LONDON (Reuters Life!) - British researchers found they could relieve the stress of monkeys on show in a zoo by planting tropical shrubs in front of their enclosure.
Since the shrubs were installed at the Chester Zoo in northwest England, researchers said they have seen a reduction in displays of stress and a rise in behavior which indicated the seven mandrill monkeys were more relaxed.
The monkeys had been showing signs of anxiety and tension -- baring teeth and pacing -- in reaction to gawking visitors passing by their glass-fronted enclosure.
"Visitors can further aggravate this stress as some people interpret the mandrills' behavior as amusing and start mimicking them," said Jan de Ruiter, who led the research team of anthropologists called in from Durham University.
The study showed a 16 per cent rise in sociable behavior like playing and communal grooming after the shrubs' arrival.
The type of behavior monkeys would show in the wild, such as climbing and eating, also increased by 13 per cent.
"As soon as the shrubs were positioned, we noticed an immediate improvement in the welfare of the mandrills, who displayed significantly less anti-social behavior," de Ruiter said in a press statement from Durham.
The research team -- who won a 1,000 pound ($2,009) Wild Animal Welfare Award for their work -- claim the shrubs not only improved the welfare of the monkeys, but provided visitors with a more realistic impression of their natural environment.
Mandrills are the world's largest monkey species and are found in the tropical rainforests of western and central Africa, notes from the Durham statement said.
The monkeys, which can live up to 25 years in captivity, can be recognized by their olive fur and the colorful faces and rumps of males.
The World Conservation Union says mandrills face a high risk of extinction in the medium-term future and the university's statement said they were often hunted for food in the wild.
"It is important to remember that life in the wild is not stress-free either, with factors such as predation, competition for food, and disease or injury," Chester Zoo research officer Sonya Hill said.