The south-western region of the Central African Republic includes one of the most pristine tropical forests in the whole of Africa. Located in the Congo basin, it remains a paradisiacal habitat, harbouring an exceptional faunal diversity: forest elephants, forest buffaloes, sitatungas, bongos, several duiker species, two species of forest pigs, and 10 primate species besides gorillas and chimpanzees. This great biodiversity and the presence of so many species of large mammals are the treasures of this area. Large mammals are important flagship species that, when endangered and charismatic, have the potential to attract international attention for their conservation.

The gorilla is a perfect example, raising great international attention. Even though continuous efforts have been made towards its preservation, further action still needs to be taken to protect such a charismatic primate. Throughout their range, western gorillas (Gorilla gorilla) are endangered not only by habitat destruction and poaching, but also by threats unrelated to human activities. As a consequence of the tremendous decline of western gorilla populations in Gabon and Republic of Congo due to Ebola outbreaks, the IUCN reclassified western gorillas as "critically endangered". Despite the great international attention, very little information based on direct observation is available on western gorilla ecology, behaviour and natural history, creating a crucial necessity to fill this gap.
The south-western region of the Central African Republic is also characterized by the presence of natural forest clearings ("bai" in the local Pygmy language) of different sizes. These allow an easy observation of large mammals, including gorillas and elephants, since the animals are attracted by mineral rich soil, clay and aquatic plants. Acknowledging the high biodiversity and the high tourist potential of the area, a system of protected areas was officially created in 1990. Under the direction of the Dzanga-Sangha Project, today named Dzanga-Sangha Protected Areas, it consists of 1) the Dzanga-Ndoki National Park, integrally protected, and 2) the Dzanga-Sangha Dense Forest Special Reserve where local people can carry out legal forest activities. The project is a partnership between the World Wildlife Fund (WWF), the Central African Republic government, and, since 1994, the German Technical Cooperation (GTZ). The long-term goals of the project are: 1) to protect the forest ecosystem from changes in forest cover due to the increase in logging activities and illegal hunting, and 2) to promote sustainable development in the region through a rational use of natural resources. Until now, Dzanga-Sangha Protected Areas has greatly contributed to the protection of western gorillas and forest elephants, preserving their habitat and supporting ecological and behavioural studies.
Today the Dzanga-Ndoki National Park, together with the Lobéké National Park in Cameroon and the Nouabalé-Ndoki National Park in the Republic of Congo, is part of a larger system of protected areas called the Sangha Trinational Complex. The Trinational Complex is one of the best examples of organized conservation planning in the Congo Basin covering contiguous lowland tropical rainforest of critical biological significance, and supporting one of the most pristine blocks of protected forest in Central Africa.
One of the several forest clearings in the Dzanga sector of the Dzanga-Ndoki National Park is Bai Hokou, chosen as a camp site in the forest and the headquarters for research and tourist activities. At Bai Hokou, the Dzanga-Sangha Protected Areas created the "Primate Habituation Programme" under the direction of Chloe Cipolletta, now run by Angelique Todd. Its long-term objective is to develop eco-tourism based on viewing of gorillas and other primates. Gorilla tourism draws national and international attention to problems involved in protecting the ecosystem where gorillas live, and increases support for higher conservation efforts. Good examples are found in Rwanda and Uganda, where gorilla ecotourism has been contributing significantly to the conservation of mountain gorillas (Gorilla beringei beringei) and the livelihood of local people.
Developing gorilla ecotourism in Central Africa, however, has been more difficult since western gorillas have been particularly challenging to habituate to human presence, much more so than mountain gorillas. Difficulties are linked to the lowland forest habitat (limited visibility and unclear tracks left by western gorillas) and differences in gorilla sociality (wider group spread, and possibly higher rate of changes in group dynamics in western gorillas in comparison to mountain gorillas). In Bai Hokou, gorilla habituation was successful thanks to the unparalleled knowledge of the forest by the native Ba'Aka Pygmies, who retain their traditional lifestyle in this area.
However, when habituating animals, especially primates, risks associated with habituation must be taken into account. The success of Bai Hokou in habituating western gorillas is also due to rigorous application of rules aimed at minimizing risks of disease transmission from humans to gorillas. In addition, the long-term action of the Dzanga-Sangha Protected Areas guarantees constant protection of the habituated gorillas that become more vulnerable to poachers, having lost their fear of approaching humans.
With respect to other Central African conservation projects, where gorillas are observed from platforms in open clearings, the unique advantage of Bai Hokou is that researchers and tourists can follow the daily life of this elusive primate deep into the forest and observe it in close proximity. The recent success of habituation of western gorillas is starting to gradually fill the gap in our knowledge of western gorilla socioecology. Until recently, information based on direct observation of gorilla behavioural ecology was limited to few specific habitats, such as forest clearings, or to the well studied population of mountain gorillas. Mountain and lowland habitats, and accordingly the socio-ecology of western and mountain gorillas, differ dramatically.
Long-term research and monitoring of habituated groups of western gorillas are fundamental to increasing our understanding of their nutritional and habitat requirements, their life history and their social dynamics, all critical information for their conservation. In Bai Hokou 4 western gorilla groups are currently identified and/or followed daily. Two groups are in the process of habituation; a third group, called "Mayele", is currently semi-habituated and almost ready to receive tourists and researchers; while the fourth group, "Makumba", is one of the only two groups of western gorillas in the whole of Africa fully habituated to human presence. The group was first located in 2001 by Angelique Todd, and since early 2002 it has been followed daily, becoming fully habituated only in 2007-2008. Thanks to the skilled Ba'Aka trackers this group is now located every day at the night nest site and followed closely from dawn to dusk, right up till the gorillas stop to build new nests for the coming night.
Since the commencement of the habituation, the group's composition has changed several times, including transfers of 3 subadult individuals, one death of a 1-year-old infant (of natural causes) and the ensuing transfer of his mother. Today group Makumba consists of 1 silverback, 3 adult females, 1 blackback, 3 juveniles and 3 infants.
In 2000, together with collaborators, I started to investigate in Bai Hokou how habitat and seasonal changes in food availability influence western gorilla feeding ecology, examining in particular gorilla food choice in relation to the nutritional and energetic value of available food. With my colleagues at the Max Planck Institute in Leipzig, we found that even though gorillas become more frugivorous when fruit is more available in the habitat, their energy budget and energy requirements do not change throughout the year. During periods of fruit scarcity western gorillas can still rely on high quality young leaves and herbs. Investigating the behavioural responses of gorillas to seasonal changes in food availability helps us to understand the diverse adaptations of apes to different environments, and provides us with insights into their resilience in response to habitat alteration associated with deforestation and forest degradation.
Currently I am collaborating with Sabrina Krief at the National Museum of Natural History in Paris to continue my research on western gorillas in the Central African Republic to obtain a complete picture of western gorilla food choice. We will integrate our previous data on nutritional and energetic values of gorilla food with new data from direct observations of gorilla feeding behaviour, with gorilla health monitoring (including fecal, urine and genetic analysis of each individual of group Makumba), and with phytochemical analyses of plants consumed by gorillas. Our aim is to understand whether gorillas choose plants also in relation to their health condition and the medicinal properties of plants, or only in relation to the nutritional value of plants. Our goal is also to investigate the ontogeny of food choice, focusing on possible social influences on young gorillas during acquisition of diet and information on plants.
Finally, we aim to quantify the overlap between gorillas and the native forest population of Ba'Aka Pygmies in the use of forest products. Preliminary results show that gorillas consume many plants used by the Ba'Aka in traditional medicine. Since this research requires the active involvement of the local Pygmy communities, we hope to increase awareness and understanding of the value of forest biodiversity for both local human and gorilla populations. One of the often quoted benefits of preserving tropical forests and its biodiversity both for apes and humans is its role as a reservoir of important medicinal components. This long-term research is part of a larger comparative project on great apes, supervised by Sabrina Krief, which will enhance our understanding of the interaction between our closest relatives and their habitat, providing important insights for understanding human origins and coevolution of great apes, humans, and diseases.
The success of habituating western gorillas in Bai Hokou has greatly contributed to their protection, and has permitted gorilla ecotourism as well as field research which has increased our knowledge of the species. A better understanding of socioecology, nutritional, energetic and habitat requirements provides useful information to improve conservation plans for this elusive species and can also help to inform gorilla management in captivity and in sanctuaries.

