Newly Discovered Gorilla Population in the Ebo Forest,Littoral Province,Cameroon

We report on a new population of gorillas discovered in November 2002 in the Ebo Forest, Littoral Province, Cameroon. We observed A group of q7 gorillas directly for 83 min, and they were in auditory range for 155 min. Further evidence of gorilla presence included 8 nest groups totaling 38 nests, distinctive feeding signs accompanied by footprints, and a gorilla cranium collected from the nearby village of Iboti. This newly discovered gorilla population is geographically intermediate between the 2 extant populations of western gorillas: Gorilla gorilla gorilla, the most populous gorilla subspecies living in Gabon, Equatorial Guinea, Congo-Brazzaville, Central African Republic and Cameroon to the south of the Sanaga River, and G. g. diehli or the Cross River gorilla, a small population of ca. 250 individuals on the Cameroon-Nigeria border. It is not possible to assign the new gorilla population to either subspecies on the basis of measurements of the single male cranium. Genetic analyses of freshly shed hairs, collected from gorilla nests, may help to resolve the taxonomic status of the Ebo gorillas.     

Are gorillas right-handed or not?

Comparative data on laterality of function in primates are useful for elucidating its evolution, including its link to asymmetry of cerebral structure. Recently the gorilla (Gorilla gorilla, Pongidae) has been nominated as the other hominoid species closest toHomo sapiens in terms of handedness. This study aims to scrutinise the 22 accounts of gorillas' hand preferences. Numerous shortcomings exist in the published literature on the topic, so that a firm conclusion is not yet possible. It is not yet clear whether gorillas are right-preferent, left-preferent, or ambi-preferent, and additional data are needed.     

Insectivory by Gorilla gorilla gorilla in Southeast Cameroon

Our study extends quantitative analyses of insect-eating by gorillas (Gorilla gorilla gorilla) to Cameroon. During a 2-mo period (May–June 2001), we recorded and analyzed feeding traces on plants and insects and in gorilla feces. We found 180 feeding traces, 17% of which involved insectivory. Seventy-eight percent of the fecal samples (n = 36) contained insects. Ants were found in 61% of the samples, termites in 39%, while 56% of the samples contained remains of other insects. We added 14 new species to the known insect diet of western lowland gorillas. Overall, social insects are predominant. The choice of prey by the Ntonga gorillas gives new clues for the existence of cross-cultural differences among gorilla populations. A comparison of the overall frequency of insectivory with those at other sites in Central Africa indicate a possible effect of forest disturbance on the insectivorous behavior of gorillas. The study suggests the existence of temporal variation in ant- and termite-eating by gorillas.     

Digesta Passage,Digestibility and Behavior in Captive Gorillas Under Two Dietary Regimens

Gorilla adaptation has been debated in recent years given the wide variation among diets of gorillas in different habitats. Gorillas are the largest of living primates, have large colons and should be capable of processing tough foods. Preliminary captive studies have suggested that they may well have long average gut retention times relative to smaller hominoids, which should facilitate digestive efficiency in their wild counterparts. Indeed, wild gorillas consume large amounts of fibrous foods as staples or fall-back foods across their range, in response to habitat-related or seasonal changes in fruit availability. Fluctuations in diet might be matched by changes in digesta passage and digestibility, with possible selective retention of harder to digest items. We further studied digestive processes via chemical cobalt and chromium markers to track liquid and solids, as they passed through the guts of gorillas at the San Francisco Zoo (SFZ). In addition, we examined the effects of variation in captive diets on intake, digesta passage, digestion and behavior. The SFZ gorillas exhibited high digestibility coefficients, and gut passage was long relative to those of smaller-bodied hominoids. The results permit us to understand more fully the relationships of digestive processes to adaptation and dietary flexibility in the wild and to inform the development of dietary recommendations to improve the well-being of captive gorillas.     

