By Victoria Gill
Science reporter, BBC Nature
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The most innocuous interactions with tourists can upset endangered Barbary macaques, say scientists.
A study revealed that macaques at a site regularly visited by tourists showed signs of anxiety when people got too close, fed them or tried to attract their attention for a photograph.
The scientists monitored the monkeys' behaviour and also tested the animals' droppings for stress hormones.
The results are published in the journal Biological Conservation.
"There's been a lot of interest, recently, in tourism and how it affects wild animal populations," explained Dr Stuart Semple, a scientist who specialises in the study of primates at the University of Roehampton in London, UK.
Like humans, macaques fidget and scratch when nervous
"But while there are studies that show tourism does affect animal behaviour, we've tried to look at it much more directly, and to actually measure their levels of anxiety."
Laetitia Marechal, also from Roehampton, led the study.
She and her colleagues studied 50 days of tourist-monkey interactions at Ifrane National Park in the Middle Atlas Mountains of Morocco.
A population of macaques here has become habituated to the regular visits of tourists for at least five years.
"The more tourists there were, the more anxious the macaques would become," said Dr Semple.
"Just like humans, macaques scratch themselves when they're nervous or anxious, so we use this [scratching behaviour] as a measure of their level of anxiety."
The researchers divided the interactions into three categories: feeding; neutral, which included taking photographs of the monkeys; and aggression, including the less common incidences of tourists throwing things at the macaques or physically striking them.
"All three types of interactions seemed to make the monkeys anxious," said Dr Semple.
Being too close can make macaques feel anxious
"We were unsuprised by the aggression and the feeding, but we were surprised that tourists doing the usual tourist thing upset the animals."
The next stage of the study looked for chemical evidence of stress in the macaques' droppings.
"We collected fecal samples and measured the levels of stress hormones in them," explained Dr Semple. "When you become anxious, your body doesn't necessarily become physically stressed, so this was an important measurement."
The results suggested that only the aggressive interactions with tourists cause the monkeys to become physically stressed. But Dr Semple says that, for the well-being of these intelligent animals, tourists should avoid making them nervous or anxious.
"It would be very straightforward to develop some general guidelines," he told BBC Nature. "For example, not allowing tourists to get too close to the animals and asking people to keep noise levels down a little bit. Just a few simple things.
"This could actually make the experience [of viewing wildlife] much better for people as they would be able to enjoy the animals as they behaved in a much more natural way."