Alouatta Research Articles

Landscape structure influences the eukaryome of a folivorous-frugivorous primate

ABSTRACT Eukaryotes are important components of primate gut communities. Despite their role in the diversity and structure of the gut ecosystem, microbiome research has focused on the prokaryotic component of the gut community. While gut bacteria are shaped by host phylogeny and diet, these factors are known to have negligible effects on eukaryotic diversity, which is expected to be modulated by the characteristics of the habitat. We assess the influence of landscape composition and configuration on the eukaryome of black and gold howler monkeys (Alouatta caraya). We collected fecal samples from 10 independent social groups inhabiting small forest fragments or orchards enriched with native tree species and applied an 18S rRNA gene fragment metabarcoding approach to describe their eukaryotic communities. We used generalized linear models to assess the power of landscape metrics in predicting the richness, diversity, evenness, and phylogenetic diversity of the eukaryome. Most communities were dominated by Ascomycota, and it is likely that many of the reads had an environmental origin. Forest cover affected eukaryome richness positively and patch density showed a positive relationship with the Simpson’s diversity and Pielou’s evenness indexes. Howler monkeys living in landscapes with lower habitat coverage had a lower eukaryotic alpha-diversity in the fecal microbiome.

Urinary health indicators in folivorous-frugivorous primates with and without food supplementation.

Food supplementation by humans in peri-urban and urban landscapes can lead to excessive intake of energy and certain macronutrients, and affect animal health. In this study, we evaluated the influence of food supplementation on urinary health indicators in brown howler monkeys (Alouatta guariba) by comparing supplemented and non-supplemented free-ranging peri-urban groups. We also evaluated the effect of sex, day shift, and season of sampling. Between August 2021 and August 2022, we non-invasively collected 61 samples (43 from females and 18 from males) from adult individuals (N = 10) in three supplemented groups and 56 samples (25 from females and 31 from males) from adults (N = 7) in three non-supplemented groups. The supplements, mostly raw foods (e.g., fruits, vegetables, and tubers) and bread, represented 18% of the total fresh mass ingested by the supplemented groups. We assessed pH, density, and the presence of eight urine components (glucose, bilirubin, ketones, protein, urobilinogen, nitrite, blood, and leukocytes) using reagent urine strips. Season of sampling predicted urine density (mean = 1.022), while both season and day shift predicted pH (mean = 6.5). The occurrence of supplementation was a weak predictor of these parameters. Finally, we detected leukocytes in 21% of the 117 samples. We did not identify any visible signs of disease in any individual throughout the study and found no clinical changes in urine under the conditions studied. We urge validation of the results with urine strips to facilitate monitoring of the health of howler monkeys living in anthropogenic landscapes in the presence or absence of dietary supplementation.

Detection of Filariid Infections in Mexican Primate Populations Through qPCR.

Filariae are parasitic nematodes of high veterinary and medical importance, responsible for some acute tropical diseases. They are transmitted through the bite of hematophagous vectors such as biting midges and blackflies. Filariae are among the most prevalent vector-borne parasitoses in Neotropical primates in which severe infections can cause inflammatory reactions and tissue damage. Given the location inside the host (peritoneal cavity, bloodstream, and lymphatics), the detection of filariid nematodes is challenging and is mostly postmortem; hence the scarcity of studies on the prevalence of filariae in wild primate populations. Here, we report the prevalence of filariid infections in free-ranging populations of Geoffroy's spider (Ateles geoffroyi) and black howler (Alouatta pigra) monkeys across southern Mexico, using a combination of noninvasive sampling and molecular diagnostic techniques. Fecal samples were screened for filariid DNA by qPCR protocols. A total of 88 samples were examined with an overall prevalence of 26%. Filariae were slightly more common in spider monkeys compared to howler monkeys. This study constitutes the first report of the prevalence of infection of filariid nematodes in populations of wild spider monkey across southern Mexico, and the first reporting of filariae in black howler monkeys, as part of a new era of primate parasitology and the diagnostics of parasite infections in light of the everyday more affordable molecular tools.

