By: Eduardo Fernandez-Duque, Ph.D

As I sit down to write this note, the image that comes to my mind is that of my first night in the forest two years ago. That night, I laid down on my back, stared at the full moon, a listened to the forest. I took a deep breath and felt that every creature, every leaf, every sound was welcoming me. I was about to start an ambitious and challenging project: a long-term study of nocturnal owl-monkeys (Aotus azarae) of Formosa, Argentina.
Owl monkeys, or Mirikinas, as they are called in Argentina, are small neotropical primates found from Panama in the north, to Argentina in the south.

Two characteristics of owl monkeys make them unique. First, owl monkeys are the only nocturnal primates that live in the neotropics. Although there are other nocturnal primates, ( e.g. the aye-ayes from Madagascar described in the summer issue of Positively Primates), they all live in Africa or Asia. Secondly, Mirikinas are one of the few primate species that live in small monogamous groups (2-5 individuals), usually composed of an adult pair, one infant, and sometimes a juvenile. Traditionally considered monogamous, owl monkey males and females believe to pair for life and remain sexually faithful to one another.

In 1996, I began “Proyecto Mirikina,” a long-term research program aimed at studying the behavior, ecology, and conservation of owl monkeys. After establishing camp at a cattle ranch in the Province of Formosa, Argentina, we began to work in collaboration with Argentinean students and Earthwatch volunteers. We established more than fifteen kilometers of trails through 70 hectares of forest. The trails had to be marked with fluorescent plastic tape to facilitate walking through the forest at night. After four months, we had identified 10 groups regularly using this area. Over a period of three months, we collected more than 300 hours of observation from five different groups. We observed them foraging, traveling, vocalizing, and mating during the day as well as at night. Their territories ranged between four and eight hectares.

Group size ranged between three and six individuals. Between April and October of 1997, we never observed a newborn or dependent infant in any of the groups. However, with the support of the DuMond Conservancy, three Argentinean students returned to the forest this past January to check for the presence of newborns, and found a new infant in five of the ten groups, confirming that births occur seasonally.

In the next few months, we will continue monitoring the groups and habituating them to our presence. In July, we will begin a 12-month study to examine in detail some of the ecological and environmental factors that may contribute to the very unusual pattern of activity characteristic of owl monkeys. We will also try to collect blood samples to examine the genetic structure of the population.

Studying the behavior of nocturnal monkeys poses some extra challenges to the already difficult task of finding and following monkeys as they jump and run through the forest. To improve the quality of the work and to make it more efficient, we need to use sophisticated night vision equipment. We also would like to capture at least one individual per group, and fit them with a radio-collar to facilitate locating and following the groups. The night vision binoculars and the radio collars are relatively expensive pieces of equipment, which we are currently seeking support for.

Dr. Fernandez – Duque wrote this article for Positively Primates several years ago.