Eduardo Fernandez-Duque’s research while affiliated with Yale University and other places

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Publications (12)


Geographic Distribution of Owl Monkeys
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September 2023

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165 Reads

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7 Citations

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Eduardo Fernandez-Duque

The owl monkeys, genus Aotus, are among the most widely distributed of all platyrrhine genera. The 13 currently recognized taxa are found in Argentina, Bolivia, Brazil, Colombia, Ecuador, Panama, Paraguay, Peru, and Venezuela. They range from lowland tropical moist and dry forests to over 3000 m.a.sl. in the cloud forests of the Andes. Owl monkeys appear to be sufficiently flexible to persist in anthropogenically altered habitats and fragmented forest patches. Here we gathered 1,703 owl monkey localities from a wide range of published and unpublished sources, making the most comprehensive database to date. These records were used to map the distributions of all owl monkey taxa based on our current understanding of the genus. Our knowledge is still limited in many areas where records are lacking, and we caution that all species IDs and maps be treated as tentative until the wide-ranging employment of genetic testing is available.


Aotus: A Model to Synthesize Studies of Captive and Wild Primates

September 2023

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33 Reads

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10 Citations

While often placed in opposition to one another, integrating data from studies of captive and non-captive nonhuman primates enhances our interpretation of their natural behavior and biology. Aotus is an excellent example for how studies from captivity provide data that can be used to reinforce and complement findings from field studies and vice versa. We highlight how these differing data sets have enriched our understanding of the genus and describe recent studies of chemical communication, and natural life histories and demographics, that have synthesized data collected from both field and captive populations. These studies illustrate the benefits and importance of integrative research and how such studies can better inform our interpretation of data and enhance our understanding of Aotus. With the aid of long-standing captive and wild research populations, Aotus has become a model taxon for a synthesis of captive and fieldwork.


Dispersal: A Critical Life History Stage Influencing Populations, Social Dynamics, and Individual Fitness

September 2023

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27 Reads

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12 Citations

Natal dispersal, the movement of individuals from their birthplace to new areas in which they may breed, is an important aspect of life history that influences processes at the level of the individual, group, and population. This chapter takes a holistic approach by reviewing what is known about the entire process of dispersal in owl monkeys, from when and why they leave their natal group to what they do and where they go after dispersing. It also examines how dispersal patterns can inform our understanding of the evolution and maintenance of owl monkeys’ social organization, mating system, and parental care. While owl monkey dispersal strategies are highly variable, we identify some important common patterns. All individuals, both male and female, disperse prior to reproducing. Individuals also often “prospect” prior to permanently dispersing, and almost always spend some time as solitary floaters. While dispersed solitaries may occasionally engage in prosocial interactions, they typically face aggression from adults in established groups. Currently, nearly everything known about owl monkey dispersal comes from a population of Azara’s owl monkeys (Aotus azarae) in Formosa, Argentina. Expanding studies to other sites and Aotus species will generate a more multifaceted understanding of dispersal in pair-living primates.


Past, Present, and Future Use of Technology for Field Studies of Owl Monkeys

September 2023

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58 Reads

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15 Citations

Owl monkeys are small, elusive, and nocturnal, making them some of the hardest animals to survey and study in the wild. We summarize the use of traditional field methods as well as more recent technology that has improved opportunities for investigating the behavior, ecology, and population biology of these neotropical primates. Over the years, research on owl monkeys has embraced the use of night vision equipment; radiocollars; identification collars; animal-mounted activity recorders; handheld GPSs; motion-detecting, infrared camera traps; passive acoustic recorders; and automatic weather data loggers. Many of these technologies have been tested and used across countries, habitats, and species. Additional technologies, such as drones and thermal cameras, are also likely to play a valuable role in research on owl monkeys and other nocturnal mammals in the near future, particularly as these become cheaper and more readily accessible to the wildlife research community.


