The population density and nesting behaviour of gorillas (Gorilla gorilla gorilla) was studied in the Ngotto forest, Central African Republic. We carried out a nest count along 94 km of transects. Also, the herbaceous vegetation of the understory was quantified and we attempted to assess the decay rate of nest sites. A total of 145 gorilla nests in 27 nest sites was found. We found 82.1% of gorilla nests > 2 m above ground. There was a significant correlation between the height of nests and the diameter of trees with nests. The density was estimated at 0.34–0.40 weaned gorillas per km2 depending on the value of nest site decay rate used. The herbaceous vegetation was scarce in the study site (42 out of 50 quadrats had no herbaceous stems). Compared with the gorilla population of the nearby Dzanga-Sangha forest, the population density of gorillas at Ngotto was lower but the proportion of nests found above ground was much higher. These differences are discussed and we suggest that they were the result of the scarcity of herbaceous vegetation in the Ngotto forest.

The Critically Endangered western lowland gorilla Gorilla gorilla gorilla is found at high density in the swamp forests of Lac Télé Community Reserve, northern Republic of Congo. Preliminary surveys for apes on the Reserve periphery in the 1990s indicated that this area may also contain high densities of apes and we wished to verify this. Using distance sampling methodology we surveyed 1,029 km2 of the south-eastern Reserve periphery including Raphia swamp forests. We recorded 1,021 ape nests along 21 2-km transects. Results indicated that ape density estimated from nest group density, excluding old and very old Raphia nests (which may decay slowly), was very high: 6.81 weaned apes km-2 (95% confidence interval 3.93–11.84). Gorillas built most of the nests recorded: their density was estimated at 5.25 individuals km-2 (2.70–10.19). Most nests were constructed in Raphia swamp forest despite it covering only 25% of the study area. These are among the highest recorded densities of apes in Central Africa but, as nest decay rates in swamps are unstudied, we also estimated densities based on hypothetically slow nest decay rates and published data from other habitats. Gorilla densities may be linked to availability of monocotyledons as food and the natural protection from hunting offered by Raphia swamps. Gorilla density in swamp forest is spatially and temporally variable and surveys are required to estimate ape populations elsewhere in this habitat. Most Raphia swamps in Congo are unprotected, including the periphery of Lac Télé Community Reserve; protection and management are required to assure their continued availability for apes.

During 1998–2000 extremely low densities of gorillas Gorilla gorilla gorilla and chimpanzees Pan troglodytes troglodytes were found in the Minkebe Forest block in north-eastern Gabon. When compared with data collected before 1994, these data suggest a catastrophic decline in ape populations in the area. We believe that this decline was caused by a disease epidemic. The period of decline corresponds with the Ebola outbreaks of 1994 and 1996 that occurred in the human population in the same area. Deaths of gorillas and chimpanzees were associated with both Ebola outbreaks. Data from nearby sites indicate that the epidemic was limited to the Minkebe Forest. Occurrence of such epidemic die-offs should be taken into account in conservation strategies for the long-term survival of ape populations. At the time of writing, an Ebola epidemic among humans in the Zadié Department east of Minkebe Forest has resulted in 53 deaths. In the neighbouring Republic of Congo, authorities have reported 43 deaths and at least 12 other cases of Ebola. These epidemics are believed to be linked to the handling and eating of dead apes.

Animal well-being and enrichment continue to gain importance in the maintenance of primates living in captivity. Positive reinforcement training (PRT) and/or playing interaction have been shown to be effective in improving the well-being of several species of primates. This research study evaluated the effects of applying a combination of these two techniques (training/playing therapy) on a group of lowland gorillas (Gorilla gorilla gorilla). The effects of this combination on the behaviour of captive primates have been given very little attention to date. The behaviour of a group of seven females was recorded in two different phases at Barcelona Zoo: before (periods 1 and 2) and after (periods 3 and 4) a series of changes were made to the composition of this social group. In each period, two phases were distinguished: i) baseline condition, after the subjects became used to the researcher, focal recordings were made of the group's regular behaviour and, ii) experimental condition, the training and playing sessions (‘gorilla play’) with two specific subjects began one hour before the group went to the outdoor facility. The frequency and duration of the behaviour observed in each of the recording conditions were compared. The results showed positive changes in the gorillas’ behaviour: stereotypies, interactions with the public, aggression between subjects and inactivity were all reduced, while affiliative behaviour and individual and social play-related behaviour increased. Moreover, the benefits of this therapy were observed in trained individuals and the rest of the gorillas in the group, which would seem to indicate that training/playing can be used to create a more relaxed atmosphere, reducing social tension and improving the well-being of all the subjects involved.

