Good partners and great dads: insights into the world of owl monkeys

Since 1996, Yale anthropologist Eduardo Fernandez-Duque has studied owl monkeys — the only primate species in the Americas with nocturnal habits — in the wild at a field site he established in northeastern Argentina.

During those years, Fernandez-Duque has been part of a vibrant, growing international community of scholars that has revealed important insights into these once poorly understood animals, which range from Central America to Argentina.

This fall, Fernandez-Duque edited and published, “Owl Monkeys: Biology, Adaptive Radiation, and Behavioral Ecology of the Only Nocturnal Primate in the Americas” (Springer), a volume that synthesizes what scholars have discovered about owl monkeys, both in the wild and in captivity, over the past 30 years. The book’s 25 chapters — authored by 57 researchers representing 15 countries — cover a broad range of topics, including the monkeys’ behavior, physical characteristics, diet, genetics, geographic distribution, and conservation status.

“When I began my work on owl monkeys in the 1990s, owl monkeys were one of the least understood primates,” Fernandez-Duque says. “Since then, we’ve learned a lot through research initiatives in Colombia, Peru, Panama, as well my project in Argentina.”

In an interview with Yale News, Fernandez-Duque, who has appointments as professor of anthropology in Yale’s Faculty of Arts and Sciences and the School of the Environment, describes some of the owl monkeys’ more fascinating attributes — including their notably monogamous lifestyle and the males’ reputation as exceptionally attentive fathers — and some of the threats these animals face due to human activities. The conversation has been edited and condensed.

What makes owl monkeys unique?

Eduardo Fernandez-Duque: Aside from their nocturnal habits, male and female owl monkeys establish pairs, forming very emotionally strong and enduring relationships. Our research indicates that they are also genetically monogamous, they only reproduce with each other. And when the infants are born, the male parent becomes one of the most amazingly attentive fathers in the living world. There’s nothing like them among all mammals in terms of caring for their young. They’re great dads!

Also, they produce relatively loud, low-frequency calls that sound a bit like the hoot of an owl, hence the name.

What inspired you to assemble the book?

Fernandez-Duque: When I began my work on owl monkeys in the 1990s, owl monkeys were one of the least understood primates. Most of the research had involved owl monkeys in captivity. Knowledge drawn from wild populations was only beginning to emerge. Since then, we’ve learned a lot through research initiatives in Colombia, Peru, Panama, as well my project in Argentina, spanning the monkeys’ geographic range. Research on both captive and wild populations has continued developing. And we’ve amassed enough knowledge about owl monkeys to integrate it into a single volume. 

I’m very proud that most chapters are authored by researchers from countries where owl monkeys range. Editing the book has helped me to learn a lot about the excellent research that my colleagues are doing in the United States, Central America, and South America.

Owl monkeys range from Central America throughout South America. What ecosystems do they inhabit?

Fernandez-Duque: They live in a very wide variety of habitats. In Colombia, you find owl monkeys living at altitudes above 10,000 feet where temperatures get very cold. But you also find them in tropical rainforests within the Amazon Basin at sea level. In Argentina, they live in the Humid Chaco, where temperatures may range from below freezing in winter to over 100 degrees Fahrenheit in summer. They inhabit places that receive more than 118 inches of rain per year and places that get only a fraction of that amount. 

The diversity of habitats poses challenges when we try to formulate hypotheses about why owl monkeys behave as they do based on local ecology because while you’re studying them in a specific landscape you know that they are also living in completely different habitats. You must take this broad geographic distribution into account when explaining the evolution of their behavior.

Given that owl monkeys have such an extensive geographic range, how can we know that all species are monogamous?

Fernandez-Duque: In all the groups of owl monkeys that have been studied, there are only pairs of one male and one female who live and mate monogamously. But Argentina is the only place where we have genetic data that show they are only reproducing with each other. That said, owl monkeys are one of the few mammals where we have absolutely no evidence of unfaithfulness; there’s not a single genetic data point that suggests that males and females in pair relationships — who sleep together, feed together, move together — are not exclusively mating with each other.

Now, I’d be shocked if eventually we do not find some extra-pair relationships, but we haven’t yet. In Argentina, we’ve done paternity assessments of roughly 120 infants. And in every single case, the male in the monogamous pairing was the most likely sire. That is very unusual. We only otherwise see it with titi monkeys, which are the other pair-living group of monkeys, but the evidence is not as robust yet.

The book includes several chapters on conservation. What human threats are facing owl monkeys?

Fernandez-Duque: There’s a chapter led by my colleague, Angela Maldonado, who has been working for 20 years in Colombia, on the illegal trade of owl monkeys across the tri-border area of Colombia, Brazil, and Peru. The chapter focuses on a species, Aotus nancymaae, that has been heavily used for biomedical research, specifically malaria research. From a biological perspective, what is interesting about the research Angela and her colleagues have led is the question of whether we’re dealing with different species of owl monkeys. The thinking is that the Amazon River forms barriers between owl monkey species. But we find species in Colombia that are only supposed to live in Peru. One hypothesis is that locals in Peru are capturing owl monkeys and transporting them to Colombia. Once in Colombia, the monkeys end up in research centers where they are used in malaria research and then released into the wild nearby.

Sam Shanee, who directs an organization called Neotropical Primate Conservation, contributed a chapter on the conservation status of several species of owl monkeys in the Andes. As Sam explains, the primary threats to owl monkeys in that region are from farming, expanding human populations, mining, and logging. However, he suggests that protected areas and owl monkeys’ relatively small size, nocturnal habits, and behavioral plasticity, combined with the creation of protected areas, may help them survive.

You coauthored several chapters. What’s an example of one?

Fernandez-Duque: I wrote a chapter with my colleague Horacio de la Iglesia of the University of Washington that synthesizes all the work we’ve done over 20 years on the remarkable circadian biology of owl monkeys in Argentina. While owl monkeys are the only nocturnal primates in the New World, at least one species we study in Argentina, A.a. azarae, demonstrates remarkable plasticity in its activity patterns. These monkeys have periods of activity in the day as well as the night. We had previously published our findings in well-respected journals but had never sat down and made sense of everything we’d learned. Doing so was very satisfying.