Mantled howler monkeys (Alouatta palliata) alter activity and spatial cohesion across a continuous forest and forest fragment in Costa Rica.

Habitat loss due to deforestation is a primary threat to global biodiversity. Clearing tropical rainforests for agriculture or development leads to forest fragmentation. Forest fragments contain fewer large trees and provide lower food availability for primates compared to continuous forests. Mantled howler monkeys (Alouatta palliata) inhabit fragmented rainforests and may need to alter their activity budgets and spatial cohesion to mitigate competition and conserve energy in fragments where food quality is lower. We compared howler monkey activity and spatial cohesion across a small forest fragment (La Suerte Biological Research Station, LSBRS) and a large, continuous forest (La Selva Research Station) in Costa Rica. We predicted that monkeys at LSBRS would rest more, feed more, travel less, and be less spatially cohesive compared to La Selva to contend with fewer resources in the small fragment. Using instantaneous scan sampling at 2-min intervals during 30-min focal samples, we recorded activity and the number of individuals within 5m of the focal animal. We collected 1505h of data from 2017-2024. Monkey activity and spatial cohesion differed significantly across sites. As predicted, monkeys at LSBRS spent more time feeding than at La Selva, but contrary to our predictions, they rested less and traveled more. The mean number of individuals within 5m was significantly lower at LSBRS compared to La Selva. The ability to modify their activity and spatial cohesion in response to fragmentation provides insight into how primates can contend with fewer resources and higher competition in changing ecosystems worldwide.

Howler Monkey Die-Off in Southern Mexico.

In May and June 2024, a die-off of Mexican mantled howler monkeys (Alouatta palliata mexicana) occurred in southern Mexico. This commentary documents the event, attributing it to extreme heatwaves, drought, wildfires, and habitat impoverishment. Despite their reported resilience to habitat disturbances, mantled howler monkey mortality rate in some areas reached 31%. Key evidence points to heatstroke as the primary cause of death, exacerbated by limited hydration and reduced dietary diversity in disturbed habitats. Immediate responses included community-led rescues (e.g., hydrating the monkeys), coordination of rescue activities by nongovernmental organizations (NGOs) (e.g., managing donations), involvement of scientists (e.g., monitoring of primate populations), and assistance from government officials (e.g., providing legal support for animal management). This event underscores the urgency of developing action plans to prevent and attend future crises. Among other actions, we highlight (i) establishing primate care infrastructure with medical and rehabilitation centers; (ii) developing protocols and training programs to ensure rapid crisis response; (iii) fostering collaboration among government, NGOs, and academic institutions for effective crisis management; and (iv) developing targeted research on climate change impacts, predictive models, and long-term health monitoring. We emphasize the critical need for coordinated conservation efforts to protect wild primates and maintain natural ecosystem resilience in the face of escalating climate challenges.

IMMOBILIZATION OF BLACK HOWLER MONKEYS (ALOUATTA PIGRA) USING BUTORPHANOL, AZAPERONE, MEDETOMIDINE IS SAFE AND EFFECTIVE FOR NONINVASIVE PROCEDURES.

Administration of butorphanol, azaperone, and medetomidine (BAM) for immobilization of black howler monkeys (Alouatta pigra) has not been previously reported. In this observational study, 0.02 ml/kg of compounded BAM (butorphanol 27.3 mg/ml, azaperone 9.1 mg/ml, medetomidine 10.9 mg/ml) was administered IM in 10 captive black howler monkeys. Time to immobilization was recorded, an arterial blood gas performed, and at 5-min intervals, HR, RR, oscillometric arterial blood pressure, SPO2, and rectal temperature were measured. Naltrexone and atipamezole were administered IM at procedure completion and recovery times were recorded. If invasive procedures such as surgery were necessary and additional drugs needed, further data from that individual was removed from data analysis. Final BAM dosages were 0.55 ± 0.12 mg/kg butorphanol, 0.19 ± 0.04 mg/kg azaperone, and 0.22 ± 0.05 mg/kg medetomidine. Nine of 10 monkeys achieved sedation allowing for physical exam, venipuncture, and tuberculin skin testing within 4 ± 2 min. No monkeys reached a plane of immobilization allowing for intubation. Physiologic variables were acceptable for this species. Hypoxemia (SPO2 < 95%) was observed in three monkeys via pulse oximetry, and normoxemia was observed on arterial blood gas. Recovery was smooth and rapid. Therefore, BAM is a viable option for noninvasive procedures or as a premedication prior to induction of anesthesia in black howler monkeys.

