A look back: 40 years after the first GLT reintroductions

Almost 40 years ago, on May 31, 1984, a family group of eight golden lion tamarins that had been born in a wild animal park in Kings Island, Ohio was released from an acclimation cage into the forest in the Poço das Antas Biological Reserve near Rio de Janeiro, Brazil. It was the start of reintroducing zoo-born GLTs into the wild.

Over the following 16 years, a total of 146 captive-born golden lion tamarins were reintroduced to the species’ native habitat in Brazil. Before coming to Brazil, those captive-born GLTs had been born at or lived at the Smithsonian’s National Zoo, the Rio de Janeiro Primate Center, a research colony at the University of Nebraska, and 40 other North American and European zoos.

Two golden lion tamarins born in captivity begin to explore their natural habitat in Brazil in 1984. (Photo credit: James Dietz)

The reintroduction of captive-born primates into the wild was an uncommon practice at the time. Many say the actions taken 40 years ago saved GLTs from extinction in the wild. The GLT reintroduction also served as a model for reintroductions of other species into the wild. 

The reintroduction efforts also brought national and international media attention, giving local residents a sense of pride and purpose, said James Dietz, a conservation biologist who helped coordinate studies of native GLTs in Poço das Antas and, who along with his wife Lou Ann, helped initiate the Golden Lion Tamarin Conservation Project starting in 1983.

“GLTs became the icon for nature conservation in Brazil,” James Dietz said.

The small monkeys, native only to Brazil, were on the brink of extinction in the 1960s, with the wild population estimated to be between 200 and 600 individuals. Deforestation for timber and charcoal production, agriculture, and cattle ranching, followed by urban expansion, devastated the tamarin’s habitat, reducing it to only 8% to 23% of its original area, fragmented in small islands of mostly regenerated vegetation. 

By 2000, the reintroduced captive-born population and their descendants had grown to 359, with 341 of those GLTs having been born in the wild. Additionally, through the engagement of local landowners who allowed GLTs to live protected on their properties, about 3,000 hectares of forest, or about 7,413 acres, had been protected as a result of the reintroduction efforts.

Fast forward to today and a recent population census shows the total number of GLTs in the wild is 4,800, of which more than 2,500 are descendants of the original reintroduced GLTs. Additionally, reforestation efforts over the years to help consolidate and connect several isolated blocks of GLT habitat are resulting in significant progress toward achieving a science-based goal of at least 2,000 GLTs in 25,000 hectares (61,776 acres) of connected forest. That goal is based on maintaining a genetically and demographically healthy population necessary to keep the species from extinction. 
To reach that goal, Brazil’s Associação Mico-Leão-Dourado (AMLD) is planting a native-forest corridor joining two large tracts of forest. Jennifer’s Forest Corridor, named in honor of SGLT director Jennifer Mickelberg who passed away in October 2023, will result in over 2,200 GLTs in connected habitat, exceeding Jennifer’s definition of a minimum viable GLT population.

Several of those leading the reintroduction efforts in the early years say there were many successes and disappointments as captive GLTs began living in the wild. Several of these trailblazers recently reminisced about that pivotal time.

Before reintroductions

Critical planning took place among multiple institutions across dozens of countries before any GLTs were reintroduced into the wild. Benjamin Beck, then Associate Director for Animal Programs at the Smithsonian’s National Zoo, served as the golden lion tamarin reintroduction coordinator. He relied heavily on the collaboration of many National Zoo colleagues, including Devra Kleiman and Lou Ann and James Dietz. 

Other collaborators included financial supporters, Brazilian collaborators, graduate and undergraduate students, Brazilian wildlife protection officials, zoo staff, researchers and many others, Beck said.

Working out of an abandoned farm house in the Poço das Antas Biological Reserve that Lou Ann and James Dietz rehabilitated, a team prepared for the arrivals of zoo-born GLTs. 

One team member, Inês Castro, had grown up in São Paulo, Brazil, but had never seen or heard about golden lion tamarins. Castro, who had recently graduated with a biology degree, worked with the GLT conservation team to observe groups of captive-born GLTs who were in quarantine in Brazil as part of the reintroduction program. 

Inês Castro, in Brazil in 1984, holds a platform built with hidden food so reintroduced golden lion tamarins could learn to search for food in their natural habitat. (Photo Credit: AMLD archives).

Castro remembers she kept a log of what the monkeys ate, when they slept, how they interacted with each other and other behaviors. Periodically, the team would reposition branches in the cages or hide food inside a banana leaf to encourage the GLTs to navigate and learn from new challenges. Those behaviors were also recorded.

After six months of observations, the team built the large wire enclosure in the forest as the next step in the reintroduction process.

