Intestinal parasites and bacteria of mountain gorillas (Gorilla beringei beringei) in Bwindi Impenetrable National Park, Uganda

A survey in 1994 examined intestinal helminths and bacterial flora of mountain gorillas (Gorilla beringei beringei) in Bwindi Impenetrable National Park, Uganda. Parasites and bacteria were identified to genus in the feces of two groups of tourist-habituated and one group of non-tourist-habituated mountain gorillas. Eggs were identified as those of an anoplocephalid cestode, and nematode eggs representative of the genera: Trichuris, Ascaris, Oesophagostomum, Strongyloides, and Trichostrongylus. This is the first report of Ascaris lumbricoides-like eggs in mountain gorillas. Fecal samples (n=76) from all groups contained helminth eggs, with strongyle eggs and anoplocephalid eggs being the most common. Salmonella and Campylobacter were found in both gorilla groups. Regular long-term non-invasive fecal monitoring of the populations of mountain gorillas is essential for the prevention and identification of potential health threats by intestinal parasites and bacteria in this highly endangered subspecies.This revised version was published online in April 2005 with corrections to the cover date of the issue.     

Intrapopulation differences in ant eating in the mountain gorillas of Bwindi Impenetrable National Park, Uganda

Variability in ant eating has been observed in several populations of eastern and western gorillas. We investigated the occurrence of ant (Dorylus sp.) eating in two groups of mountain gorillas (Gorilla beringei beringei) with overlapping home ranges within Bwindi Impenetrable National Park, Uganda from September 2001 to August 2002. We calculated the frequency of ant eating by an indirect method of analyzing fecal samples from silverbacks, adult females, and juveniles. One group consumed ants significantly more often than the other (3.3 vs 17.6% of days sampled). Furthermore, the group that consumed ants more often also consumed them on a seasonal basis (September–February monthly range: 0–8%; March–August monthly range: 30–42.9%). Finally, females and juveniles of this group consumed ants significantly more often than did the silverback (total samples containing ants: silverback, 2.1%; adult female, 13.2%; juvenile, 11.2%). Differences in ant eating between groups are likely due to variability in use of habitats where ants occur (particularly secondary forests). Surveys of ant densities in differing habitats, nutritional analysis of ants, and quantification of the amount of ants in their diets are necessary to understand if ant consumption is due to availability, nutritional value, group traditions, or taste preference.     

Capillaria hepatica (Nematoda) infections in human-habituated mountain gorillas (Gorilla gorilla beringei) of the Parc National de Volcans, Rwanda

Habituation to humans of free-ranging populations of endangered mountain gorillas (Gorilla gorilla beringei) raised concern of anthropozoonotic transmission of parasitic helminths and protozoans. Examinations of liver tissue of 19 gorillas found dead in the Parc National de Volcans, Rwanda, revealed 10 cases of hepatic nematodiasis due to Capillaria hepatica. Identifiable C. hepatica eggs were present in the liver of 4 gorillas (3 juveniles, 1 adult), and nematode cross-sections were found in 1 juvenile gorilla. Six other adult gorillas had areas of periportal and subcapsular fibrosis with calcified eggs. Histologically, the lesions surrounded by the areas of mild inflammatory reaction were characterized by subcapsular, periportal foci of fibrosis in which were embedded numerous C. hepatica eggs. Control of hepatic capillariasis in the remaining populations of mountain gorillas should be focused on eradication or control of populations of rodent pests (i.e., mice and rats) that sustain the reservoir of C. hepatica in habitats shared by gorillas and humans.     

Geophagia by mountain gorillas (Gorilla gorilla beringei) in the Virunga Mountains,Rwanda

Mountain gorillas (Gorilla gorilla beringei) occasionally eat material from weathered regolith (subsoil) sediments in the Virunga Mountains of northwestern Rwanda. The possible nutritional significance of this behaviour has been investigated by analyzing the geochemistry, primary mineral composition, and clay content of several regolith and surface soil (paleosol) samples. Iron, Na, and Br content may be important in geophagy, and clay present in the soil may also have nutritional importance.     

