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Gorilla Trekking

The Rules and Reality of Mountain Gorilla Tracking

The Rules and Reality of Mountain Gorilla Tracking

Gorilla Trekking

The tracking of mountain gorillas (Gorilla beringei beringei) generates enough revenue to cover park management costs and contribute to the national budget of the Uganda Wildlife Authority (Archabald & Naughton-Treves 2001). As a result, tourism is generally considered a crucial component of gorilla conservation strategy (Weber 1993; McNeilage 1996). There are however several concerns about the effectiveness of tourism as a conservation tool in this context (Butynski & Kalina 1998), foremost amongst which is the risk of diseases being transmitted to gorillas. An event of this kind could have devastating consequences for this critically endangered species (Homsy 1999; Daszak et al. 2000; IUCN 2006).

While gorillas are perhaps most at risk from catching diseases from park staff, researchers, and local people living in their habitat (Wallis & Lee 1999; Guerrera et al. 2003), tourists also pose a significant threat because (1) there is a high level of exposure to tourists as habituated gorilla groups experience close contacts with a group of tourists every day, (2) they may bring with them novel infections to which the gorillas have no immune response, and (3) it has been found that some tourists visiting chimpanzees in Uganda show symptoms of risk diseases such as diarrhea, coughing and respiratory distress (Adams et al. 2001). Gorillas can be vulnerable to human gut and skin parasites (Sleeman et al. 2000; Kalema-Zikusoka et al. 2002), but airborne diseases are believed to represent the greatest threat posed by tourists (Homsy 1999).

The degree of health threat posed by tourists depends on a number of factors: whether any tourist is infected with a risk disease, and, if so, the infectiousness and mode of transmission of that disease (Woodford et al. 2002); how close tourists get to the gorillas, as the risk of infection with diseases transmitted by air increases with increasing proximity (Homsy 1999); the number of tourists in the group and the duration of their visit, as the risk of transmission is linked to exposure to infectious individuals; and the characteristics of the gorillas that come into close contact with humans, as juvenile gorillas are considered more vulnerable to human diseases than adults (Graczyk et al. 2001) and are more curious and likely to approach humans (A. McNeilage, pers. comm.).
Taking these risk factors into account, tourists are expected to abide by a number of rules during their visits to gorillas (for full details of all tracking rules see IGCP 2005). Successfully enforcing gorilla tracking rules is difficult because of gorilla and tourist behaviour, and because guides may allow rules to be broken in pursuit of tips or as a result of accepting bribes (McNeilage 1996; Butynski & Kalina 1998). Infringements of gorilla tracking rules have been widely reported (Aveling 1991; McNeilage 1996), but to date there has been no study that sets out to quantify them systematically. This study from Bwindi meets this need by measuring how close tourists get to gorillas, how these close contacts are initiated, the age class of gorillas with which close contacts occur, and the duration of contacts.

Data were collected between February and December 2004. Tourists attended a Uganda Wildlife Authority briefing session in the morning before tracking, at which they were asked if they would be willing to be interviewed. Those accepting were visited for interview in the afternoon following their return from the forest.

In each interview the purpose of the study was explained and the participant taken through a structured questionnaire that provided data regarding their visit to the gorillas. These were how close they got to the gorillas at the point of closest contact, how long this contact lasted, the age category (juvenile or adult) of the gorilla involved if known, the contact initiator (tourist or gorilla), and the typical distance from themselves to gorillas during the visit, defined as the closest distance tourists maintained to gorillas for at least 15 cumulative minutes during the hour (to give a measure of general encounter proximity ignoring passing close encounters of short duration). Distances were estimated using a tape measure, with respondents asked to hold one end of the measure while the interviewer backed away from them until the respondent felt the appropriate distance had been reached. Duration was estimated by tourists in seconds.


A total of 361 tourists were interviewed, representing 133 independent tourist tracking groups. While no physical touching events were reported, the mean distance between tourists and gorillas at the time of their closest contact was 2.76 m. This is significantly closer than the 7 m permitted under the current rule. The mean closest distance between tourists and gorillas maintained for at least 15 minutes during the tracking hour was 4.85 m, which again is significantly closer than the minimum allowable.

