Size, Site Fidelity, and Overlap of Home Ranges and Core Areas in the Socially Monogamous Owl Monkey (Aotus azarae) of Northern Argentina

Intergroup encounters in pair-living primates: Comparative analysis and a case study of pair-living and monogamous owl monkeys (Aotus azarae) of Argentina

The function of intergroup encounters (IGEs) may differ substantially among species of different group sizes and social organizations. Research in group-living primates has shown that the behavioral responses during IGEs can vary widely from affiliative to neutral or aggressive interactions; still, little is known about IGEs in pair-living taxa. We conducted a systematic literature review to find relevant studies on the functions of IGEs in pair-living nonhuman primates that could inform analyses of IGE data (n = 242 IGEs, 21 groups and 10 solitary individuals, 1997-2020) from wild owl monkeys, a pair-living, monogamous primate with extensive biparental care. We identified 1315 studies published between 1965 and 2021; only 13 of them (n = 10 species) contained raw data on the number of IGEs. Our review of those studies showed that IGEs are common, but highly variable in their nature and characteristics in pair-living primates. To examine the non-mutually exclusive hypotheses of resource-, and mate defense, and infanticide avoidance we analyzed data from the Owl Monkey Project 27-year long database to build first an a priori model set. To incorporate prior knowledge from the literature review, we conducted our analyses as a consecutive series of binomial logistic regressions. All IGEs including all biologically relevant parameters (N = 156) were codified into three different behavioral categories (Reaction, Agonism, and Physical Aggression). The analysis showed that owl monkeys regularly engaged in IGEs, most of which were agonistic. They showed more reaction when infants were present, but reactions were less physically aggressive when infants and pregnant females were involved. Overall, our results lend more support for the infant and mate defense hypotheses than they do for the resource defense one.

Seasonal range fidelity of a megaherbivore in response to environmental change

For large herbivores living in highly dynamic environments, maintaining range fidelity has the potential to facilitate the exploitation of predictable resources while minimising energy expenditure. We evaluate this expectation by examining how the seasonal range fidelity of African elephants (Loxodonta africana) in the Kruger National Park, South Africa is affected by spatiotemporal variation in environmental conditions (vegetation quality, temperature, rainfall, and fire). Eight-years of GPS collar data were used to analyse the similarity in seasonal utilisation distributions for thirteen family groups. Elephants exhibited remarkable consistency in their seasonal range fidelity across the study with rainfall emerging as a key driver of space-use. Within years, high range fidelity from summer to autumn and from autumn to winter was driven by increased rainfall and the retention of high-quality vegetation. Across years, sequential autumn seasons demonstrated the lowest levels of range fidelity due to inter-annual variability in the wet to dry season transition, resulting in unpredictable resource availability. Understanding seasonal space use is important for determining the effects of future variability in environmental conditions on elephant populations, particularly when it comes to management interventions. Indeed, over the coming decades climate change is predicted to drive greater variability in rainfall and elevated temperatures in African savanna ecosystems. The impacts of climate change also present particular challenges for elephants living in fragmented or human-transformed habitats where the opportunity for seasonal range shifts are greatly constrained.

