Family of black lion tamarins receives a new home to avoid local extinction

“Welcome,” wished biologist Gabriela Rezende as soon as the black lion tamarins ran towards the forest. In less than a minute, the family had disappeared into the tree canopy, and only the sound of leaves could be heard as the primates passed by, going further and further. As witnesses to the release, only four blue transport boxes remained on the ground, their doors wide open, and a whole team with broad smiles, satisfied with how quickly the tamarins left to explore their new home. The joy mixed with the hope that the black lion tamarins had been given a second chance in San Maria, one of the remaining fragments of the Atlantic Forest in the countryside of São Paulo, where the species struggles against the risk of extinction.

However, this is neither the end of the story, nor the beginning.

San Maria Farm is a private property where the forest has been preserved as a Legal Reserve – the percentage of a property that needs to maintain native vegetation coverage under Brazilian law – of other private areas. It is a 515-hectare forest fragment. One of the few remaining in the Pontal do Paranapanema region, in the far west of São Paulo state. This is the habitat of the black lion tamarin (Leontopithecus chrysopygus), a small primate, endemic to the forests of São Paulo that, as Atlantic Forest itself, lost space for the growing occupation of what is now the most populous state in Brazil. This severe habitat loss is the main reason why the species is considered Endangered to the risk of extinction.

In San Maria, however, the black lion tamarins endure alongside the forest. But not for long, at least not on their own.

The release of a group – the second one in a year – into the San Maria forest on the morning of January 18th was only one step in a long effort led by the NGO IPÊ (Institute of Ecological Research) to prevent this population of black lion tamarins, isolated in this fragment due to the deforestation around it, from disappearing and with it, its unique genetics, which are essential for the conservation of the species as a whole.

“In 2005, the population viability analysis already indicated that this population would go extinct in about 30 years due to its small size. And when I joined the project in 2013, we were already seeing that happen,” recalls Gabriela Rezende, project coordinator at IPÊ and the current leader of the Black Lion Tamarin Conservation Program, which has been working for 40 years to reverse the species’ extinction risk.

In 2013, recalls the coordinator, there were five groups and over 15 tamarins in the fragment. Almost a decade later, in 2022, only two groups remained. “We followed the population decline over these 10 years, and the prediction was coming true, and it raised a red flag that if we didn’t do something, soon we wouldn’t have tamarins left in the fragment,” Gabriela explains.

Losing the tamarins in San Maria is not just a matter of subtracting some individuals from the total count of the species – estimated at approximately 1,800 tamarins. Genetic studies done in 2003 with the tamarins from the fragment revealed that they had unique haplotypes, meaning their genes were not found in any other known population of black lion tamarins. This characteristic is what scientists call genetic diversity or variability, and it is considered a fundamental element for the health and maintenance of a population and a species in general.

“When there is a loss of genetic variability, it impoverishes and reduces the chances of the population surviving in the long term. It can interfere with reproductive success levels, with a lower birth rate, or with animals being born weaker, less able to withstand diseases,” explains the project’s veterinarian Daniel Angelo Felippi.

To prevent this population and its genetics from disappearing, there are two paths. The first, a long-term solution, is ecological restoration and planting forest corridors that connect the San Maria Farm with other areas where the black lion tamarin lives. The second, and more immediate solution, is translocating new groups into the fragment to maintain the genetic exchange dynamics among the animals.

In the species’ conservation effort, both strategies complement each other.

In 2019, IPÊ’s Restoration Program began planting a corridor of about 500 hectares, completed in 2023, linking San Maria Farm to another forest fragment, called Água Sumida, which is one of the four areas of the Mico-Leão-Preto Ecological Station, a federal protected area with 1,200 hectares. The expectation is that this corridor, which is currently in various stages of restoration, will expand the primate’s habitat and provide space and resources for the population to grow.

However, consolidating this forest to make it suitable for the tamarins takes no less than a decade. A time that, according to the analyses, the tamarins of San Maria did not have.

The numbers don’t lie: it’s time to act

To provide even more solid grounds for the proposed population management, reinforcing its necessity as the only possible solution to prevent local extinction, a new Population Viability Analysis model was developed. The work started in 2020 and the new model allowed the identification of priority populations for management and the strategies aimed at each of them.

