The tamarin on Brazil’s R$20 note once had only around 200 left in the wild; Smithsonian zoologist Devra Kleiman helped build the breeding program behind its recovery

Look closely at a Brazilian 20-real note, and you'll see a little monkey with a fiery orange mane staring back at you. The golden lion tamarin is one of Brazil’s most recognizable animals, as a Mongabay feature on the species notes. But by 1972, the Smithsonian Institution Archives reports, its wild population had fallen to around 200 individuals, and the species was on the brink of extinction. A newly hired research zoologist named Devra Kleiman set out to change that.

When there were only 200 left

Despite weighing only half a kilogram, the golden lion tamarin has an impressive mane that resembles that of a miniature lion. It is found only along Brazil’s Atlantic coast, in a rainforest that once stretched for thousands of kilometers. Deforestation, farming, and urbanization over several centuries destroyed much of that rainforest and reduced the tamarin population. By 1972, golden lion tamarins in captivity were barely reproducing, and the wild population had dwindled to around 200 animals, so small that too few mates, too little genetic variety, and a single bad year could have eliminated the species for good, according to the Smithsonian Institution Archives.


The zoologist who took on the impossible

That year, Devra Kleiman, newly hired at the Smithsonian's National Zoological Park in Washington, D.C., established what would become the Golden Lion Tamarin Conservation Program, according to the Smithsonian's own archives. Her first job was to get more tamarins to breed successfully in captivity. Her team discovered through years of trial and error that feeding the animals more protein sharply increased birth rates in captivity, the archives report. Within 10 years, zoos had more golden lion tamarins than the breeding population could support.

Building a program built to last

Breeding the animals within the zoo enclosure is one challenge, while raising the offspring within a natural forest environment is another. Through the 1980s, the program built out long-term field research, community education programs, and a formal reintroduction system, first within the reserve and then on neighbouring private land. Primatologist Maria Cecília Kierulff and colleagues describe this evolution in the 2012 study titled 'The Golden lion tamarin Leontopithecus rosalia: a conservation success story,' published in International Zoo Yearbook. About 30 zoos around the world eventually contributed 146 captive-born tamarins, along with research on the animals' behaviour, nutrition and health, the study says.

The long trip home

The Poço das Antas Biological Reserve, located in Rio de Janeiro, Brazil, was founded in 1974 for the purpose of giving the species a place where it could safely return, the Mongabay report notes. However, it took about another decade before the first zoo-bred tamarins were able to make that journey. In November 1983, 15 zoo-bred tamarins were transported from the United States to Brazil, quarantined, and held temporarily in a transitional outdoor enclosure within the reserve itself, to acclimate to the trees, insects, and predators before being set fully free. Eight of them were released into the reserve on July 25, 1984, Smithsonian Institution Archives records. It wasn’t a smooth ride at first; several died, and caretakers had to keep putting food in. But two females soon produced offspring in the wild, and their young adapted much better than their parents.

From 200 to thousands, but not out of the woods

Reintroductions were carried out year after year, and as the program learned from its mistakes, survival rates improved. By 2019, the wild population had increased to approximately 3,200 golden lion tamarins, one-third of whom were descended from captive-born ancestors, according to the Smithsonian Institution Archives. That’s a real turnaround from 200 animals, but it is not over yet.

The Atlantic Forest is still badly fragmented today into small disconnected patches of trees, Mongabay’s reporting notes, and conservationists are now focused on building forest corridors to reconnect them, since isolated pockets of tamarins still face the same genetic risks that almost finished the species off decades ago.

Why a story about a little monkey matters to us

It’s easy to scroll past extinction stories, because they often don’t end well. This one did. A scientist identified the problem, spent years studying the species, and helped build a conservation system that reversed the decline. It took different zoos on different continents, Brazilian researchers on the ground, and decades of unglamorous, careful work, no one dramatic rescue moment, just a slow rebuild that eventually paid off. The golden lion tamarin is not safe yet. But it is alive, breeding in the wild and on the currency millions of Brazilians carry with them every day.