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.

Visitors to zoos can be a potential source of stress to captive-housed primates, resulting in increased abnormal behaviour and intra-group aggression. Finding a way to screen primates from human visitors may be one method of decreasing stress and enhancing animal welfare. For this study, the behaviour of six zoo-housed gorillas was studied for one month during standard housing conditions (control condition) and for a further month following the installation of a camouflage net barrier to the viewing area of the exhibit (barrier condition). Visitors’ (n = 200) perceptions of the animals and the exhibit were also recorded during each condition. The net barrier had a significant effect on some components of the gorillas’ behaviour. The gorillas exhibited significantly lower levels of conspecific-directed aggression and stereotypic behaviours during the barrier than the control condition. The net barrier also had a slight effect on visitors’ perceptions both of the animals and of their exhibit. The gorillas were considered to look more exciting and less aggressive during the barrier than the control condition. The exhibit was also considered to be more appropriate for visitors following the introduction of the camouflage netting. Overall, the addition of a screen such as camouflage netting could be considered a positive change, resulting in a reduction in those behaviours typically induced by large groups of visitors and an improvement in public perceptions of the animals and their environment.

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.

We investigated intestinal trichomonads in western lowland gorillas, central chimpanzees and humans cohabiting the forest ecosystem of Dzanga-Sangha Protected Area in Central African Republic, using the internal transcribed spacer (ITS) region and SSU rRNA gene sequences. Trichomonads belonging to the genus Tetratrichomonas were detected in 23% of the faecal samples and in all host species. Different hosts were infected with different genotypes of Tetratrichomonas. In chimpanzees, we detected tetratrichomonads from ‘novel lineage 2’, which was previously reported mostly in captive and wild chimpanzees. In gorillas, we found two different genotypes of Tetratrichomonas. The ITS region sequences of the more frequent genotype were identical to the sequence found in a faecal sample of a wild western lowland gorilla from Cameroon. Sequences of the second genotype from gorillas were almost identical to sequences previously obtained from an anorexic French woman. We provide the first report of the presence of intestinal tetratrichomonads in asymptomatic, apparently healthy humans. Human tetratrichomonads belonged to the lineage 7, which was previously reported in domestic and wild pigs and a domestic horse. Our findings suggest that the ecology and spatial overlap among hominids in the tropical forest ecosystem has not resulted in exchange of intestinal trichomonads among these hosts.

The frails of Cola lizae, an endemic tree with a limited geographical distribution, have been a major food source for lowland gorillas in the Lopé Reserve during part of each year over a six-year period. Faecal analysis indicated that 11,000-18,000 Cola seeds km-2 were deposited by gorillas during the 4-month season in 1989. Gorillas are the only important dispersers of this species: other primates consume the succulent mesocarp, but do not swallow the large seed; elephants do not eat Cola fruits. Observations of Cola seeds in gorilla faeces showed a very high germination rate and, despite initial high mortality, 18% of seedlings still survived six months after deposition. Survival of seedlings was significantly better in faeces left at nest-sites than in other areas of the forest: 40% of seedlings were viable at nest-sites six months after deposition. This suggests that the open areas of forest, preferred by gorillas as nest-sites, are advantageous to the propagation of this species.

Recent studies have shown that western lowland gorillas (Gorilla gorilla gorilla Savage & Wyman) are highly frugivorous and expel in their dung viable seeds of many fruit species they consume. As part of a wider study of their role as seed dispersers in tropical rain forest, the importance of gorillas as consumers of three species of tropical tree was investigated. The species studied were Ganophyllum giganteum (Sapindaceae), Cola lizae (Sterculiaceae) and Uapaca guineensis (Euphorbiaceae). Gorillas swallowed large quantites of seeds of these species whenever they were available, and removed a considerable proportion of the crop from trees they visited. The differences in abundance and distribution of these trees, and their varied dispersal strategies influenced the quantity of seeds that was removed by gorillas. Uapaca can be seen as having a generalist fruiting strategy, with a wide range of consumers, whereas the other species are more specialist, gorillas being the principal dispersers. Compared to other consumers, this study showed that gorillas provided potentially high quality dispersal because: (i) they were reliable visitors to trees of these species; (ii) they swallowed and dispersed large numbers of seeds; (iii) they treated seeds benignly and often deposited them in sites favourable for establishment.

Evidence is presented for the importance of western lowland gorillas as seed dispersers in the Lopé Reserve, Gabon. The survival and growth of seedlings of three tree species, growing from dung deposited at gorilla nest sites, were monitored for up to 2 y after deposition. A comparison was made between this and seeds (i) deposited in dung on gorilla feeding trails, (ii) dropped (spat out) under conspecific canopies, and (iii) scatter-dispersed (spat out) by other consumers away from conspecific trees but under intact forest canopy. The highest survival and the best performance of seedlings was always at a gorilla nest site, although not every site was favourable for survival or growth. Seedling performance was related to the surrounding vegetation conditions: better performance was observed in seedling clumps with less vegetation cover. Gorillas at Lopé apparently provide high quality seed dispersal for these species, not just because they consume large quantities of seeds, but because the pattern of seed deposition, especially in nest sites, can result in the enhanced survival and growth of seedlings.