The Great Unknown: The Floating Stage as a Neglected Aspect of Social Systems

September 2023

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47 Reads

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12 Citations

In the last few decades, important advances have been made in the knowledge on the behavioral ecology of pair-living primates such as owl monkeys (Aotus spp.). With the growing understanding, researchers have become increasingly aware that populations do consist not only of established family groups but also of solitary “floaters”: dispersing individuals who travel (mostly) solitarily after leaving their natal (or previous breeding) group and before obtaining a breeding position. Floaters may have a profound impact on local operational sex ratios and, thus, population dynamics, with the subsequent potential to change natural and sexual selection pressures on pair-living and sexually monogamous taxa. Unfortunately, floaters are notoriously difficult to study, so assessments of their role on social organization and mating systems remain challenging. Floaters of different taxa experience different selection pressures and employ varying strategies. In owl monkeys, a combination of limits to group size and habitat saturation forces all maturing individuals to become floaters as subadults or young adults, such that floating is essentially a life stage in the species. The dispersal process is accompanied by increased tensions between adults and pre-dispersing individuals, probably due to various aspects of food and mate competition. Owl monkey floaters balance the need for prospecting with avoidance behavior toward groups, with whom they can engage in highly aggressive and potentially lethal interactions, by adapting their ranging behavior to spatial avoidance while seeking proximity at a temporal scale. Some fundamental aspects of floater biology on owl monkey societies (e.g., mortality rates, impact on population dynamics) are still poorly understood. We strongly suggest that floaters in all taxa where they occur are taken more consistently into consideration and efforts are undertaken to improve understanding of their impact on group and population dynamics, and of sexual selection.


Fig. 10.1 Owl monkeys follow Bergmann's rule and species that are found further away from the equator have larger body masses. Data are shown for Aotus trivirgatus (n = 20), A. lemurinus (n = 7), A. zonalis (n = 6). A. azarae boliviensis (n = 4), A. nancymaae (n = 32), and A. a. azarae (n = 40). (Modified from Fernandez-duque 2011)
Fig. 10.2 Photos of captive individuals (left) from the Amazon (left, A. nancymaae) and from the South American Chaco (right, A. azarae) showcasing some of the diversity in pelage and body size. A. azarae are found in relatively colder climates than A. nancymaae. Owl monkeys found in colder climates, either as a result of latitudinal or altitudinal effects, generally have thick, long, shaggy fur, while those found in warmer climates have shorter fur. (Photo credit: Samantha Abros, Team Aotus, DuMond Conservancy, Miami, FL, USA)
Fig. 10.3 Behavioral thermoregulation by posture and socialization. Left: A. azarae huddling (photo credit: Dr. Margaret Corley, Owl Monkey Project, Formosa-Argentina). Right: sketch of ball-like, head-down posture by A. trivirgatus. (Modified from Moynihan (1964)) explains the activity patterns of endotherms as a result of thermo-energetic costs (Hut et al. 2012; Riede et al. 2017; Van Der Vinne et al. 2014, 2015). As stated by the CTEH, endotherms benefit by scheduling periods of activity during the daytime (i.e., the warmest period of the 24-h cycle) because they save metabolic energy that otherwise would have been invested while being active during the nighttime when it is colder (Van Der Vinne et al. 2014, 2015). As such, the CTEH predicts that individuals experiencing high thermo-energetic costs can schedule their bouts of activity during the daytime (Hut et al. 2012; Riede et al. 2017; Van Der Vinne et al. 2014, 2015). Although most owl monkeys are strictly nocturnal, peaks of activity in A. azarae occur throughout the 24-h cycle; individuals of this taxon range from being active all throughout the night, to being active predominantly during dusk and dawn (i.e., crepuscularity), or during the daytime and the nighttime (i.e., cathemerality) (Erkert et al. 2012; Fernandez-Duque and de la Iglesia 2023 this volume; Link et al. 2023 this volume). The temporal niche plasticity in circadian activity shown by the Azara's owl monkeys of the South American Chaco may have contributed to mitigating the costs of thermoregulation and reproductive effort as this relatively new biome was colonized during the adaptive radiation of the genus. Most of the available data on the effects of ambient temperature on daytime activity come from multiyear studies of a population of wild cathemeral Azara's owl monkeys (A. azarae) in Formosa, Argentina, though there are some available data on species
Fig. 10.4 Seasonal changes in ambient temperatures (solid lines, right y-axis) and daytime foraging frequencies per 20-min focal observation (dotted line, left y-axis) of wild A. azarae from Formosa, Argentina. The figure summarizes 4985 20-min focal observations collected from 140 individuals over 13 years between 2001 and 2015 (Perea-Rodriguez et al. 2022)
What Owl Monkeys (Aotus spp.) Tell Us About the Dynamics Between Thermo-Energetics and Organismal Biology
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  • Full-text available