The aim of this study was to make preliminary assessments of the effects of human activities on the gorillas and other wildlife in the Dzanga-Ndoki Park and broader Dzanga-Sangha Dense Forest Reserve (RDS), Central African Republic. During a month-long survey in 1997, observation and sign of humans and large mammals, including ape nest-sites, were recorded on 81.2 km of line transects in three sectors of the park and reserve. Human activities, including intensities of logging and hunting, appeared to decrease with distance from the population centres and were lower in the park than in the reserve sectors. Encounter rates with sign of duikers Cephalophus spp., monkeys Cercopithecus spp. and Cercocebus albigena, elephants Loxodonta africana, and gorillas Gorilla gorilla gorilla were generally lower in regions of high human activity in the reserve than in the park sectors. Nevertheless, gorilla nest-site densities did not vary significantly between sectors or with human activity levels. A high frequency of zero (bare ground) nests at RDS suggests that gorilla surveys that rely on line transect methods and use nest decomposition rates from other studies may sometimes underestimate gorilla densities. This study suggests that current levels of exploitation in managed hunting zones of national forest reserves may be negatively affecting targeted wildlife populations in these zones. Assessments should be a regular part of efforts to monitor the health of wildlife populations in managed protected zones. Participation by Central Africans in research will continue to benefit conservation and development efforts.

Syngamid strongylids of the genus Mammomonogamus undoubtedly belong among the least known nematodes with apparent zoonotic potential and the real diversity of the genus remains hard to evaluate without extensive molecular data. Eggs of Mammomonogamus sp. are frequently found in feces of African forest elephants (Loxodonta cyclotis) and western lowland gorillas (Gorilla gorilla gorilla) in Dzanga-Sangha Protected Areas. Using sedimentation-based coproscopic techniques, we found the eggs of Mammomonogamus in 19·7% elephant and 54·1% gorilla fecal samples with 8–55 and 1–24 eggs per gram of fecal sediment for elephants and gorillas, respectively. We used a combination of light microscopy, scanning electron microscopy and analysis of cytochrome c oxidase subunit I (cox1) and a partial sequence of 18S rDNA isolated from single eggs to test the hypothesis of possible Mammomonogamus conspecificity in gorillas and elephants. Whereas 18S rDNA sequences were identical in both gorillas and elephants, we distinguished seven different haplotypes within the cox1. Two haplotypes were found in both gorillas and elephants suggesting sharing of Mammomonogamus. Assignment of the parasite to M. loxodontis is proposed. Provided sequences represent the first genomic data on Mammomonogamus spp.

Non-human primates occasionally exhibit behaviours thought to occur only in captivity that are considered abnormal. In particular, hair-plucking behaviour occurs across many species of mammals and birds. This study was the first to assess the phenomenology, demography and aetiology of this behaviour in captive gorillas across the Association of Zoos and Aquariums (AZA) population. A survey was sent to 52 AZA institutions housing western lowland gorillas. Hair-plucking behaviour occurred in 15% of the surveyed population with 62% of institutions housing a hair plucker. Individuals were most likely to self-pluck using their fingers. Individuals that were exposed as youngsters to a hair-plucking group member were significantly more likely to develop the behaviour themselves. There was also a trend toward solitary individuals being more likely to perform this behaviour. Future research needs include identifying hormonal correlates to this behaviour, understanding its relationship to acute or chronic stressors, and examining what causes this behaviour to fluctuate in frequency once it has developed.

This survey of the status of the three gorilla races was made in 1974. Part One, below, covers the western lowland race, and Part Two, to be published in the next Oryx, will discuss eastern lowland and volcano gorillas.

While the use of salivary cortisol as an index of hypothalamic–pituitary–adrenal (HPA) axis activation has increased rapidly in human studies, few non-human primate studies have used saliva samples. Nearly 300 h of behavioural data and over 400 saliva samples were collected from three young adult, male western lowland gorillas to document the feasibility and effectiveness of using salivary cortisol as an index of HPA activation in gorillas. Cortisol concentrations were significantly higher in morning samples than in afternoon samples, and there was a significant decrease in morning cortisol concentrations across the study period. Additionally, acute increases, followed by a return to baseline concentrations of cortisol were observed. Salivary cortisol concentration was found to correlate across individuals, indicating potential psychological attunement to environmental and/or social variables in these animals. Although no clear relationship between behaviour and cortisol concentrations was established, these results indicate that salivary cortisol is an effective technique for documenting HPA activity over an extended period of time, as it allows for detection of diurnal variation as well as acute changes in salivary cortisol concentrations.