Prioritizing Areas for Primate Conservation in Argentina

Argentina lies within the southernmost distributional range of five neotropical primates, the brown howler monkey Alouatta guariba, the black-and-gold howler monkey Alouatta caraya, the black-horned capuchin Sapajus nigritus, the Azara’s capuchin Sapajus cay, and the Azara’s owl monkey Aotus azarae; the first three of which are globally threatened. These species occupy different ecoregions: the Alto Paraná Atlantic forest, the Araucaria moist forest, the humid Chaco, the Southern Cone Mesopotamian savanna, the Paraná Ffooded savanna, and the Southern Andean Yungas. The recently approved National Primate Conservation Plan of Argentina calls for identifying priority areas to focus conservation actions for these species. We used species distribution models to estimate species ranges and then used the Zonation software to perform a spatial conservation prioritization analysis based on primate habitat quality and connectivity to identify potential areas of importance at national and ecoregional levels. Only 7.2% (19,500 km2) of the area inhabited by primates in Argentina is under protection. Outside the current protected areas, the top-ranked 1% and 5% priority areas identified in our analysis covered 1894 and 7574 km2, respectively. The top 1% areas were in the Atlantic forest of Misiones province, where S. nigritus, A. guariba, and A. caraya are distributed, and in the humid portion of eastern Chaco and Formosa provinces, where A. azarae and A. caraya are present. The top 5% areas included portions of the Yungas, where S. cay is the only primate present. Priority areas in Chaco and Formosa provinces are particularly relevant because of the paucity of protected areas and the high deforestation rate. The endangered A. guariba population will benefit from the better protection of the priority areas of Misiones. The potential priority areas proposed herein, considered within a context of a broad participatory process involving relevant stakeholders and local people, will help guide new and innovative conservation policies and practices while supporting management objectives.

Ranging behavior and the potential for territoriality in pair-living titi monkeys (Plecturocebus discolor)

Patterns of ranging behavior and space use are key for evaluating current ideas about the evolution and maintenance of pair-living and sexual monogamy as they provide insights into the dispersion of females, the potential for territoriality, and whether males are limited to defending an area that can support only one female and her offspring. We examined ranging behavior and space use to evaluate the potential for territoriality in five groups of red titi monkeys (Plecturocebus discolor) during a 10-year study in Ecuadorian Amazonia. Mean home range size, calculated using a time-sensitive local convex hull estimation procedure, was 4.0 ± 1.4 ha. Annual home ranges of neighboring groups overlapped, on average, 0%-7%. Mean daily path length was 670 ± 194 m, resulting in defendability indices of 2.2-3.6 across groups. Groups visited, on average, 4 of 12 sections of their home range border area per day, but that was not more often than would be expected by chance, and intergroup encounters were infrequent. We did not find evidence of active monitoring for intruders in border areas, in that groups did not travel either faster or slower when at the border than when in central areas of their range. The absence of overt monitoring might be compensated for by engaging in loud calls, which the study groups did throughout their home ranges; these calls may serve as an advertisement of occupancy and a deterrent to intruding conspecifics. Our finding that red titis have a high potential for territoriality is consistent with several of the main hypotheses proposed to explain pair-living in mammals.

The evolution of pair-living, sexual monogamy, and cooperative infant care: Insights from research on wild owl monkeys, titis, sakis, and tamarins

"Monogamy" and pair bonding have long been of interest to anthropologists and primatologists. Their study contributes to our knowledge of human evolutionary biology and social evolution without the cultural trappings associated with studying human societies directly. Here, we first provide an overview of theoretical considerations, followed by an evaluation of recent comparative studies of the evolution of "social monogamy"; we are left with serious doubts about the conclusions of these studies that stem from the often poor quality of the data used and an overreliance on secondary sources without vetting the data therein. We then describe our field research program on four "monogamous" platyrrhines (owl monkeys, titis, sakis, and tamarins), evaluate how well our data support various hypotheses proposed to explain "monogamy," and compare our data to those reported on the same genera in comparative studies. Overall, we found a distressing lack of agreement between the data used in comparative studies and data from the literature for the taxa that we work with. In the final section, we propose areas of research that deserve more attention. We stress the need for more high-quality natural history data, and we urge researchers to be cautious about the uncritical use of variables of uncertain internal validity. Overall, it is imperative that biological anthropologists establish and follow clear criteria for comparing and combining results from published studies and that researchers, reviewers, and editors alike comply with these standards to improve the transparency, reproducibility, and interpretability of causal inferences made in comparative studies.

