Unlike us, monkeys don't have earplugs for tuning out the din of city life, so instead they relocate to the quietest parts of their habitat — often at the expense of a full belly, a new study finds.
"Brazil is an extremely noisy country," study researcher Robert Young, of Pontifícia Universidade Católica de Minas Gerais. "Like a human, they [the monkeys] can move homes; they've chosen to move to a quiet part of the neighborhood because the noise bothers them."
Park in Brazilian state of Minas Gerais, where a group of marmosets live. (Photo: Marina H. L. Duarte)
During the week, the edges of the park can be as loud as a dance club, Young said, and on Sundays a recurring street fair and visitors will drive up the noise level in the interior of the park to 74 decibels.
The monkeys inhabited the quietest areas of the park, moving as the noise levels changed. These quiet areas happen to contain fewer of the park's fruiting trees, the monkeys' favorite food source.
"In the wild they stay close to the food, since they need food to survive. In the park they don't stay close to the food," Young told LiveScience. "They spend most of the time in the center of the park, which is the quiet area. They make infrequent trips to the edges to eat."
Marmoset in the park. (Photo: Teresa Young)
"The other possible reason is that the noise interferes with their ability to communicate," Young said.
Some of Young's unpublished work suggests the latter, showing that the animals in these city parks use calls of different frequencies to communicate with each other, and use these calls about 10 times less than their wild counterparts. That research has yet to be peer-reviewed.
Young's research group is continuing to study the effects of noise pollution on wild animals, including the noise caused by mining operations in the forests of Brazil.
The study was published June 28 in the Journal of the Royal Society Biology Letters.