Contacts initiated by gorillas were closer than those initiated by tourists, and contacts with juvenile gorillas were closer than contacts with adults. Contacts with adults lasted longer than with juveniles, and contacts initiated by gorillas were shorter than those initiated by tourists.

There was no significant variation in closest contact proximity across guides. There was no significant correlation between tips given and closest contact proximity.


A previous study of primate tourism in Uganda demonstrated that humans visiting great apes are potential sources of infection (Adams et al. 2001), but did not investigate how close tourists get to these animals, a variable linked to the risk of a disease being transmitted (Woodford et al. 2002). The results of this study address this issue, and show that, in the case of mountain gorillas at Bwindi Impenetrable National Park, tourists get extremely close. The minimum distance rule of 7 m was broken on a daily basis, and contacts with juveniles were closer than with adults. The mean closest distance maintained for at least 15 minutes was significantly less than 7 m, indicating that encounters were not fleeting. These results demonstrate serious problems with the present rules, and that the risk of disease transmission might be greater than previously believed.

There are several factors that help to explain why tourists get so close to gorillas. Firstly, it has been suggested that excessively close encounters occur because gorillas are over-habituated and actually approach tourists, particularly in the case of inquisitive juvenile animals (Graczyk et al. 2001; Mudakikwa et al. 2001). This hypothesis is supported by the results of this study, because contacts initiated by gorillas were closer than those initiated by tourists, and contacts with juvenile individuals were closer than those with adults. Secondly, Bwindi Impenetrable Forest is dense, often making it impossible to get a clear view of the gorillas from 7 m away. This places guides under pressure to allow tourists to get closer so that they can see the gorillas clearly. The dense foliage and steep topography also make it difficult to retreat should a gorilla approach the group, and this limits guides’ ability to move their visitors back. This problem is likely to be exacerbated by the recent increase in the number of tourists allowed per group from 6 to 8. Thirdly, the gorillas within each group are often dispersed over a wide area, and tourists can find themselves surrounded by them, making it impossible to move away.

These constraints on guides’ ability to prevent tourists getting too close to gorillas suggest that in some situations it is impossible to stop excessively close encounters from occurring but cannot fully explain the results of this study. Although the closest encounters were initiated by gorillas, those initiated by tourists were still far closer than the allowable distance and lasted long enough to suggest that these were not accidental fleeting encounters. One tourist reported being less than 1 m from a gorilla for 10 minutes, an encounter both avoidable and unacceptable.
In defence of the guides, no evidence was found for performance differences between them or for a link between contact proximity and their tips. These findings are contrary to the expectations of some previous authors (McNeilage 1996; Butynski & Kalina 1998).

The results of this study demonstrate that at present the rules governing how closely tourists can approach gorillas at Bwindi Impenetrable National Park are failing, with the 7 m rule clearly not enforced. Even this distance may be dangerous as it is based on research into sneezing and is not a scientifically determined safe distance for gorilla viewing (Baker 1995; Homsy 1999). Changing this rule seems unlikely to help, as reducing or removing the minimum distance would suggest tourists could go closer, and increasing it would make it even less enforceable. Training of guides should be improved, but it seems inevitable that close encounters will go on occurring for as long as tourists are allowed to visit wild mountain gorillas. It may therefore be wise to consider adopting other measures for the reduction of disease transmission risk, such as surgical masks for tourists during their time with the gorillas (Adams et al. 2001) or medical screening and explicit vaccination requirements to reduce the chance of infectious tourists tracking gorillas (Homsy 1999). These possibilities now require urgent consideration because, if action is not taken, there is a risk that the tourists who believe they are supporting gorilla conservation will unwittingly contribute to their further decline.

Chris Sandbrook and Stuart Semple

This study was originally published in Oryx 40 (4), 428-433 (2006)

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