One of the world’s most spectacular primates has become a symbol of conservation in Brazil, where an overpass is being built over a major highway to keep the species going.

The golden lion tamarin, one of the world’s most charismatic primates, has a dark face that can look inquisitive, challenging, almost human, framed in an extravagant russet mane.

The endangered New World monkey weighs less than two pounds. It lives only in Brazil, and only in the Atlantic coastal forest there. Tamarins spend their time high in the trees, up to 100 feet off the ground, in small groups of up to eight or so animals, with one breeding pair among each group.

The golden lion tamarin has always had its human admirers, many of them in the Old World. Europeans imported the animals as pets in the 1500s, and they can be seen in portraits of Spanish royalty.

They sleep at night and are active in the day, eating anything they can get their hands on — fruits, insects, small reptiles and amphibians. They have a life span of about eight years.

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But deforestation, agriculture and development destroyed much of its habitat, as the pet trade continued into the 20th century. By the 1970s, only about 200 animals survived.

Image The BR-101 highway in Brazil, which passes along the Poço das Antas Biological Reserve. The highway’s route cuts through chunks of Atlantic forest.

Image Golden lion tamarins in a forest preserve on private property in Casimiro de Abreu, southeastern Brazil.

Image Carlos Alvarenga, a forestry engineer, pointed at areas currently being restored to connect forest fragments in which the endangered golden lion tamarin circulates.

In 1992, the Golden Lion Tamarin Association (Associação Mico-Leão-Dourado) was founded in Brazil. In concert with international conservation groups and supported by a dedicated U.S. charity, Save the Golden Lion Tamarin, the group began to buy up land to create connected conservation areas. And zoos around the world, like the Smithsonian’s National Zoo in Washington, D.C., contributed to reintroducing the animals to the wild.

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The population had reached 3,700 in the wild, according to Luis Paulo Ferraz, the director of the association, but suffered its first population decline last year, when yellow fever killed hundreds of the tiny monkeys. There is no indication yet that tamarins are susceptible to the novel coronavirus, which is present in Brazil as in the rest of the world, but other primate species, like macaques, can become infected with it, according to laboratory reports.

Today there are about 2,500 tamarins living in about five million acres of forest. But only some of those forest acres are connected. In 2018, the largest block of connected land was less than 70,000 acres with less than 300 animals.

Image Andreia Martins, a biologist and leader of the metapopulation team at the Golden Lion Tamarin Association.

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Image Tamarins are omnivorous, diurnal and have a life span of about eight years. Scientists estimate about 2,500 remain in the wild.

Image Ademilson de Oliveira, a research assistant with the Golden Lion Tamarin Association, used a directional radio to track tamarin groups near a forest fragment in Casimiro de Abreu.

“Our main goal,” Mr. Ferraz said, “is to create a viable population in the long term.” What that means in numbers is a population of 2,000 tamarins with a connected conservation area of 2.5 million acres, milestones the group hopes to reach by 2025. Scientists say such a size is necessary for the population to be self-sustaining.

One challenge to getting connected areas was the widening of a major coastal highway, BR-101, which cuts through large chunks of Atlantic forest. The improvement of the highway created a barrier that isolated several forest areas and their more than 700 tamarins from three other large forest fragments.

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After negotiations and lawsuits, the conservationists managed to get the construction company to agree to build and pay for a forested overpass for animals, the first in Brazil, with a tunnel and forest canopy connections, to enable the tamarins and other animals to pass from one side to the other. The overpass is now nearing completion and should be done this year, Mr. Ferraz said.

Image Plans for the bridge in a construction office.

Image The land bridge took years to negotiate with the state, and is expected to be completed this year.

Image A construction worker in one of the underground corridors intended to allow animals to pass underneath the highway between forest fragments.

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His organization is working on planting to create forested conditions on both sides of the overpass, as well as on the overpass itself, to ease the transition for the tamarins and other animals. “We have been engaging small farmers,” Mr. Ferraz said. “We are working a lot in terms of forest restoration.”

Image Miriam Meireles de Oliveira, a farmer in Silva Jardim, works in greenhouses to grow native tree species that will be used in restoration efforts in the region.

Image A planting day in Casimiro de Abreu, one of several local farms where farmers convene each week to plant native species for reforestation and agricultural purposes.

Image The bridge, the first of its kind in Brazil, will serve many other species, helping join several forest fragments.

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As with many other conservation campaigns, the golden lion tamarin is the beloved and beautiful poster animal for the preservation of a habitat that includes many plants and less compelling animals, like sloths and frogs. The forest also provides a watershed for human use.

“We are not only talking about one species,” Mr. Ferraz said. “We are talking about the environment.”

But that one species, with its flaming fur, is irresistible.

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James Gorman is a science writer at large and the host and writer of the video series “ScienceTake.” He joined The Times in 1993 and is the author of several books, including “How to Build a Dinosaur,” written with the paleontologist Jack Horner.

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