Bot fly parasitism in mantled howler monkeys (Alouatta palliata): General patterns and climate influences.

Parasitism is a strong selective pressure, and its study is crucial for predicting the persistence of host species. Mantled howler monkeys are infected by the larvae of the bot fly Cuterebra baeri. This parasitosis produces myiasis and may have negative impacts on host health, although systematic information on the dynamics of this host-parasite relationship is very limited. Currently, all available information on infection patterns of C. baeri comes from a single mantled howler monkey population (Barro Colorado Island, Panama). Therefore, in this study we describe temporal variation in infection patterns for a newly mantled howler monkey population and analyze the relationship between climate and infection likelihood. We assessed the presence of C. baeri nodules in 17 adult individuals in Los Tuxtlas for 10 months through direct observation and compiled data on ambient temperature and rainfall. Most subjects had nodules during the study and there were no differences between sexes in the number of nodules. Nodules were usually located in the neck. Prevalence and abundance of nodules peaked thrice during the study (February, April, and September), a pattern that was very similar to that of parasitism intensity (February, April, and August). Incidence closely tracked these peaks, increasing before and decreasing after them. The likelihood of nodule appearance increased when both mean and minimum temperature decreased in the 24-21 prior days to nodule appearance. It also increased with decreased rainfall in the 5-2 prior days to nodule appearance. Although only three of the eight analyzed climate variables had a significant effect on parasitosis, these results suggest that climate may affect pupal development and the access of larvae to hosts. Besides contributing data on C. baeri parasitism for a new mantled howler monkey population, our study provides novel information on the influence of environmental factors on the dynamics of host-parasite systems.

Acoustic recognition of predators by mantled howler monkeys (Alouatta palliata): A playback experiment with naïve and experienced subjects.

When the production of antipredator behaviors is costly, prey is expected to stop displaying such behaviors and lose the ability to recognize extirpated predators. However, the loss or maintenance of predator recognition abilities is conditional on the eco-evolutionary context of prey. Here, we examined the behavioral responses of naïve and experienced mantled howler monkeys (Alouatta palliata) to simulated acoustic cues from natural predators. We studied experienced individuals in the Uxpanapa Valley and naïve individuals in Los Tuxtlas (Veracruz, México). Jaguars (Panthera onca) and harpy eagles (Harpia harpyja), the main predators of howler monkeys, are extant in the Uxpanapa Valley but have been extirpated in Los Tuxtlas for approximately 70 and 45 years, respectively. We exposed six naïve and six experienced groups to playbacks of acoustic stimuli from the two predators and a non-predator control species (plain chachalacas, Ortalis vetula), and recorded the latency, frequency, and duration of antipredation behaviors (n = 127 trials). In contrast with experienced mantled howler monkeys, naïve subjects did not respond to trials from harpy eagles. However, response patterns were generally similar between naïve and experienced individuals when exposed to jaguar stimuli. Our findings suggest that naïve mantled howler monkeys do not recognize harpy eagle calls, but they respond to jaguar calls in a manner consistent with experienced individuals. These results illustrate how different mechanisms for the recognition of extirpated predators operate within a single species according to evolutionary and ecological experience.

Growth and allometric curves of southern brown howler monkey (Alouatta guariba): Insights on its ontogeny and conservation.

