Pathology and diseases of great apes at the National Zoological Park

Knowledge of the diseases of great apes in captivity is essential for captive management of self-sustaining populations. This survey of medical and pathology records of orangutans, gorillas, and one chimpanzee at the National Zoological Park was conducted to provide a data base for improving health care of captive apes. Strongyloidiasis, balantidiasis, and entamoebiasis were recurrent problems in adult and juvenile apes of all species. Cardiac fibrosis also was prevalent in middle-aged apes and was a major cause of mortality. Bacterial infections were prevalent in perinatal orangutans and resulted in the death of two. For gorillas, rheumatoid arthritis associated with mycoplasma infections, and infertility were major problems. Because the pathogenesis of many of these lesions is unknown, survival of great ape populations in captivity may depend on future research on these problems.     

A unique genomic sequence in the Wolf-Hirschhorn syndrome [WHS] region of humans is conserved in the great apes

The Wolf-Hirschhorn syndrome (WHS) is caused by a partial deletion in the short arm of chromosome 4 band 16.3 (4p16.3). A unique-sequence human DNA probe (39 kb) localized within this region has been used to search for sequence homology in the apes' equivalent chromosome 3 by FISH-technique. The WHS loci are conserved in higher primates at the expected position. Nevertheless, a control probe, which detects alphoid sequences of the pericentromeric region of humans, is diverged in chimpanzee, gorilla, and orangutan. The conservation of WHS loci and divergence of DNA alphoid sequences have further added to the controversy concerning human descent.     

Seasonal change in the composition of the diet of eastern lowland gorillas

Details are presented of the composition of the diet of eastern lowland gorillas, derived mainly from a study of their fresh trails and fecal analysis, during the course of an entire year in the tropical lowland forests of the Itebero region, Zaire. Gorillas ate 194 plant foods from 121 species and 45 families. They consumed 48 species of fruits; and 89% of fecal samples contained fruit seeds, but fruits were a relatively small part (25%) of the total number of food items. The composition of their diet changed seasonally. When consumption of fruit decreased in the long rainy and the long dry seasons, the gorillas ate, in addition to Zingiberaceae and Marantaceae, many kinds of leaf and bark, which may be an important buffer against the shortage of fruits. Gorillas also fed regularly on ants (Ponerinae), and the frequency of consumption showed small seasonal variations. From a comparison of diet composition, eastern lowland gorillas appeared to be intermediate between the other two subspecies. The choice of food showed differences in preference of fruits and insects between subspecies and may reflect high similarities within subspecies in lowland and montane forests.     

The effect of visitors on the behavior of zoo-housed western lowland gorillas (Gorilla gorilla gorilla)

Primates, especially apes, are popular with the public, often attracting large crowds. These crowds could cause behavioral change in captive primates, whether positive, neutral, or negative. We examined the impact of visitors on the behavior of six western lowland gorillas (Gorilla gorilla gorilla), observing the troop over 6 weeks during high season (4.5 hr/day, 35 days, May–July 2016). We used focal scan sampling to determine activity budget and enclosure usage, and focal continuous sampling to identify bouts of anxiety-related behavior (visitor-directed vigilance, self-scratching, and aggression). Both daily zoo-entry numbers (V_GATE) and instantaneous crowds at the exhibit (V_DENSITY) were measured. Overall, V_GATE had little effect across behaviors. However, consistent with the more acute time frame of measurement, V_DENSITY was a better predictor of behavior; at high crowd volumes, we observed significant group-level changes in activity budget (increased inactivity, increased locomotion, and decreased environment-related behaviors), increase in some anxiety-related behaviors, and decreased enclosure usage. Although contributing similar effects, it could not be determined if crowd numbers, composition, or noise most affected the troop, nor any chronic effects of exposure to large crowds. Nevertheless, our findings suggest that measures to minimize the impacts of large crowds at the exhibit would be beneficial. Furthermore, we highlight potential discrepancies between common methods for measuring visitor numbers: V_GATE is less sensitive to detecting visitor effects on behavioral indices than V_DENSITY. Future studies should appropriately match the biological time frame of welfare indicators and visitor measures used to ensure the reliability of findings.     