Spontaneous use of sticks as tools by captive gorillas (Gorilla gorilla gorilla)

The present report describes the spontaneous use of sticks, as tools by young adult gorillas (Gorilla gorilla gorilla) in a social group at the San Diego Wild Animal Park, CA, USA. Three 8-year-old gorillas (one female and two males) threw sticks into the foliage of trees, which the gorillas could not climb due to electric wire, to knock down leaves and seeds. Two of the three gorillas selected sticks that were more suitable (i.e. longer or thicker sticks) for throwing. Moreover, they looked up at the target (i.e. the foliage of the tree) before throwing and grasped the stick at a position appropriate, for throwing (i. e. the end of the stick). They were more likely to throw sticks when particular adult group members were not nearby. These two gorillas also pulled branches of trees toward themselves by using sticks to capture them (branch-pulling), and one of these two beat a branch with a stick to knock down leaves and seeds (branch-beating). One of these two gorillas used much longer sticks for branch-pulling than for stick-throwing, indicating that he was capable of task-dependent selection of sticks. Analyzing the spontaneous use of sticks as tools by gorillas in captivity can lead to a better understanding of not only their cognitive ability but also of their social relationships which may otherwise be concealed.     

Monitoring the reproductive status of female gorillas (Gorilla gorilla gorilla) by measuring the steroid hormones in fecal samples

The reproductive status of female gorillas (Gorilla gorilla gorilla) was estimated by measuring the sex steroid hormones in fecal samples instead of in blood samples. Fecal samples from female gorillas were used to examine the reliability of this non-invasive assay system, which included the extraction method for estradiol-17β (E₂) and progesterone (P) from fecal samples. Fecal samples from three female gorillas were collected daily for about 55 days, and fecal E₂ and P were assayed to clarify the fluctuation patterns of these steroids in the feces. Fecal sampling from one female was repeated for another 50-day period (starting 75 days after the end of the first observation period) and assayed to confirm if the menstrual cycle of this subject was ovulatory. Although fecal E₂ concentration measurements were quantitative by using this assay system, fecal P concentration measurements were semi-quantitative. Relative amounts of fecal P in fecal samples were estimated by using the values of B/B₀ (bound/total binding in the radioimmunoassay system). Two of the four fluctuation patterns of fecal hormones observed throughout the menstrual cycle for the three female gorillas were typical for normal ovulatory cycles. In the subject observed for two periods, one pattern was typical and the other atypical. The results show that this non-invasive method is simple and practical for monitoring the reproductive status of great apes as well as Old World monkeys.     

A Faithful Record of Stressful Life Events Recorded in the Dental Developmental Record of a Juvenile Gorilla

The pattern and rate of dental development are critical components of the life history of primates. Much recent research has focused on dental development in chimpanzees and other hominoids, but comparatively little is known about dental development in Gorilla. To date, dental chronologies for Gorilla are based on a sample of 1 and information about variations in the time and timing of crown initiation and completion is lacking. We provide data on dental development in 1 captive, juvenile, female, western lowland Gorilla gorilla gorilla of known age, sex, life events, and date of death (carefully documented as part of zoo records) that experienced various physical insults during her first year of life. The perfect natural experiment allowed us to test the association of the timing of accentuated stress lines in teeth with significant physiological and psychological events during ontogeny of this juvenile gorilla. We analyzed histological sections from 14 permanent teeth (maxillary and mandibular I1-M2) and assessed crown initiation (CI) and crown formation times (CFT) using short- and long-period incremental lines in both enamel and dentine; they are advanced for all teeth compared to previously published chronology. The data suggest a relatively accelerated pace of dental development in gorillas compared to chimpanzees and fit an emerging pattern of an accelerated life history schedule in gorillas. Data on the timing of major accentuated lines in the developing dentition are tightly associated with exact dates of surgical procedures and follow-up hospital visits as recorded on zoo medical records. Our data highlight the importance of captive individuals with well-documented medical records for studying life history.

Influencing Western Gorilla Nest Construction at Mondika Research Center

We collected nesting data from 512 fresh nest sites, including 3725 individual nests, of western gorillas at the Mondika Research Site, Central African Republic and Republic of Congo from 1996 through mid-1999. The mean count of nests of weaned individuals is 7.4 per nest site. Nest types included bare earth with no construction (45% of total), partial to full ground construction (34%), and arboreal (21%). Females, blackbacks, and juveniles as a combined age-sex class built significantly more arboreal nests (21% of total) than silverbacks did (2%). Proximate rainfall (independent of temperature) is significantly correlated with nest construction, i.e., as rainfall increased, silverbacks built more ground nests, and non-silverbacks built more ground and arboreal nests. Maximum daily temperature (independent of rainfall) is significantly negatively correlated with nest construction, i.e., as temperature increased, gorillas slept more often on bare earth without constructing a nest. Accordingly, we conclude that although nest building in gorillas may have innate components shared with other great apes, it is a flexible behavioral pattern that in some western populations is often not exhibited. It appears that when gorillas in this population build nests, they do so in response to both wet and cool conditions, and independently of diet, ranging, or group size.     