Observations on the ontogeny of feeding behavior in mountain gorillas (Gorilla gorilla beringei)

This report describes observations on the ontogeny of food choice in mountain gorillas (Gorilla gorilla beringei), made during a 17-month field study of mountain gorilla feeding ecology in the Parc National des Volcans, Rwanda. Data are presented on the feeding behavior of two infants observed from birth to the age of 8 months and on older infants and juveniles. This information is compared with data on the composition and diversity of the diets of young adults and adults in the same social group. Initial feeding by infants is usually synchronized with the mother's behavior: infants ingest the same food, or a different part of the same plant species, currently being eaten by the mother or just eaten by her. This suggests that observational learning is largely responsible for the transmission of food preferences. Most feeding by young infants, whether or not synchronized with the mother's, is on those foods eaten most frequently by adults. Infants also independently sample potential foods, some of which are apparently not consumed by adults. The frequency of sampling declines with age, although even adults occasionally ingest foods not observed to be eaten by other adults. By the age of 3 years, young mountain gorillas have developed the basic dietary patterns of adults, in terms of the number of foods eaten, the proportions in which specific foods are consumed, and diet diversity and equitability. There is a strong possibility that chemical cues influence food choice, but their role remains unclear.     

Observations on a small group of mountain gorillas (Gorilla gorilla beringei).

On the basis of a 5-month field study, data are presented on home range, patterns of daily movement and social behaviour in a small free-living gorilla group. Changes in group composition that occurred during the study are analysed with special reference to their effect on inter-individual distance. The relationships with other groups and lone individuals whose home ranges overlapped with that of the group studied are examined on the basis of intergroup contacts.     

A preliminary study of selective visual attention in female mountain gorillas (Gorilla gorilla beringei)

Visually attending to conspecifics can give group-living primates important ecological information, help them to anticipate the behavior of others and to regulate interactions with them, and provide other valuable social information. Variation in the importance and quality of social relationships should influence the way individuals selectively attend to fellow group members. Preliminary data on visual monitoring of conspecifics by wild female mountain gorillas (Gorilla gorilla beringei) show that selective attention mirrors variation in social relationships. Social bonds between males and females are central to gorilla society; correspondingly, females are more likely to stop feeding, and focus their attention on males who walk into view than on females, especially when males give dislays. Females are more likely to focus on other females with whom they have antagonistic relationships than those (mostly close relatives) with whom they have affiliative, cooperative ones. Further research on the context and consequences of visual monitoring could help to address questions about the regulation of social relationships and about social cognition in gorillas.     

The birth of a wild mountain gorilla (Gorilla gorilla beringei)

The live birth of a wild mountain gorilla is described. Details of the birth process are given along with the mother’s periparturitional behaviour and the responses of others to the birth. The mother, a multiparous female, gave no observable indication that birth was imminent, and delivered her infant quickly and easily. During parturition, a subadult male showed interest in the proceedings. Following delivery, several animals approached the mother, who then left the birth site. The mother cleaned her infant and by two hours postpartum had established ventro-ventral contact and, possibly, nursing. These data are related to relevant observations from the literature and unpublished data on other animals from this study.     

Observations on the teeth of the mountain gorilla (Gorilla gorilla beringei)

Measurements of a sample of mountain gorilla (Gorilla gorilla beringei) teeth are presented: when compared with other Gorilla series, the dimensions of the maxillary teeth fall in the upper end of the observed range for the genus. All of the upper teeth except the canine show a greater sex difference in the bucco-lingual diameter than in the mesio-distal dimension. This is also true for the other hominoids which have been studied, man, the chimpanzee, and the orang-utan, but to a lesser degree in man and the chimpanzee.     

Natural regeneration and ecological recovery in Bwindi Impenetrable National Park, Uganda

This study tests the justification for displacement and compensation of persons in a previously settled land for natural ecological recovery, and helps in the understanding of patch dynamics in a semi‐mountain tropical rain forest environment. The study area comprised parts of the Mbwa River Tract in Bwindi Impenetrable National Park in Uganda that had been settled and cultivated for at least 20 years prior to park reclassification. The extent, state and speed of regeneration of the cleared forest (CF) after resettlement were not known. There was therefore need for a baseline study as prerequisite for future ecological monitoring of forest recovery. Strip‐plots at 200 m intervals running across the tract were therefore established for this study. 1.17 km² of forest had been cleared for cultivation in the tract and regeneration in adjacent forest (MF) was better than in the CF, based on the abundance of seedlings. The CF was more diverse in species composition than the MF, and with predominantly pioneer tree species growing. The CF was ecologically important as a water catchment area and a habitat for several animal species, and there were indications that it was heading for ecological recovery.     

