Survey Results of Gorillas Frequenting the Mongambe Bais

Dense tropical vegetation has been a confounding factor in the collection of adequate behavioral observations of western lowland gorillas (Gorilla gorilla gorilla). However, in recent years, studies concentrating at forest clearings (open, grassland areas called bais or salines), such as Mbeli Bai in the Nouabalé-Ndoki National Park and the Maya North saline in the Odzala National Park within the Republic of Congo have provided excellent viewing conditions for studying western lowland gorillas' population dynamics and socio-behavioral ecology.
From October 1998 through February 1999, a pilot study was conducted within the Central African Republic's Dzanga sector of the Dzanga-Sangha Special Reserve at the Mongambe research site (2° 55' 04" N, 16° 23' 20" E). The reserve is under the collaboration management of the government, the World Wildlife Fund and LUSO consult for the German Technical Cooperation (GTZ). The Dzanga sector has one of the highest documented densities of western lowland gorillas at 1.6 weaned individuals/km² (Blom, 1999 and personal communication). Previously, Mongambe was a base for a primate eco-tourism program, concentrating on the habituation of gorillas via tracking. This project was relocated in 1997 to another site (Bai Hokou) within the same sector (Alma, et al., 1999; Blom, 1999; Cipolletta, 1999).
Based on the frequency and duration of gorilla observations recorded within the adjacent Nouabalé-Ndoki Park, this pilot study was conducted to determine whether gorillas at Mongambe similarly use bais and, if so, the feasibility of a long-term investigation. It was hoped that like similar studies, the continual proximity of researchers at platforms located next to the bais would acclimate the gorillas to human presence and hence, passively provide a means of habituation.
Using a global positioning system (GPS), Mongambe's 50 km² area was surveyed, and the bais' locations and dimensions were mapped. A total of five bais were located. One of these, a larger clearing connected by narrow corridors, was further divided into three areas to facilitate observations, resulting in a total of seven.
The bais range in size from the smallest at approximately 0.15 km long x 0.1 km wide to the largest of 0.7 km long x 0.4 km wide. For observational and recording purposes each bai was arbitrarily categorized in size as small, medium or large. Temporary platforms at the edge of four of the seven bais ensured good viewing to the major parts of the clearings. A total of 460.5 hours of observation time was logged. Both direct contacts (visual and/or auditory) and indirect evidence (prints, feeding traces, fecal matter, and nests) were noted at the bais and within close proximity (0.5 km). Evidence of gorillas, either as groups or solitary males, occurred at six out of the seven bais.
The sample set was too small for statistical analysis. All direct (visual and/or auditory) contacts were made either in the early morning or late afternoon and the number of elephants visiting the bais increased three-fold during the study period for the duration of the dry season. The frequency of visual contacts totaled 15 (11 of solitary males and 4 of groups) and the frequency of auditory contact for both groups and solitary males totaled 46. Determination of auditory contact as being either from one or more animal was not always possible. Indirect evidence (prints, feeding traces and nests) for both groups and solitary males totaled 53, 31 and 3, respectively (54 of solitary males and 33 of groups). The tendency to encounter or find evidence of solitary males, rather than groups, is also apparent when the data are broken down according to bai size. Combining visual contacts with indirect evidence, the frequencies were 31, 19 and 15 for solitary males vs. 23, 7 and 7 for groups at small, medium and large bais, respectively.
The results indicate that gorillas do visit bais in the Mongambe area; however, it appears that these visitations are less frequent than those recorded by observers at Mbeli or Maya North. Possible contributing factors to these differences, both within this study and between sites, may be population demographics, elephant density, variation of food plants, poaching, and proximity of human populations.
Due to the number of bais at Mongambe and the distance between them, a long-term behavioral investigation of the gorillas at the bais would necessitate either an increase in the number of researchers and/or the installation of surveillance-type cameras at every platform. These cameras would be used to record the presence of any animals, including gorillas, which visit the bais when researchers are not present.

Lyna M. Watson, Angelique Todd

References
Alma, A., Blom, A., Prins, H. (1999) The Mongambe Research Camp, Dzanga-Ndoki National Park, Central African Republic. Gorilla Conservation News 13:5-6.
Blom, A. (1999) Dzanga-Sangha Project Technical Report: Ecological Monitoring. World Wildlife Fund, Central African Republic.
Cipolletta, C. (1999) Habituation de gorilles pour un tourisme de vision a Dzanga-Sangha, en Centrafrique. Canopée 13:22-24.

Dr. Lyna M. Watson is Affiliated Scientist at the Zoo of New England, Boston, USA. Presently she is conducting a study on zoo gorillas. Moreover, she is employed as Director of Animal Welfare and Behavioral Management.
Angelique Todd is a Doctorate student at Manchester Metropolitan University. She also assists WWF personnel in the habituation process of two gorilla groups at Bai Hokou.

Western gorilla overview

Homepage