Northern pigtailed macaques rely on old growth plantations to offset low fruit availability in a degraded forest fragment

Space-use and foraging strategies are important facets to consider in regard to the ecology and conservation of primates. For this study, we documented movement, ranging, and foraging patterns of northern pigtailed macaques (Macaca leonina) for 14 months in a degraded habitat with old growth Acacia and Eucalyptus plantations at the Sakaerat Biosphere Reserve in northeastern Thailand. We used hidden Markov models and characteristic hull polygons to analyze these patterns in regard to fruit availability. Macaques' home range (HR) was 599 ha and spanned through a natural dry-evergreen forest (DEF), and plantation forest. Our results showed that active foraging increased with higher fruit availability in DEF. Macaques changed to a less continuous behavioral state during periods of lower fruit availability in DEF, repeatedly moving from foraging to transiting behavior, while extending their HR further into plantation forest and surrounding edge areas. Concomitantly, macaques shifted their diet from fleshy to dry fruit such as the introduced Acacia species. Our results showed that the diet and movement ecology adaptations of northern pigtailed macaques were largely dependent on availability of native fruits, and reflected a "high-cost, high-yield" foraging strategy when fresh food was scarce and dry fruit was available in plantation forest. Conversely, wild-feeding northern pigtailed macaque populations inhabiting pristine habitat approached a "low-cost, low-yield" foraging strategy. Our results outline the effects of habitat degradation on foraging strategies and show how a flexible species can cope with its nutritional requirements.

Sexual dimorphism in the loud calls of Azara's owl monkeys (Aotus azarae): evidence of sexual selection?

Primates use different types of vocalizations in a variety of contexts. Some of the most studied types have been the long distance or loud calls. These vocalizations have been associated with mate defense, mate attraction, and resource defense, and it is plausible that sexual selection has played an important role in their evolution. Focusing on identified individuals of known sex and age, we evaluated the sexual dimorphism in a type of loud calls (hoots) in a population of wild owl monkeys (Aotus azarae) in Argentina. We found evidence of sexual dimorphism in call structure, with females and males only emitting one type of call, each differing in dominant frequency and Shannon entropy. In addition, both age-related and sex-specific differences in call usage were also apparent in response to the removal of one group member. Future acoustic data will allow us to assess if there are individual characteristics and if the structure of hoot calls presents differences in relation to the social condition of owl monkeys or specific sex responses to variants of hoot calls' traits. This will provide deeper insights into the evolution of vocal mechanisms regulating pair bonding and mate choice strategies in this and other primate species.

Ranging behavior and potential for territoriality in equatorial sakis (Pithecia aequatorialis) in Amazonian Ecuador

OBJECTIVES

Territoriality refers to the consistent defense of an area within the home range (HR) against intrusions of conspecifics. It implies exclusive space use with low degree of overlap among neighboring groups, high site fidelity, specific ranging behavior such as high mobility relative to HR size and frequent visits of territory borders, and monitoring behavior. We examined ranging behavior and use of space to evaluate territoriality in Pithecia aequatorialis in Ecuador.

MATERIALS AND METHODS

Between 2005 and 2015, we monitored one main study group continuously and five additional groups for shorter periods (5 months to 2.5 years) at the Tiputini Biodiversity Station, in eastern Ecuador. We scored the location of the study groups at 20 min intervals during, on average, 5 days per month. We estimated saki HRs and core areas (CAs) using the fixed kernel density method (95 and 50%, respectively).

RESULTS

The average HR size was 57 ha and the average CA 14 ha. The degree of overlap between HRs of neighboring groups was low (2-9%). For the main study group, the average overlap between annual HRs was 82%. Mean daily path length across groups was 1,151 m; the defensibility index varied between 1.1 and 2.3 (values >1 are suggestive of territoriality), and the fractional monitoring rate varied between 0.06 and 0.15 (values >0.08 are suggestive of territoriality). Groups did not visit their HR borders (100 m inner buffer) more often than would be expected by chance. Travel speed and directness were comparable between the borders and the centers of groups' HRs.

