This article deals with the grouping patterns, social units, and social organization of the chimpanzees in their natural habitat. Although parties of chimpanzees form groups of many patterns according to each particular situation and have no permanent membership, many chimpanzees live within a certain restricted area and gather to form parties consisting, in the main, of chimpanzees acquainted with each other. More than 50 individuals combined by social bonds in a loose regional population which is separated from other populations without recourse to geographical or physical barriers, though it maintains friendly contact with neighboring chimpanzee residents and with strangers. No particular individual group leader can be found, but any adult, especially a male, may act as a nucleus of each party.This study was carried out as a part of the Kyoto University Africa Primatological Expedition; the field work was financed mainly by a Grant for Scientific Research, Ministry of Education, and in part by the Wenner-Gren Foundation for Anthropological Research and by the economic world of Japan.     

Coping with Forest Fragmentation: The Primates of Kibale National Park,Uganda

A goal of conservation biology is to determine which types of species are most susceptible to habitat disturbance and which types of disturbed habitats can support particular species. We studied 20 forest fragments outside of Kibale National Park, Uganda, to address this question. At each patch, we determined the presence of primate species, tree species composition, patch size, and distance to nearest patch. We collected demographic, behavioral, and dietary data for Abyssinian black-and-white colobus (Colobus guereza). Black-and-white colobus and red-tailed guenons (Cercopithecus ascanius) were in almost all fragments; Pennant's red colobus (Procolobus pennantii) and chimpanzees (Pan troglodytes) were in some fragments; and blue monkeys (Cercopithecus mitis) and gray-cheeked mangabeys (Lophocebus albigena) were absent from all fragments. No species characteristics—home range, body size, group size, or degree of frugivory—predicted the ability of species to live in patches. No characteristics of patches—area, distance to the nearest patch, distance to Kibale, or number of food trees present—predicted the presence of a particular species in a patch, but distance to Kibale may have influenced presence of red colobus. Black-and-white colobus group size was significantly smaller in the forest patches than in the continuous forest of Kibale. For a group of black-and-white colobus in one patch, food plant species and home range size were very different from those of a group within Kibale. However, their activity budget and plant parts eaten were quite similar to those of the Kibale group. The lack of strong predictive variables as well as differences between other studies of fragmentation and ours caution against making generalizations about primate responses to fragmentation.     

The diet of chimpanzees in the Budongo Forest Reserve, Uganda

Chimpanzee diets are highly variable, but in all cases dominated by ripe fruit. Previous work has suggested that in the Budongo Forest Reserve, Uganda, ripe fruit remains available throughout the year, but dietary data for chimpanzees at this site remain sparse. This paper details the diet of a recently habituated community of Budongo chimpanzees living in the Sonso region. Chimpanzees of this community spent 64.5% of their feeding time eating fruit, and 19.7% eating arboreal leaves. Terrestrial herbaceous vegetation formed only a minor component of the diet. In these general dietary characteristics, Budongo chimpanzees show greater similarity to those of the Gombe National Park than they do to those in the geographically closer and floristically more similar Kibale Forest National Park. The diet was dominated by the fruit of four species and leaves of two species, although the composition of the diet varied from month to month, remaining diverse. Figs were consumed throughout much of the year, and in consequence, should perhaps be regarded as a staple, rather than fallback, food. A period of food scarcity was not apparent in this study and future comparative nutritional investigation will be required to determine whether these chimpanzees face a time of dietary hardship.     

Ranging Patterns of the Mangabey,Cercocebus albigena,in the Kibale Forest,Uganda1

Im Reservat des Kibale Forest in Uganda wurden im Mai—Juni 1971 die täglichen Marschrouten und räumlichen Zerstreuungen einer freilaufenden Gruppe von Cercocebus albigena untersucht. Die räumliche Organisation dieser Gruppe unterschied sich in mehreren Hinsichten von der anderer Regenwaldaffen. Während diese zum Beispiel in ziemlich engen Gebieten leben, bewohnt diese Cercocebus-Gruppe mehr als 34 ha, also ähnlich viel wie Bewohner der offenen Steppe. Ebenso entsprachen die täglichen Marschrouten und die mittlere Entfernung zwischen den Mitgliedern dieser Gruppe eher denen der am Boden in offener Landschaft lebenden Affen. Diese Ergebnisse zeigen, daß sich baumlebende Regenwaldbewohner in Wohngebietsgröße, täglichen Wanderungen und Gruppendichte beträchtlich unterscheiden. Theorien oder Verallgemeinerungen, daß die soziale Organisation waldlebender Arten weniger veränderlich sei als die von offener Landschaft, müssen erneut durchdacht werden.     

Forest association and phenology of wild coffee in Kibale National Park, Uganda

A study on the forest association and phenology of wild coffee ( Coffea canephora Pierre) was conducted in Kibale forest, Uganda. Nested quadrats were used to enumerate tree species, including coffee and herbaceous plants associated with forest and coffee stands. A total of 150 coffee trees was marked along transects and monthly scans carried out to score for fruits, flowers, leaves and leaf insect damage. Pre- and post-dispersal predation levels and coffee yield estimates were made by examining fruits from trees, forest floor and seasonal fruit falls into demarcated plots. In the forest, wild coffee stands are associated with low-quality forest types in terms of timber species (about 10.5 canopy species/study site) and low stocking densities of trees ≥ 50 cm d.b.h. (average 38 trees ha⁻¹ for each site) and poor forest regeneration. In the forest, wild coffee reproductive phases overlap with ripening, coinciding with flower bud and flower production. The variable peak ripening season falls between November and April. The wild coffee yields are generally low (average of 3.5 intact fruits 16 m⁻² month⁻¹), with low insect fruit/seed damage (4–19%) but high levels of wastage due to monkeys, bats and birds.