September 2023

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156 Reads

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9 Citations

Owl monkeys are found in a variety of ecosystems ranging from the highlands of Panama and Colombia, to the Amazon, and to the South American Chaco. As such, the only extant nocturnal primate in the Neotropics experiences contrasting thermal challenges throughout its distribution, investing metabolic energy in thermoregulation appropriately. Thermoregulation is metabolically costly and limits the amount of energy individuals have to search for food, shelter, and mates, directly affecting their survival and reproduction. As a result, these ~1 kg monkeys seem to have developed strategies to balance their high investment in thermoregulation. We present a summary and synthesis of research on the thermo-energetics of captive and wild owl monkeys and describe the morphological, physiological, and behavioral adaptations they have evolved across their wide geographic distribution. We conclude by proposing a unifying model for the role ambient temperature has in the evolution of these pair-living, sexually monogamous primates.

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Communication in Owl Monkeys

September 2023

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43 Reads

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11 Citations

Although studying communication among nocturnal primates is particularly challenging, decades of research provide sufficient evidence to recognize that communication between owl monkey pair mates, among group members, and with individuals outside of the group is based on a variety of visual, tactile, auditory, and olfactory signals. Owl monkeys have evolved specialized morphology to facilitate communication, including a vocal sac and well-developed glandular regions used in scent-marking. Several aspects of communication also show some degree of dimorphism, particularly vocalizations, chemical deposits, and glandular morphology. Communication within the group may facilitate cohesion, coordination, travel, maintenance of the pair-bond, and development of relationships between adults and their young, possibly also mediating dispersal behavior. On the other hand, communication with individuals outside of the group, accomplished through indirect vocal and olfactory signals, or direct signals when visual and/or physical contact with neighboring groups or floaters occur, may aid in mate attraction or home range defense.


Morphology, Systematics, and Taxonomy of Owl Monkeys

September 2023

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44 Reads

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11 Citations

Owl monkeys, genus Aotus, are distributed from Panama to the northeast of Argentina and from the highlands of the Andes to the Atlantic coast. They are relatively small arboreal platyrrhines (0.7–1.5 kg) that show no conspicuous sexual dimorphism in body mass, size, body proportions or coloration, and facial markings. They live in small groups of one reproducing pair of adults and some young; the adult male in the group provides consistent and frequent care to the infants. Aotus, the only primate genus in Central and South America with nocturnal habits, has evolved a number of derived adaptations for dim light vision. Their diet, including fruit, some structural carbohydrates and insects, is related to their broad, cebine-like incisors, relatively small, sexually dimorphic canine teeth, and molar morphology. The classification of Aotus at the family and subfamily levels and the number of recognized species and subspecies within the genus remain unsettled. Morphological studies consider the genus to have a close affinity to the Pitheciidae, whereas molecular studies consider that the affinity of Aotus is closest to the Cebidae. Aotus is a sibling species complex, making it difficult for researchers to distinguish species based on external phenotype. The early division of the genus into nine species organized into two groups based on their karyotypes, coloration of the neck, and their susceptibility to malaria has been refuted by several phylogenetic studies. Even though wide differences in chromosome number argue for the primacy of recent chromosome evolution among the Aotus taxa, some problems of karyomorphs to distinguish species need to be considered. Variable taxonomic views throughout the development of our understanding of the variability of Aotus have recognized the number of species of Aotus as being from 1 to 11. Presently, up to 11 species can be recognized based on phenotypes, chromosomes, and lately molecular biology; we provide here evidence of a natural hybrid based on A. brumbacki and another, closely related and undescribed species that would bring the number of species to 12.


