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Secrets of Goeldi's Monkeys Revealed

The secret lives of South America's "mystery monkeys" are finally coming to light. Goeldi's monkeys (Callimico goeldi) are small South American primates, and their unusual anatomical, behavioral, and reproductive traits have long been a source of confusion for taxonomists and physical anthropologists. C. goeldi was even postulated to be the missing evolutionary link between small and large New World monkeys.

But in June 2004, results from the most detailed study on the ecology and behavior of the animals to date were published in the journal Evolutionary Anthropology, indicating that this is not the case.

Discovered by the Swiss naturalist Emil August Goeldi in 1904, C. goeldi is now an endangered species in the wild. The mystery of these monkeys, enhanced by their endangered status, stems primarily from the difficulty of observing them in the wild, according to Leila Porter, a biological anthropologist at the University of Washington, and co-author of the recent report.

She studied Goeldi's monkeys in the Amazon basin of northern Bolivia for four years. However, she notes, the monkeys are so timid and elusive that she was able to observe them for a total of only about one minute during her first three-month visit to Bolivia. Extended fieldwork changed that, but even so, her studies revealed that Goeldi's monkeys never followed before take at least five months to become habituated to humans. Only after that time would they tolerate being trailed and observed by researchers in the forest throughout the day.

Unlike their marmoset (Callithrix and Mico), tamarin (Saguinus), and lion tamarin (Leontopithecus) relatives, which are often brightly colored and have showy features, Goeldi's monkeys are all black. Weighing about a pound, they stand nearly nine inches tall and have a tail that extends another foot. They live primarily below 10 meters (33 feet) in the understory of the Amazonian rainforest in Bolivia, Brazil, Columbia, Peru, and Ecuador, but no one knows exactly how many exist. Large hands with claw-like nails help them leap from tree to tree and walk on four limbs along the tops of tree branches. They travel in groups with an average of six members.

Goeldi's monkey gives birth to a single offspring twice a year, while marmosets and tamarins give birth to twins either once or twice a year. There is usually only one breeding female per group, but like their close primate relatives, Goeldi's monkeys engage in cooperative infant care by sharing food and carrying infants on their backs.

C. goeldi subsist largely on fruit and sometimes grasshoppers, but Porter found that they also eat fungi growing on bamboo and rotting wood as a supplement during the dry season when fruit is scarce. These observations make them the only tropical primate species known to subsist on this food source for part of the year.

Despite the unique characteristics Porter observed, she and co-author Paul Garber, a biological anthropologist from the University of Illinois at Urbana-Champaign believe that Goeldi monkeys' behavior, ecology, and anatomy fit within the diversified adaptive radiation of marmosets and tamarins. This suggests that the monkeys do not represent a missing link between large and small New World monkeys, so much as an interesting example of adaptation as a group of animals diversifies to fill different ecological niches.

Sources: University of Washington, Evolutionary Anthropology 13:104-115 (2004).