Using behavior to determine immature life‐stages in captive western gorillas

Ontogenic development is divided into infant, juvenile, adolescent and adult life‐stages. Although the developmental trajectory of an individual is a flexible entity, which differs within species, environment and sex, life‐stage classifications are generally structured, age‐based systems. This invariably leads to rigidity within a dynamic system and consequently hampers our understanding of primate life history strategies. We propose that life‐stage classifications should be quantitative, flexible entities, which use a reliable measurement of development. Here, we provide a methodological example where placement into a life‐stage is based upon behavioral variance between other similar‐aged individuals. Behavioral data were collected from 12 male (3–11 years old) and 9 female (3–8 years old) captive immature western gorillas (Gorilla gorilla gorilla) housed in five family groups, using continuous focal sampling; 900 hr of data were collected over 131 days. Data were applied to four published life‐stage classifications for mountain gorillas (Gorilla beringei beringei), which showed variable ability to determine life‐stage in western gorillas. A new life‐stage classification (Hutchinson & Fletcher) was proposed specifically for western gorillas, whereby multiple co‐varying behavior provided a robust measure of linear development across immaturity. Each life‐stage was found to be a distinct ontogenic phase and the classification discriminated life‐stage with a high level of accuracy. Using the Hutchinson & Fletcher classification we provide evidence for disparity in developmental trajectories between the sexes from the juvenile period onwards. To expand the understanding of primate life histories, we propose that flexible classifications should be used to enable comparison of allometric life history traits within and between species, from birth onwards. Am. J. Primatol. 72:492–501, 2010. © 2010 Wiley‐Liss, Inc.     

Fracture toughness of mountain gorilla (Gorilla gorilla beringei) food plants

Mountain gorillas, the largest extant primates, subsist almost entirely on plant matter. Moreover, their diet includes a substantial amount of structural material, such as bark and stems, which other primates tend to avoid. Accordingly, the robust masticatory apparatus of gorillas may be adaptive to this presumably tough diet; however, quantitative information on this subject is lacking. In this study the fracture toughness of mountain gorilla foods was examined for the first time. Samples of 44 food plants from Bwindi-Impenetrable National Park (BINP) and Mgahinga Gorilla National Park (MGNP) were tested. These parks are inhabited by two gorilla populations that regarded by some as being distinct at the subspecific taxonomic level. Although food toughness did not differ between the two populations, both diets contained tough items. Tree barks were the toughest food items (varying from 0.23 to 8.2 kJ/m2), followed by shrub barks, pith, and stems. The toughness of leaves and fruit was negligible compared to that of bark. The toughness of bamboo was low in comparison to the toughest food items. Accordingly, the prominent toughness of bark, pith, and stems may be key factors in the evolution of orofacial robusticity in mountain gorillas.     

Social structure and life-history patterns in western gorillas (Gorilla gorilla gorilla)

Life-history traits and ecological conditions have an important influence on primate social systems. Most of what we know about the life-history patterns and social structure of gorillas comes from studies of eastern gorillas (Gorilla beringei sp.), which live under dramatically different ecological conditions compared to western gorillas (Gorilla gorilla sp.). In this paper we present new data on western gorilla social structure and life histories from four study sites, and make comparisons with eastern gorilla populations. Data were obtained from two study sites with gorilla groups undergoing the habituation process (Lossi, Democratic Republic of Congo and Bai Hokou, Central African Republic) and two "bai" studies (Maya Nord and Mbeli Bai, Republic of Congo). The size and structure of these groups were similar to those seen in eastern gorillas. However, differences in the occurrence of various group transitions (group formations, changes between one-male and multimale composition, and group disintegrations) exist, and western gorillas notably exhibit much higher rates of male emigration and correspondingly fewer multimale groups compared to mountain gorillas. Certain phenomena have been observed only rarely, including predation by leopards. The preliminary data show no significant differences in birth rates between western gorillas and mountain gorillas. The ecological variability across gorilla habitats likely explains the flexibility in the social system of gorillas, but we need more information on the social relationships and ecology of western gorillas to elucidate the causes for the similarities and differences between western and eastern gorillas on the levels of individuals, social groups, and population dynamics.     

Home-range use and intergroup encounters in western gorillas (Gorilla g. gorilla) at Lossi forest, North Congo

I present data on home-range use and types of intergroup encounters for one group (Apollo) of western gorillas (Gorilla gorilla gorilla) from a new study site in the Republic of Congo. The total home-range size of the focal group, which I calculated by superimposing a 100 m x 100 m grid over the mapped daily path traveled, was 11 km2. The majority (73%) of the group's home range was used exclusively, although at the periphery it overlapped with the ranges of three other groups. Most encounters (86%) with other groups (n = 14) took place in the periphery of the home range, and appeared to involve access to fruit trees. The focal group silverback's encounters with solitary silverbacks occurred throughout the focal group's home range, did not involve access to fruit, and typically resulted in aggressive or avoidance behavior. The focal group silverback's response to other group males was more varied: it included tolerance (64%), avoidance (14%), and aggression (21%), and was dependent upon the identity of the extragroup male. The focal group exhibited an unusual form of tolerant behavior toward some other groups by occasionally forming "nesting supergroups" (two groups nested together overnight at distances of 30-50 m). The western gorillas at Lossi were somewhat fluid in their grouping. Subgrouping and supergrouping occurred, although more infrequently than reported previously, and with a new twist: subgrouping did not necessarily require a silverback's presence. I stress the need for intraspecific comparisons and more complete data sets on western gorilla social organization.