The Social Life of Owl Monkeys

September 2023

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50 Reads

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12 Citations

The study of owl monkeys provides an excellent opportunity for understanding the behavioral correlates of pair-living, sexual monogamy, and cooperative behavior. However, the nocturnal habits of most Aotus species make it challenging to study their social behavior in the wild. An integrated approach combining research in the field, seminatural conditions, and the laboratory has advanced our knowledge of their social behavior. Owl monkeys’ social behaviors reflect high levels of cooperation within groups, whereas the recent documentation of a subpopulation of solitary floaters in Aotus azarae has prompted the investigation of the intra- and intergroup social dynamics from a new perspective. Intrasexual competition, and the behavioral, vocal, and olfactory mechanisms associated with it, surely influences the serial monogamous mating system of the genus. Reproductive adults are highly cooperative in the care of infants; females usually limit infant care to nursing, while males carry, play, groom, maintain proximity, and share food with them.


Temporal Niche Plasticity of Owl Monkeys

September 2023

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3 Citations

Owl monkeys are the only nocturnal primates in the New World and the only nocturnal anthropoids. They concentrate their activities during the dark phase of the 24-h cycle, with peaks of activity at dawn and dusk. This has been confirmed by observational studies of free-ranging A. nigriceps, A. a. boliviensis, A. a. azarae, A. vociferans, and A. miconax. While the species in the tropics are primarily nocturnal, at least one shows a remarkable temporal plasticity in its activity patterns. Azara’s owl monkeys (A. a. azarae) of the Argentinean and Paraguayan Chaco are cathemeral, showing bouts of activity during the day as well as during the night. This chapter reviews the research that we have done both in the lab and in the field to understand the ecological correlates of this unusual activity pattern and its possible underlying mechanisms.


Citations (11)


... There have been no taxonomic changes or new species' descriptions since the update of . The most recent review and appraisal maintains 11 species, one of them, Aotus azarae comprising three subspecies (Fernandez-Duque et al., 2023). These authors emphasize that it is difficult to distinguish species by phenotypical differences. ...

Reference:

Taxonomy and systematics of the Neotropical primates: a review and update
Morphology, Systematics, and Taxonomy of Owl Monkeys
  • Citing Chapter
  • September 2023

... The most intense form of sexual competition for pair mates appears to be related to "solitary floaters." Floaters are male and female individuals who have dispersed from their natal groups (usually when they are ∼3 years old) and range solitarily while trying to gain a breeding position by forcibly evicting and replacing a resident adult (Fernandez-Duque & Huck, 2013;Huck & Fernandez-Duque, 2023 suggesting that both sexes face high levels of intrasexual competition from floaters. Floaters mainly range in the borders of the home ranges of groups while avoiding their core areas. ...

The Great Unknown: The Floating Stage as a Neglected Aspect of Social Systems
  • Citing Chapter
  • September 2023

... Aotus brumbacki is an endemic nocturnal primate of Colombian Llanos. It is distributed in piedmont of Colombian Llanos, in gallery forest, Mauritia flexuosa swamps and lowland forest fragments (Defler 2010;Carretero-Pinzón & Defler 2019;Carretero et al., 2020;Shanee et al., 2023). It has been poorly studied despite its endemism and vulnerable status (Solano 1995;Vargas 2011;Carretero-Pinzón 2013;Carretero et al., 2020;Vargas-Gomez et al., 2023). ...