Dietary Variability of Mountain Gorillas in Bwindi Impenetrable National Park,Uganda

Data on intraspecific dietary variability has important implications for understanding flexibility in foraging behavior, habitat utilization, population dynamics, and social behavior and may also assist in conservation efforts. We compared food availability and diet of a group of mountain gorillas (Gorilla beringei beringei) at a high altitude site and 2 groups at a low altitude site in Bwindi Impenetrable National Park, Uganda, from September 2001 to August 2002. Plant species diversity was greater at the low altitude site than at the high altitude site. The two groups at the low elevation consumed more plant species (140 species vs. 62 species), and a greater number of fruit species per mo (7 vs. 3 species) and per yr (36 vs. 11 species) than the high altitude group did. Furthermore, each group shared <51% of important fibrous food items in their diet with the 2 other groups. There is no significant difference in the proportion of days fruit remains were found in the dung among groups. Finally, according to Ivlev's electivity index, all groups positively selected the majority of food items in their diets. We attribute a large proportion of dietary variation between locations to differences in fruit availability and plant species composition between sites. Differences between groups at the low altitude site may be due to variation in food profitability—more profitable foods available to choose in the same area—within their overlapping home range, or group traditions. A comparison of our results with the diets of gorillas of the Virunga Volcanoes in Rwanda and Kahuzi-Biega, DRC shows that eastern gorilla populations have highly variable dietary patterns with limited overlap in species consumed among groups and populations.     

The influence of male mating tactics on habitat use in mountain gorillas (Gorilla gorilla beringei)

Previous research has shown that both ecological and social factors influence mountain gorilla habitat use. New data on habitat use by a male gorilla and by a group confirm that male mating competition influences short- and long-term habitat use patterns, and show that its influence can supersede that of ecological factors on a long-term basis. When solitary, the male regularly approached and sometimes followed groups. His monthly home range size and equitability of home range use were directly proportional to the number of such interactions per month. His relationships with other groups became more conservative after he gained females, and, contrary to expectations based on metabolic needs, he used a much smaller area. The group considered here gradually expanded its home range and shifted its areas of intensive use throughout a three-year period. It then made a complete home range shift after three dramatic interactions, during which it was temporarily fragmented and two females emigrated. The group shared its home range with many other social units; overlap with most of these decreased after the shift. The degree of overlap and the lack of site fidelity by males and their groups support the argument that transfer is not ecologically costly to mountain gorilla females.     

Activity rhythm and the ranging of a solitary male mountain gorilla (Gorilla gorilla beringei)

To clarify the advantages of solitary life in gorilla males, a lone silverback mountain gorilla (Gorilla gorilla beringei) was studied for nine months in the natural habitat of the Virunga volcanoes. While the time budget for each activity and daily activity cycle were similar to those of groups, his daily journey distance and ranging patterns differed from those of groups. His movements were little influenced by the distribution and abundance of foods, which strongly influence the movements of groups. He notably increased his day journey distances when he encountered neighboring groups. He persistently followed the groups for days and went out of his usual range area. These encounters shifted his monthly range from his natal group's range to that of other groups. When the silverbacks of the encountered groups noticed his presence, they usually gave hoots and chest-beats and sometimes fought violently with him, while females and immatures did not show positive responses towards him. Lone males could have more chance to contact females and to lure them away from their groups than silverbacks within groups. The lone male stage, accompanied by frequent contacts with different groups, probably provides maturing males with useful knowledge of neighboring groups and areas.     

Movement patterns of a group of free-ranging mountain gorillas (Gorilla gorilla beringei) and their relation to food availability

Relationships between the movement patterns of free-ranging mountain gorillas (Gorilla gorilla beringei) and the abundance and distribution of foods in their home range were examined. During an 18-month field study, the ranging of one group of G. gorilla beringei was recorded on a 250 × 250 m grid system, from which measurements of frequency and duration of use, travel rate, and rate of revisitation of each quadrangle by the group were derived. Food items were sampled in selected quadrangles throughout the home range and various measures of food abundance, frequency and diversity were calculated. Analyses based on both spatial and temporal variation in food availability give supporting evidence for the prediction that mountain gorilla ranging patterns are influenced by the distribution and abundance of foods. Quality of food appears to be an important factor, as shown in analyses of yearly patterns and monthly changes in ranging. The gorillas studied spent more time in the higher quality areas of their home range, responded to a correlate of decreasing food abundance by increasing their rate of travel and area used, and revisited regions more frequently when the renewal rate of foods was clearly greater. Each of their foraging tactics can be explained as serving to increase the efficiency of harvesting foods.