The subspecies concept in primatology: The case of mountain gorillas

The criteria for the application of subspecific units in living primate populations have received little attention relative to other vertebrate taxa, even though they have important implications for conservation strategies for many nonhuman primate populations. One of the most critically endangered primates is the mountain gorilla,Gorilla gorilla beringei, of which 600 animals exist in east-central Africa. FollowingSarmiento et al. (1996), taxonomists have proposed splitting these populations into two subspecies as part of a revised taxonomy of the genusGorilla. In this paper I review the application of the subspecies concept in primatology, using the gorillas of Bwindi Impenetrable National Park and the Virungas as case studies. An examination of genetic, morphological, biogeographic, ecological, and behavioral evidence indicates that reclassifying Bwindi gorillas as taxonomically distinct from those in the Virungas is not well supported and needs further study. Because taxonomy provides the basis of conservation management policies, a cautious and conservative approach to the subspecies question is warranted in the case of endangered primate populations.     

Buccal dental microwear variability in extant African Hominoidea: taxonomy versus ecology

Buccal microwear patterns on teeth are good indicators of the abrasiveness of foodstuffs and have been used to trace the dietary habits of fossil species, including primates and hominids. However, few studies have addressed the variability of this microwear. The abrasiveness of dietary components depends not only on the hardness of the particles ingested, but also on the presence of dust and other exogenous elements introduced during food processing. These elements are responsible for the microwear typology observed on the enamel surfaces of primate teeth. Here we analyzed the variability of buccal microwear patterns in African Great Apes (Gorilla gorilla and Pan troglodytes), using tooth molds obtained from the original specimens held in several osteological collections. Our results suggest that ecological adaptations at subspecies or population level account for differences in microwear patterns, which are attributed to habitat and ecological conditions within populations rather than differences between species. The findings from studies on the variability of buccal dental microwear in extant species will contribute to a better understanding of extinct hominids’ diet and ecology.     

Mineral content as a basis for food selection by western lowland gorillas in a forest clearing

The forests in northwest Republic of Congo contain a number of herbaceous swamp clearings that provide foraging sites for lowland gorillas (G.g. gorilla). A 10-month study at the Maya Nord clearing (Parc National d'Odzala) showed that feeding activities occupied 72% of the time visiting gorillas spent on the clearing. They fed on four plant species: Enydra fluctuans (Asteraceae), Cyperus sp., Pycreus mundtii, and Rhynchospora corymbosa (Cyperaceae) among the 45 species recorded on the clearing. These clearing food species have higher mineral contents (especially Na and Ca) than the dominant Marantaceae species (Haumania liebrechtsiana) that constituted a staple food plant for gorillas in this forest. They also have higher potassium contents and contain less lignin than non-eaten clearing items/species. Finally, the most actively searched for clearing food (Enydra fluctuans) was characterized by the highest amount of Na and Ca. These results suggest that the mineral content (especially in Na, Ca, and/or K) could determine the feeding selectivity of gorillas at the clearing. They also tend to confirm that the amount of fiber plays a deterrent role in food selectivity, as has been found by many authors. The high density of gorillas in that region could result from the combination of the large areas of Marantaceae forests that provide abundant though monotonous food, and the number of clearings that provide sufficient mineral supplies. Clearings should thus be considered as key habitats for the conservation of gorillas.     

Beiträge zur Menschenaffenhaltung im Zoo Berlin nach 1945. 3. Mitteilung: Gorillas (Gorilla gorilla)

Since 1956 were Western Lowland Gorillas (Gorilla gorilla gorilla) kept in Berlin Zoo, counted in the period after 1945. The first offspring was born in 1964. Up to now 9 Gorillas were born in Berlin Zoo, of which 8 were raised, some of them artificial. The oldest Gorilla is “Fatou”, she is now in an age of 53.     