Shelly Masi

This article was first published in an earlier version in the Gorilla Gazette 21, 2009

^{Our sincere thanks go to the Ministries of Education and Water and Forests of the Central African Republic government for permission to conduct this research in the park, to the Dzanga-Sangha Protected Areas and the Bai Hokou staff for logistic facilities and administrative support. I am particularly grateful to the "Primate Habituation Program" directors C. Cipolletta and A. Todd for their support and great contribution. Thanks go to S. Krief and M. Robbins for their collaboration and supervision of the research projects. Special thanks go to the Ba'Aka trackers, for their incredible courage, for sharing their forest knowledge and for their dedication to their work. I especially thank my research assistant, Kemanda Bienvenu Florentin, a student of the University of Bangui, Central African Republic, who was trained in research methods and hopefully will play a long-term role in the future of the Dzanga-Sangha Protected Area projects. Cleveland Metroparks Zoo has greatly contributed to his training by providing funding for his salary in 2008 and 2009. My research was also funded during my PhD by the University of Rome "La Sapienza" (Italy), the Max Planck Society (Germany), and partially by the Zoos and Aquariums Italian Union (UIZA) and the Italian Primatological Association (API). My current research is part of a two-year post-doc supported by the Centre National de la Recherche Scientifique (CNRS) and the National Museum of Natural History (MNHN) in Paris (France).}