The modeling, which includes new parameters related to habitat, such as climate change, fire risk, and resource availability, was built collaboratively by researchers from different institutions, including the National Center for Research and Conservation of Brazilian Primates (CPB/ICMBio) and IPÊ.

From CPB/ICMBio, the analyst Mônica Montenegro emphasizes that the model’s results confirmed the high risk of extinction for the population in San Maria Farm in about 20 years if no management was made. “Thus, the translocations carried out by IPÊ aim to prevent this local extinction of the species and, in the long term, establish a viable population in San Maria and neighboring fragments,” she adds.

“The model clearly indicated and scientifically proved that we needed to carry out the translocation [in San Maria], but to do that we also needed the involvement of the actors,” emphasizes Gabriela Rezende, who is one of the authors of the new modeling.

With the data on the table, the IPÊ team met with representatives from the federal environmental agency responsible for fauna management, ICMBio, and the state agency in charge of protected areas in São Paulo, Fundação Florestal, as well as various researchers to create the Integrated Black Lion Tamarin Population Management Program, which was approved in early 2024.

The program sets out guidelines, criteria, and a strategy for management actions, including translocation, aimed at the conservation of the species.

“Several of the program’s activities will assist this and other management actions, whether it’s in updating population viability analyses and identifying populations and areas that need population management intervention (population reinforcement or reintroduction); in analyses to define the minimum number of individuals or groups to be managed in a given period, to ensure population viability; in the creation of protocols for various management situations; among others. In addition, the network of people involved in the program, with diverse expertise, has been crucial in decision-making, especially in emergencies,” explains the CPB/ICMBio analyst, who is part of the group of experts overseeing the program’s implementation.

In January 2024, a first group, consisting of five individuals, was translocated to San Maria. And a year later, a new family was brought in to reinforce the population in the fragment.

A new home, a new chance

It was still dark when the team, splitted into two cars, set off towards the Morro do Diabo State Park. The protected area, with nearly 34,000 hectares of Atlantic Forest, is the only known location with a viable long-term population of black lion tamarins. Estimated at around 1,100 individuals, it’s capable of recovering quickly from the removal of a single group, making it the ideal “source population” for translocation.

With only the car lights to break the night, the forest was a tangle of silhouettes passing by the window as the car crossed SP-613, a state highway that cuts the park in half. Our destination was to the north, and we left the main road for a smaller dirt road, then into another even smaller one, hidden beneath tall grass.

When the vehicles finally stopped, there was only darkness for a few seconds. The clock still hadn’t reached 5 a.m. We were at the edge of the northern section of the state park. Slowly, everyone turned on their flashlights, and the forest appeared. About 500 meters away, a family slept unaware that it was carrying within them the hopes for the species’ future in San Maria.

There is a reason for starting work at dawn. The tamarins have a habit of spending the nights in tree hollows. And to capture all the individuals of a specific group – something important to maintain the animals’ social cohesion – IPÊ’s field team developed the effective technique of “hollow extraction”. That is, capturing them directly from the hollow. To do this, the team must track the tamarins at dusk on the previous day, when they start heading toward their shelter, and confirm which location they’ve chosen for the night. Luck is a factor at this point, as it’s important to see if the monkeys are in an accessible spot for capture. After two nights of no luck, the good news finally came: “We have the hollow!”

The hollow in question was in the robust trunk of a native copaíba tree, about two meters off the ground. Inside, a family of four black lion tamarins, two adults – the main couple – and their two juvenile offspring. The presence of the young is one of the criteria for translocation, as they will be responsible for dispersing and forming new families with tamarins already living in San Maria, thus promoting genetic exchange.

With skill, José Wilson, or Wilsinho, as is known the field assistant who has worked on the project since 2003 with tamarin management and monitoring, began sealing off possible exit routes through other holes in the tree.

With everything ready, still in the dark, the capture began. One by one, with the expertise of someone who’s been doing this for decades, Wilsinho took each member of the group and, with the help of João Medeiros, field biologist for the project, placed them into individual cloth bags. Quickly, with all the tamarins secured, we headed back to the trail toward the car, where the monkeys were identified, weighed, and then transferred to a proper transport container for their final destination and new home. Three of them also received a radio collar for post-release monitoring.