‘Separating the wheat from the chaff’: A novel food processing technique in captive gorillas (Gorilla g. gorilla)

Observation of a novel food processing technique is reported for captive zoo gorillas (Gorilla g. gorilla). It is similar in function to that of Japanese macaques' wheat placer mining behaviour and consists of puffing/blowing air with the mouth onto a mixture of oat grains and chaff in order to separate out the oat grains. Three females in two of four groups regularly use this behaviour. Other individuals in these groups or individuals of the two other groups in the same zoo do not use it. However, a very similar behaviour has been observed in three other individuals in a gorilla group of another zoo. The existence of this technique in spatially separated groups implies that multiple individuals have invented it for themselves. The possible role of social transmission is still to be investigated.     

Foods consumed by sympatric populations ofGorilla g. gorilla andPan t. troglodytes in Gabon: Some preliminary data

Data on foods consumed by gorillas and chimpanzees living in primary forest in Gabon were collected, mainly by examination of the contents of feces. Gorillas ate fruit very regularly (some fruit remains were present in 97.6% of 246 fecal samples examined), in addition to leaves, stems, pith, and bark. Some fruit remains were present in all chimpanzee fecal samples examined. Mean numbers of fruit species per fecal sample were 2.5 for gorillas and 2.1 for chimpanzees. Sixty percent of all identified foods recorded for gorillas were recorded for chimpanzees as well. Our results indicate that important differences in diet exist between western lowland gorillas and the eastern gorilla populations of Kahuzi-Biega and the Virunga Volcanoes. It is now clear that western gorillas cannot be accurately classed as folivores.     

The role of taste in food selection by African apes: implications for niche separation and overlap in tropical forests

Ripe fruit eating shapes the behavior of most of the apes. Gorillas (Gorilla gorilla) and chimpanzees (Pan troglodytes) are very different sizes and, consequently, have been traditionally viewed as ecologically distinct, but few studies have explored the behavioral and physiological foundations of their diets. Debate continues on the extent that large-bodied gorillas may be less selective and more opportunistic fruit eaters than chimpanzees. Taste responses have been predicted to relate to body size and digestive strategies. This study employs laboratory research on taste perception and discrimination among captive zoo-housed chimpanzees and relates it to previous work on gorillas to better characterize diets and niche separation among these apes. During the captive trials, differences were recorded in consumption patterns of water and varying concentrations of dilute aqueous fructose (sweet) and tannic acid solutions (astringent), compounds commonly found in wild foods. The chimpanzees exhibited similar preference thresholds for fructose (50 mM) to other primates studied. They exhibited slightly lower inhibition thresholds for tannic acid solutions than gorillas, but higher than smaller primates studied to date. These preliminary findings suggest that tannin tolerance may well be mediated by body size, though possible species differences in salivary proteins or other sensory differences remain to be explored. This research furthers our efforts to understand the roles of body size and physiological adaptations in shaping diet and niche separation of chimpanzees and gorillas.     

Medical Survey of the Local Human Population to Determine Possible Health Risks to the Mountain Gorillas of Bwindi Impenetrable Forest National Park,Uganda

There has been increasing contact between mountain gorillas (Gorilla gorilla beringei) and the human population surrounding Bwindi Impenetrable Forest National Park (BIFNP) in Uganda. Due to the close taxonomic relationship between humans and gorillas there is potential for disease transmission between them. Preventing the introduction or spread of transmissible diseases to the gorillas is essential to protect them. We interviewed 301 villagers living in close proximity to BIFNP with a medical questionnaire in July, 2000. We collected information on demographics, vaccination and health history, and human/gorilla interaction. Our objectives were to estimate the prevalence of several diseases in the human population and to evaluate the risk of anthropozoonotic transmission from humans to gorillas. We found a high prevalence of disease symptoms such as coughing (72.1%) and fever (56.1%) compatible with acute infectious diseases; over half of the respondents (59.1%) had a specific disease diagnosis within the 6 mo preceding the study. We compared villagers who had visual contact with gorillas in the 6 mo preceding the study (53.5%) to villagers who had no visual contact (46.5%). Men were 2.3 times more likely than women to have visual contact with gorillas. In general, the frequency of disease history and symptoms was similar for people with and without contact. The high prevalence of acute infectious diseases in the population surrounding BIFNP and the high rate of contact with gorillas creates the potential for anthropozoonotic disease transmission.