Ontogenetic sexual dimorphism is observed in different primate species, with ecological and evolutionary relationships explaining this pattern. Understanding the growth of the southern brown howler monkey elucidates not only the ecology and evolution but also contributes to conservation projects for this species. Throughout 20 years of the Centro de Pesquisas Biológicas de Indaial-Projeto Bugio, Brazil, we collected morphological data on 105 howlers of the Alouatta guariba species to identify the growth differences between ontogenetic categories and sexes and generate a growth curve to estimate the age of rescued individuals. Linear measurements were employed to obtain body length as well as the dimensions of the head and limbs. All individuals were also weighed to obtain body mass. We assessed growth rate and duration using allometric analysis based on the individuals' ages. We compared growth rate and duration among infant, juvenile, and adult howlers and between sexes. We provide growth curves for body size for both sexes using the Von Bertalanffy model. Infants have accelerated growth rate in comparison to the juveniles and adults, with no differences between sexes in establishing body length at this ontogenetic stage. Males have a prolonged development duration from the juvenile stage, reaching adulthood later than females, which explains the body length differences found in this species. Variables of head and limbs analyzed also showed differences in growth rate and duration, but not so consistently among ontogenetic stages. Mass was not a good variable to understand the growth differences of the animals, since many arrived feeble in the project and may have lost mass due to different circumstances in old age. Therefore, growth curves were obtained only for body length, allowing the estimation of the age of these animals when rescued from the wild to more effectively provide needed care in captivity.

Epidemiological characterization of oral focal epithelial hyperplasia in brown howler monkeys (Alouatta guariba clamitans).

Oral focal epithelial hyperplasia (FEH) is an uncommon infection affecting humans, chimpanzees, bonobos, and howler monkeys. This study describes 10 cases of free-ranging brown howler monkeys (Alouatta guariba clamitans) diagnosed with FEH and Alouatta guariba Papillomavirus 1 (AgPV 1). We analyzed demographic characteristics, rescue conditions, clinical and pathological findings, and species-specific behavior factors in these cases. The study assessed the frequency of occurrence and potential contributing factors of FEH and AgPV 1 infection. The frequency of FEH was 8.13%. Most affected howlers were adult or geriatric males with comorbidities or stressful conditions. Clinical and pathological observations were consistent with AgPV 1 infection. Species-specific behaviors and environmental stressors were identified as contributing factors. FEH associated with AgPV 1 affected mainly adult or geriatric males with ongoing comorbidities or stressful conditions. Further research is needed to understand these factors for effective management.

Temporal variation and age influence activity budget more than sex and reproductive status in wild brown howler monkeys (Alouatta guariba clamitans) inhabiting a large, continuous forest.

Activity budget analyses are important for understanding how animals spend their time in daily activities like resting, foraging, moving and socializing. These behaviors are closely linked to energy management, so habitat quality and resource availability are known to influence the activity budgets of species. Therefore, many studies have examined the consequences of habitat loss and fragmentation on the energetic demands and activity budgets of species. However, we still have limited knowledge of how animals behave in large, continuous, and protected environments, as such habitats are currently rare. The present study analyzed how temporal variation, age, sex and reproductive status influenced the activity budget of wild red howler monkeys (Alouatta guariba clamitans), in one of the last Atlantic Forest remnants that remains large and protected. Between November 2017 and December 2018, we monitored two groups, G3 and G4, in Parque Estadual Carlos Botelho, São Paulo, Brazil. The groups were composed of one adult male, two adult females and their offspring and one (G3) or two (G4) subadult males, using scan sampling for behavioral for data collection every 20min. The most common behavior was resting, followed by foraging, moving and social interactions, with inter-group differences. Temporal variation explained most of the fluctuations in the activity budget, so did age and sex, but to a lesser degree. The reproductive status of females did not alter their activity budget. These findings reveal that even neighboring groups display distinct and intricate relationships with their habitat. Future studies should be conducted in continuous forests to determine what is the expected range of variation in activity budget, particularly in those species considered as flexible and inhabiting endangered habitats, such as the Atlantic Forest.

Lingual neoplasia in nonhuman primates: Description of five cases and a literature review.