Beate Rettberg , Ben Beck and  Inês Castro observe captive golden lion tamarins at the Center for Primates of Rio de Janeiro in Brazil in 1984. (Photo Credit: Golden Lion Tamarin Conservation Program / SGLT archives)

An ‘option of last resort’

After getting the GLTs acclimated to the wire enclosure for a few weeks, it was time to open the door for the animals to live in the wild. 

“The press was there, cameras at the ready, researchers taking data,” James Dietz said. “After a long time, the first two GLTs came out through the trapdoor, looked around and began to tentatively explore the forest — a rewarding moment for all of us,” James Dietz said.

The zoo-born animals had some difficulty in the wild. They struggled to maneuver through the natural vegetation and they didn’t have the natural instinct to defend against predators because they never had any at the zoo. Of those eight GLTs released in May 1984, six disappeared within the first year.  

“But two lived, reproduced in the wild, and launched us on a path of births and deaths, success and challenges, and changes in methodology that have led to a wild golden lion tamarin population in the thousands, of which more than a thousand are descendants of reintroduced captive-borns,” Beck said.

Castro said it was difficult to see some of the zoo-born GLTs struggle with living in the wild. “It was very hard to see by everybody,” Castro said. “We had spent six, seven, eight months watching them, figuring out their personalities and then they’re gone.”

Andréia Martins, a native of the Silva Jardim community in Brazil, was also an essential member of the GLT reintroduction team and continues GLT conservation work with AMLD.  Associação Mico-Leão-Dourado. The Brazilian-based non-profit works with its sister organization, U.S.-based Save the Golden Lion Tamarin (SGLT) to protect golden lion tamarins and their forest habitat. James and Lou Ann Dietz, Castro and Beck are founding directors of SGLT.

Martins, who keeps track of individual GLTs through telemetry signals sent by the animals’ collars, can remember the names and parentage of 200 monkeys at a time, Beck said. In a 2023 profile, Martins said the team worked very hard to keep the animals healthy. For those zoo-born GLTs introduced into the wild, “they had to learn how to do things in the forest. We needed to teach them a little bit how to survive but their babies born in the forest, it’s easy for them to be wild.”

Reintroduction team members did not initially provide for the GLTs after they were released, assuming that they needed to survive on their own for the reintroduction to be successful. However, mortality was so high that the team switched to a soft-release strategy in which the GLTs were given food and water for at least six months after release, provided with an artificial nest box, rescued when they were lost, and treated for illness or injury. This resulted in higher survivorship and successful reproduction.

“The lessons are that reintroducing zoo-born primates is difficult and definitely does not reduce stress and increase well-being of the primates involved,” Beck said. “Reintroduction is a conservation option of last resort.”

Saving species and sharing knowledge

While much of the reintroduction work was taking place in Brazil, dozens of zoos and research institutions internationally collaborated to support the field work. 

Commitment to the conservation of GLTs began in the 1970s at the Smithsonian’s National Zoo under the leadership of Devra Kleiman. Around this time, the zoo formed a unique partnership with other zoos around the world to care for the captive and wild populations of GLTs. And in 1981, GLTs became one of the first species to be designated as part of the Association of Zoos & Aquariums’ Species Survival Plan (SSP) and the European Association of Zoos and Aquariums’ Ex-situ Species Population Management and Conservation Program (EEP). These plans help partners manage zoo species populations to be healthy, genetically diverse, and demographically varied among accredited zoos.

Toni Allen had recently retired as a Washington, D.C.-based lawyer when she began volunteering at the Smithsonian’s National Zoo in 2001. At the time, the National Zoo had a program that would allow GLTs to range freely in a section of the zoo to prepare them for potential participation in the reintroduction program in Brazil. The free ranging GLTs would move among the trees in the zoo during the day.

Allen was a behavior watcher at the zoo, following the free-ranging animals around the property and recording their movements and other activities. She also had to reassure zoo visitors that the GLTs were not lost but that they were playing a vital role in conservation of their species in the wild. 

“It’s important because they [zoo visitors] need to know what’s happening with these animals that were almost extinct and so it was important to educate them,” Allen said.

Although none of the GLTs Allen monitored participated in the reintroduction program, her involvement was the springboard to her long-term commitment to GLT conservation. “Having seen it succeed, I wanted to continue to see it succeed,” said Allen, who is now a board director of SGLT.

The intensive conservation efforts over the years led to GLTs being downlisted in 2003 from Critically Endangered to Endangered on the International Union for Conservation of Nature’s Red List of Threatened Species. 

Due to the early reintroduction efforts and conservation work done over the past four decades, the plight of the species is improving. However, diseases, such as the 2017 yellow fever outbreak, and illegal animal trafficking, continue to threaten the species and remind animal conservationists that there’s more work left to do.

“The golden lion tamarin conservation effort is an acknowledged, oft-cited conservation success story, at least so far,” Beck said.

A descendant of reintroduced golden lion tamarins in its forest home. (Photo Credit: James Dietz)