Population of Brazil's endangered golden monkeys bounces back following yellow fever outbreak

There are now more golden lion tamarins bounding between branches in the Brazilian rainforest than at any time since efforts to save the species started in the 1970s, a new survey reveals.

Once on the brink of extinction, with only about 200 animals in the wild, the population has rebounded to around 4,800, according to a study released Tuesday by the Brazilian science and conservation nonprofit Golden Lion Tamarin Association.

"We are celebrating, but always keeping one eye on other threats, because life’s not easy," said the nonprofit’s president, Luís Paulo Ferraz.

Golden lion tamarins are small monkeys with long tails and copper-colored fur that live in family groups led by a mated pair. Usually, they give birth annually to twins, which all family members help to raise by bringing them food and carrying them on their backs.

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The monkeys, which live only in Brazil’s Atlantic Forest, are still considered endangered.

The population survey was conducted over roughly a year. Researchers went to specific locations and checked whether monkeys responded to recordings of the tamarins’ long call, which basically means "I’m here. Are you there?" said James Dietz, a biologist and president of the U.S.-based nonprofit Save the Golden Lion Tamarin.

The new population figures are notable because the species had experienced a sharp decline from a yellow fever outbreak. In 2019, there were 2,500 monkeys, down from 3,700 in a 2014 survey.

Scientists intervened by vaccinating more than 370 monkeys against yellow fever, using shots adapted from a formula for humans — a fairly novel approach for conservation.

Scientists "cannot pinpoint a single exact cause for the recovery," but believe several factors may be at play, said Carlos R. Ruiz-Miranda, a State University of Northern Rio de Janeiro biologist who advised on the population study.

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Firstly, the yellow fever outbreak has subsided, perhaps due to a combination of the virus’ natural cycle and the vaccination campaign.

The animals may also be benefiting from an increase in forest habitat, said Dietz, who is also a research associate at the Smithsonian Institution’s Conservation Biology Institute. Between 2014 and 2022, the amount of connected forest habitat increased 16%, mostly through forests regrown on converted cattle pasture, he said.

Currently about three dozen farmers and ranchers in the Atlantic Forest region participate in such reforestation programs.

"It makes me so happy to see the tamarins playing free on my farm. They don't only live in protected areas," said Ayrton Violento, a farmer and entrepreneur in the small city of Silva Jardim. His family's Fazenda dos Cordeiros has planted native fruit trees and also manages a tree nursery for native Atlantic Forest seedlings to plant on other farms.

"Recently, every year I see more tamarin families, more frequently," he said.

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Ferraz, of the nonprofit Golden Lion Tamarin Association, said that despite the good news, he was still concerned about a renewed risk of trafficking for the illegal pet trade. The problem was rampant in the 1960s, but had almost disappeared in recent decades due to enforcement.

In July, the anti-poaching nonprofit Freeland Brazil reported that Suriname's forest service had seized seven golden lion tamarins and 29 endangered Lear's macaws believed to have been trafficked from Brazil for sale in Europe.

"We have seen the resilience of the species, but also know they are still vulnerable," said Ferraz.

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