Geographic Distribution of Owl Monkeys
  • Citing Chapter
  • September 2023

... The Azara's owl monkeys (Aotus azarae) from Formosa, Argentina, are pair-living, sexually and genetically monogamous primates that, in contrast to other species of the genus which are strictly nocturnal, show cathemeral activity patterns (Fernandez-Duque & de la Iglesia, 2023;Fernandez-Duque, Juárez et al., 2023;Fernandez-Duque, Rotundo, et al., 2023;Ziegler et al., 2022). In the Argentina population they are seasonal breeders producing a single infant once a year, usually born between late September and December Fernandez-Duque et al., 2002). ...

Temporal Niche Plasticity of Owl Monkeys
  • Citing Chapter
  • September 2023

... We predicted that if inbreeding avoidance was the primary cause of dispersal, then dispersals would consistently occur before, or around, the time individuals reach sexual maturity (approximately 3 years). The variation in age at dispersal indicates that while some individuals of both sexes dispersed around the time they reached sexual maturity, others delayed dispersal for up to 2 years [67,72]. While 31% of individuals had an unrelated adult (i.e. a potential mate) replace a genetic parent, the remaining 69% resided in natal groups with only close kin until they dispersed. ...

Reproductive Ecology and Behavioral Endocrinology of Owl Monkeys
  • Citing Chapter
  • September 2023

... Only by studying wild animals in natural environments can we gain insights into selection pressures and evolved life history, with ageing (and its potential for plasticity) as a quintessential part. The study of ageing in animal models can be improved by bringing together complementary approaches in both wild and captive settings [24]. For instance, assessing the generalizability and validity of findings is essential for enhancing the translational value of ageing research in animal models, and these targets can be realized most effectively by integrating research from the wild and captivity. ...

Aotus: A Model to Synthesize Studies of Captive and Wild Primates
  • Citing Chapter
  • September 2023

... In the Argentina population they are seasonal breeders producing a single infant once a year, usually born between late September and December Fernandez-Duque et al., 2002). The species shows extensive levels of biparental care, with males carrying, grooming, and sharing food with infants more than females do Garcia de la Chica et al., 2023;). Azara's owl monkey groups are territorial, and, in Formosa, they actively defend their year-round stable home ranges that vary between 4 and 10 ha. ...

The Social Life of Owl Monkeys
  • Citing Chapter
  • September 2023

... We did not use time since last birth, as in the other two sets of analyses, because births, being highly seasonal, would have been correlated with the outcome variable. Second, we constructed 15 candidate models for which the outcome variable was whether dispersal occurred during the dry 'winter season', when resource abundance and temperatures are lowest [69]. The 'dry season' of May-August is a period of limited food availability [59]; groups occupy territories that provide reliable dry season foods within the core areas [58]. ...

What Owl Monkeys (Aotus spp.) Tell Us About the Dynamics Between Thermo-Energetics and Organismal Biology

... behavioural reproductive suppression). Specifically, adults may mate guard their partner, or act aggressively towards subadults, to prevent them from mating with the new unrelated individual [73,74]. It is also possible that a new adult entering the 13 group may not perceive the subadult as a high-quality mating partner and prefer to mate with the resident adult over the subadult. ...

Dispersal: A Critical Life History Stage Influencing Populations, Social Dynamics, and Individual Fitness
  • Citing Chapter
  • September 2023

... The animals were resting and covering themselves with a mixed structure of sticks, leaves, and leaf litter on the ground, a type of structure already documented in trees but different from the usual holes or cavities in trees (Aquino & Encarnación 1986;Case 2013;Helenbrook et al., 2019). Throughout our observations, we identified the male climbing in and out of the trees and returning to the sleeping sites (possibly by the researcher's presence); however, the female remained in the refuge, a possible territorial display like other neotropical primates (Rutberg 1983;Janson, 1986;Spence-Aizenberg et al. 2023; Figure 1; video in Supplementary material, Arango-Lozano 2024). We conducted a total of nine separate excursions, excluding the initial encounter on April 4th when we set up camera traps to monitor the activity of the individuals at the sleeping site. ...

Communication in Owl Monkeys
  • Citing Chapter
  • September 2023