DISCUSSION

Our multiyear study suggests that equatorial sakis show low degree of range overlap and high site fidelity and have the potential to be territorial, given their high mobility relative to HR size that allows for frequent border monitoring. Nevertheless, their movement patterns in border areas did not reveal evidence for monitoring behavior.

Characterization of the Tree Holes Used by Lepilemur ruficaudatus in the Dry, Deciduous Forest of Kirindy Mitea National Park

Knowledge of the key resources for a species is critical for developing an effective conservation strategy. Kirindy Mitea National Park is an important refuge for the red-tailed sportive lemur (Lepilemur ruficaudatus), a nocturnal folivorous lemur endemic to the dry deciduous forest of western Madagascar. Because L. ruficaudatus sleeps in tree holes during the day, sleeping trees may be an important resource for this species. Our goal was to characterize the sleeping sites used by L. ruficaudatus at the Ankoatsifaka Research Station in Kirindy Mitea National Park. In July and August 2012, tree characteristics were recorded for 60 L. ruficaudatus sleeping sites. Intact and alive trees, particularly Strychnos madagascariensis, were preferred by L. ruficaudatus. Sleeping holes were generally located in taller trees (median hole height = 4 m) and in trees with large girths (median = 20.5 cm). Greater protection from predators and thermal shifts may be provided by intact trees and concealed tree holes. Because tree characteristics can influence the presence and abundance of forest-living primates, the availability and characteristics of particular trees as potential sleeping shelters in a habitat must be taken into account in conservation strategies for L. ruficaudatus.

Age and sex-specific mortality of wild and captive populations of a monogamous pair-bonded primate (Aotus azarae)

In polygynous primates, a greater reproductive variance in males have been linked to their reduced life expectancy relative to females. The mortality patterns of monogamous pair-bonded primates, however, are less clear. We analyzed the sex differences in mortality within wild (NMales  = 70, NFemales  = 73) and captive (NMales  = 25, NFemales  = 29) populations of Azara's owl monkeys (Aotus azarae), a socially and genetically monogamous primate exhibiting biparental care. We used Bayesian Survival Trajectory Analysis (BaSTA) to test age-dependent models of mortality. The wild and captive populations were best fit by the logistic and Gompertz models, respectively, implying greater heterogeneity in the wild environment likely due to harsher conditions. We found that age patterns of mortality were similar between the sexes in both populations. We calculated life expectancy and disparity, the latter a measure of the steepness of senescence, for both sexes in each population. Males and females had similar life expectancies in both populations; the wild population overall having a shorter life expectancy than the captive one. Furthermore, captive females had a reduced life disparity relative to captive males and to both sexes in the wild. We interpret this pattern in light of the hazards associated with reproduction. In captivity, where reproduction is intensely managed, the risks associated with gestation and birth are tempered so that there is a reduction in the likelihood of captive females dying prematurely, decreasing their overall life disparity.

Larger lizards live longer in the group-living Egernia stokesii

Animal space use has implications for gene flow, disease dynamics, mating systems and the evolution of sociality. Given recent attention to sociality in reptiles, lizards are an important group for expanding our understanding of animal space use. Lizard space use is commonly investigated within one population over a short period and limited attention has been given to potential predictors of site fidelity. This study evaluated site fidelity in three populations of group-living Egernia stokesii (gidgee skink) between two field surveys separated by almost a decade. Of 43 recaptured lizards, 28 (65%) occupied their original space, and 15 (36%) of those shared their space with the same other lizard or lizards in both surveys. This confirmed long-term site and social bond fidelity in E. stokesii. We found that larger lizards were more likely to be recaptured. Neither body size, individual genetic heterozygosity, nor the availability of refuges strongly predicted whether lizards were recaptured in the same or a different place. The reasons why some lizards stayed in the same space while others moved are yet to be resolved.