The capture site to San Maria is less than 20 kilometers apart in a straight line. By car, the route is less direct, but by 8:10 a.m., we were at the fragment, further north. Twenty minutes and a short trail later, the blue transport boxes were wide open, and the black lion tamarins were exploring their new home.

From capture to release, three hours passed, two of which were spent just on the road. The team’s agility in making this handling time as short as possible is essential to reduce the animals’ stress upon arrival in the forest.

Concern about timing extends to the release period, which took place in the second week of January during the rainy season, meaning more food is available in the forest to ease the group’s acclimatization to the new place.

The work continues

Monitoring the animals after release is a fundamental step to confirm how successfully the group adapted to the new environment and to understand the dynamics of occupancy in the fragment. For this, researchers rely on a combination of technologies – radio collars, audio recorders, and camera traps – along with the field effort from the team.

In the first two months, the newly translocated group will be actively monitored in the field for at least two weeks each month, “following the group, identifying the home range, the sleeping sites, and installing camera traps in the most accessible hollows they are using,” explains Daniel Felippi, veterinarian and field coordinator for the project.

From the second to the sixth month, the effort will continue with seven days of monitoring per month. And after six months, the recapture campaign begins to assess the health status of the animals – such as weight, nutritional condition, and parasite infestation – and to replace the radio collars’ batteries, a crucial step for successful and continuous monitoring.

In the first translocated group, the batteries ran out earlier than expected, before the recapture could be done, and as a result, they disappeared from the researchers’ radar in July 2024. At that time, one individual had died, and the other two, the juveniles, had vanished, possibly following their natural movement of dispersing from the original group.

Perhaps the hardest part of population management work is accepting the risks and the loss. Just over a week after the second group release, on a Tuesday (28th), the monitoring team delivered the news that no one wanted to give: one of the individuals from the group, an adult female, was found dead on the forest floor. The body was collected for a necropsy. With no visible signs indicating the cause of death, such as injuries or malnutrition, the team must wait for the laboratory results – which should take at least a month – to see if they provide any answers.

“It’s a punch to the stomach, but it’s part of this population management struggle,” Daniel vents.

The remaining three individuals from the group – one adult male and a juvenile pair – continue exploring the fragment, as is expected at this early stage until they establish their territory. And they remain closely monitored by the project.

“I say that to work with management in Brazil, you need a lot of courage. It’s obvious that the last thing we want is to lose an animal, especially an endangered species, so everything we do is to prevent that from happening, but even knowing that an individual might die, we do this [management] knowing that this group could save a population of this species,” Gabriela reinforces.

The Future

The main threat to the black lion tamarin in Pontal do Paranapanema is the fragmentation of forests. With only a tiny fraction of its habitat still standing, the monkey relies on Atlantic Forest restoration and the creation of ecological corridors to ensure its survival in the long term. The animal is the flagship of IPÊ’s planting efforts, responsible for restoring already more than 4,000 hectares of the biome since 2002.

In the northern part of Pontal, where San Maria Farm is located, in addition to the corridor already planted connecting the fragment to the of the Mico-Leão-Preto Ecological Station, there are other planned or ongoing corridors to ensure the connection to other fragments north of Morro do Diabo and, in the future, to the park itself. There is another ecological corridor being implemented to the west of the protected area.

“When we finish restoring all of this and connect the fragments with the park, which has 33,800 hectares, we will have over 45,000 hectares connected. One of our goals here in Pontal is to have tamarins in all the forest areas that are being connected. And for that, we need to work with population management,” says Gabriela.

The work includes evaluating other translocations and even reintroducing tamarins in places where they have been locally extinct, as well as strengthening the captive population – currently with fewer than 100 individuals – so it can serve as a backup population in case anything happens to the animals in the wild.

“Out of the twenty locations where the species currently occurs, we only have one viable and self-sustaining population recognized. This means that the other 19 occurrence locations need to be cared for, and management is a strategy that can help them survive,” concludes the coordinator of the Black Lion Tamarin Conservation Program.