In a vulnerable forest in southeastern Brazil, where the air was once thick with the guttural chatter of brown howler monkeys, there now exists silence.
Yellow fever, a virus carried by mosquitoes and endemic to Africa and South America, has robbed the private, federally-protected reserve of its brown howlers in an unprecedented wave of death that has swept through the region since late 2016, killing thousands of monkeys.
Karen Strier, a University of Wisconsin-Madison professor of anthropology, has studied the monkeys of this forest since 1983. She visited the reserve -- her long-term study site near the city of Caratinga -- in the state of Minas Gerais, in January of 2017. "It was just silence, a sense of emptiness," she says. "It was like the energy was sucked out of the universe."
Using what in some cases are decades of historical data, Strier and a team of Brazilian scientists focused on studying primates in Brazil's patchwork Atlantic Forest are poised to help understand and manage what happens next. They have never seen monkeys perish in such numbers, so quickly, from disease.
With her Brazilian counterpart Sérgio Lucena Mendes, a professor of animal biology at the Universidade Federal de Espirito Santo, and their former postdoctoral researcher, Carla Possamai, Strier is ready to census the monkeys that remain at the reserve, comparing the new data to prior censuses performed in the forest. They also plan to study how the surviving brown howler monkeys regroup and restructure their societies, since their existing social groups have been destroyed.
Strier's study forest, just 4 square miles in size, is a land-locked island of green surrounded by agricultural and pasture lands. How yellow fever showed up here is a mystery, and the monkeys in the forest have nowhere else to go. Less than 10 percent of Brazil's Atlantic Forest remains intact and much of it exists only as small patches in a fragmented landscape.
"I am very surprised at the speed with which the outbreak is advancing through the landscape and by how the virus can jump from one patch of forest to another, even if they are hundreds of meters apart," says Mendes. "It is also surprising that it is spreading across such a large geographic region."
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