Too close for comfort? Gorillas stressed by tourists

May 2010: Experts are recommending new guidelines for the observation of gorillas for both tourists and research teams after a study found that human presence could disturb the animals.

GOING HUNGRY: If humans get too close gorillas sacrifice time feeding to monitor their presence

A minimum observation distance of ten metres is now being suggested.

Ecotourism provides vital income for remote African communities, and as well as boosting local economies it has also convinced governments to invest in conservation and provided a deterrent for would-be poachers. Stressed gorillas spend less time feeding when humans are too close for comfort

A common cold can threaten a whole family
However, ecotourism is not without its risks. Gorillas are known to be vulnerable to human diseases - but with less hardened immune systems something as seemingly trivial as a common cold could prove fatal, and threaten an entire family of gorillas.

The current seven-metre observation guideline was originally set up to help guard against this. However researchers at the University of Stirling who studied a group of gorillas at Bai Hokou in the the Central African Republic documented the gorillas behaviour when subjected to human presence.

The study, which was led by PhD student Michelle Klailova, forms part of a long-term programme to monitor human impact on western lowland gorillas, with the aim of providing conservationist and wildlife experts to find ways to minimise the level of disturbance.

Michelle and her team followed one silverback male named Makumba for a year and recorded his vocalisations, daily activities and interactions with his 12 family members. She then compared these records with the size and type of the human group - which includes local trackers, scientists and often tourists - and its distance from the gorillas.

Even though the team respected the seven-metre limit, and kept their numbers low, Klailova found that their presence did affect the gorillas' behaviour. As the numbers increased, the gorillas spent less time feeding and instead engaged in unfocused, mixed behaviours.

Soft warning barks
‘Distance had the largest effect,' says Klailova. Makumba was more likely to stop feeding and start monitoring human behaviour as observers moved closer to him. As humans move closer, he sacrifices part of his feeding time to monitor us. This cannot be good.'

Aggressive behaviour towards humans also increased as their distance from the gorillas reduced. The gorillas begin to make soft barking noises - warning signals which, if ignored, can escalate into more aggressive actions such as charges. This behaviour increased most markedly when humans strayed closer than ten metres.

Seven metre distance too small - should be 10 metres minimum
The seven-metre minimum distance is based on disease transmission risk. Now Klailova and her team recommend in their American Journal of Primatology paper, ‘an increase of the minimum observation distance to ten metres, to incorporate the psychological stressors of close human contact'.

However, ideally, recommends the study, the distance would be even further. At 18 metres the gorillas stop reacting to human presence - although Klailova accepts that ‘this is not a realistic goal in dense forests, for researchers and especially for tourists, who have spent valuable time and effort to see the gorillas'.

While it is clear that humans have an effect on the gorillas, Klailova believes that it's important to put this into perspective. ‘Human factors explain only ten per cent of the overall variance in the results, which means that there are many other important, but yet undetermined, non-human factors that are affecting the gorillas behaviour,' she says.