Planet Earth

Brazilian Rendezvous: Convincing Critically Threatened Monkeys to Mate

Primatologists devise ways to revitalize the population of Brazilian tamarins.

By Mary C PearlNov 1, 2006 12:00 AM


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Few creatures on Earth are as cute as the black lion tamarin, and few have as dramatic a story line. Pug-nosed and diminutive, with a comic fringe of hair, these monkeys dwell in trees in small tracts of forest in southeastern Brazil. Or they did until 1905, when they were declared extinct. No one saw a black lion tamarin again in the wild until 1970, when the great Brazilian primatologist Adelmar Coimbra-Filho came across a tamarin family in a little reserve in the far western corner of São Paulo State. Later, in the 1990s, researchers turned up a small set of isolated, inbred populations scattered over a wide region. Since that time, the Brazilian team of Claudio Padua and Cristiana Martins of the Institute for Ecological Research has been engineering tamarin migration and mating, doing everything they can to bring back to health one of the world's most distinctive primates.

Although they are no larger than house cats, tamarins have brains that are surprisingly big for their size and a family life organized like our own. They live in groups anchored by an adult male and adult female, along with some younger animals, including their offspring, and an occasional male from a neighboring group. When a mother bears young, she usually produces twins, and although members of the group share in their upbringing, it is most often the father who carries them around in the trees, where the families feed on fruits, insects, lizards, and birds' eggs.

A simple solution was to build bridges across roads, allowing the monkeys to move from one forest to another. With some lumber and a day's work by Padua and his colleagues, habitats that had been separated became continuous again, improving opportunities for migrating and mating.Unhappily for the lion tamarins, their tree-bound niche began to disappear after the Portuguese landed in Brazil and began clearing forest to make room for Rio de Janeiro, São Paulo, and the many settlements and farms of southern Brazil. As is the case for so many threatened species, the breakup of their habitat sounded the death knell for tamarins, depriving them of the continuity of forest they require to remain abundant and safe from potential threats in any single vicinity. The animals avoid predators by hardly ever coming down from the trees, so even a narrow logging road through a forest can begin the breakup by preventing them from moving from one patch of forest to another.

The next step was to broaden the distribution of the population. Padua and his team captured a family of black lion tamarins in the Rio Claro Farm (a forest managed by the timber company Duratex) and moved them to forest where black lion tamarins formerly lived. The first group consisted of an adult pair and a young male and infant daughter. The second had an adult pair, another adult male, one adolescent male and a female, and an infant son. After a year, the moves were declared a success: Not only had 80 percent of the tamarins survived, but they had also produced new offspring. The young adult male of the second group left his birth family and successfully entered the other recently translocated group.

So far, so good. The black lion tamarin recovery team had learned that the animals could adjust to the new forest, even if the insects there tasted a little different or the trees were a slightly different size. Still, the problem of limited gene flow in a small population remained. As tamarin numbers dwindled, the population had lost the genetic diversity that holds the key to resilience to various threats, like being able to withstand droughts or infectious diseases.

The number of black lion tamarins in the wild had fallen to fewer than 1,000, with most isolated fragments hosting well under 100 monkeys. In a population with so few individuals, an unhealthy mutant gene will more often find itself paired with the same mutant gene in an offspring because the parents are related and of similar genetic makeup. This double dose reduces the offspring's chances of surviving and reproducing, further reducing the species' chance of survival.

A tantalizing solution was to take advantage of the 100 or more captive black lion tamarins in zoos and primate centers. Their genetic diversity could replenish inbred populations in the wild, but how would the researchers get the genes of the captive animals into the wild? Putting into the wild animals adapted over generations to being fed and protected at zoos would be both cruel and ineffective.

Leave it to the Brazilians to provide a solution at once creative and romantic: Padua and Martins captured two wild young female adults from Morro do Diabo State Park, which with over 800 animals has the largest tamarin population, and introduced them to three captive-born adult males brought from the Jersey Zoo in England and the primate center in Rio de Janeiro. After three-week honeymoons, the animals were then set free in the Morro do Diabo forests. The mixed-marriage couples together faced the challenges of finding food and shelter, establishing a territory, and reproducing.

They got along well enough—at first. The researchers observed the animals copulating, although no births resulted. After three and a half months, the first captive-born male was eaten by an ocelot, the second one was preyed upon after five months, and the last one disappeared after seven months. It seemed that the imported males could learn how to find food and shelter from their native partners, but not how to avoid predators. They all died before they were able to reproduce successfully in the wild.

Perhaps the captive males should have merely honeymooned with the local females and skipped the partnership in the wild. The next rescue operation that Padua envisioned would be to capture whole families, separate the adult females, and entice them to have a sexual dalliance with exotic males from the Jersey Zoo and the primate center in Rio. In the meantime, to ensure that they didn't find other partners, each wild-male mate would have to cool his heels in captivity. Then each female, once pregnant, would rejoin her native family to settle down once again with Mr. Wild-Born Right—if, that is, he would have her.

Martins and Padua were making plans for such encounters when a more urgent—and happy—need arose. When several new populations of black lion tamarins were discovered in central São Paulo State, Padua and his team realized they needed to concentrate on saving the newly discovered populations, totaling about 100 individuals, because they were all living in precarious situations. This short-term crisis is taking precedence, but the longer-term crisis of inbreeding will require attention too.

The good news is that researchers have learned that moving the tamarins into new habitats can work, but that introductions of captive animals into the wild do not. This information will help when researchers try once again to introduce new blood into the tamarin population.

The techniques for saving species in the wild vary. Species with less stringent habitat requirements, like the Arabian oryx in Oman and the white rhinos in South Africa, have been rescued by moving animals into new settings as well as outlawing their killing. In the United States, wild turkeys are rebounding because of hunting bans and because forest cover is expanding across the Northeast. More challenging to preserve are species that require a lot of land, like elephants, and species that have highly specific requirements for habitat and prey—and a poor public image—like black-footed ferrets.

Ultimately, as in all challenges, knowledge is power. Armed with the numbers and the distribution of a species, as well as a thorough understanding of the conditions it needs in order to thrive and reproduce successfully, we can, with enough resources, intervene to save wild species from extinction.

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