Documentation of lingual tumors is scarce in nonhuman primates. Through a multi-institutional retrospective study we compile cases of primary and metastatic neoplasia in non-human primates. We describe five cases of lingual neoplasia. Three cases are primary lingual tumors: chondro-osteoblastic lipoma in a howler monkey, squamous cell carcinoma, and fibroma in two baboons. We describe two cases of metastatic lymphoma in the tongue in rhesus macaques. A literature review of published lingual neoplasia in nonhuman primates is included in this manuscript. Lingual neoplasia is seldom reported in non-human primates.

Hematology and serum biochemistry of free-ranging mantled howler monkeys (Alouatta palliata) at La Pacifica, Costa Rica.

Hematologic and blood biochemical values are key tools for assessing primate health. A long-term behavioral study of howler monkeys at a single site (La Pacífica, Guanacaste, Costa Rica), afforded the opportunity to develop baseline values for a large group of animals, evaluating differences between adult males and females and comparing to a report in the same population two decades later. In 1998, 64 free-ranging mantled howler monkeys were anesthetized and sampled for hematologic and biochemical analysis. Blood analysis is reported for 29 adult females, 9 juvenile females, 19 adult males and 3 juvenile males. Four adults were excluded due to external injury or disease. There were few significant differences between adult females, juvenile females, and adult males. Baseline blood parameters are useful for determining normal values for howler monkey populations. The values for total protein, blood urea nitrogen, glucose, liver enzymes and potassium differed from a later study in 2019 may indicate changes that are influencing howler monkey health.

Mantled howler monkeys (Alouatta palliata) show no preferential hand use in two self-directed behaviors.

Hand preference is the preferential use of one hand for a single task. Its study provides insight into the neural mechanisms underlying motor skills, perception, and cognitive functions. From a comparative perspective, it also offers a window into evolutionary history, shedding light on whether manual preferences stem from genetics, environmental influences, or a combination of both. However, there is a paucity of information on preferential hand use for several primate taxa. Here we examine hand preference for the first time in mantled howler monkeys (Alouatta palliata) to determine if there is preferential hand use at the individual and population level as well as sex differences in hand use. We followed 17 wild adult individuals for 10months and used focal animal sampling (506 focal samples) to record hand use in two types of self-directed behaviors, touching (1246 events) and scratching (1115 events). According to the binomial tests, four individuals were right-hand-preferent, two were left-hand-preferent, and 11 were ambilateral during touching, whereas for scratching seven individuals were right-hand-preferent, two were left-hand-preferent, and eight were ambilateral. At the population level, there was ambilaterality in both behaviors. At the individual level, according to the HI index, hand preference in touching and scratching were not associated and did not vary between sexes. These findings concur with previous studies with howler monkeys and other taxa suggesting that population-level hand preference is not a universal trait across primates.

FIELD TECHNIQUES FOR VASECTOMY IN BLACK HOWLER MONKEYS (ALOUATTA PIGRA).

Three adult black howler monkeys (Alouatta pigra) were vasectomized for the purpose of population control. Two different surgical approaches (inguinal and pelvic) were used to vasectomize the animals under general anesthesia. One monkey was vasectomized with a pelvic approach, and the other two monkeys were vasectomized with an inguinal approach. The inguinal approach was minimally invasive and proved to be an effective field procedure, utilizing minimal surgical equipment with a mean operative time of 35 min. The inguinal approach allowed for better visualization of the spermatic cord, which prompted easier ligation and transection of the ductus deferens. Identification of the ductus deferens was successfully performed intraoperatively using a tuberculin syringe to aseptically aspirate cord contents, as histopathology was not available. All howler monkeys fully recovered without complication. The social hierarchy of the troop and mating behavior has not been affected. There have been no new pregnancies reported in the troop since the vasectomies were performed. The inguinal approach is preferred as it is minimally invasive and can be performed confidently in a field setting.

Teenagers' perceptions of Mexican primates: A participatory environmental education program for the conservation of mantled howler monkeys (Alouatta palliata) in Los Tuxtlas, Mexico.

This study explores the perceptions that high school students have about mantled howler monkeys in the Mexican community of Balzapote, Veracruz. We systematized the learning process derived from a Primate Conservation Education Program (PCEP) based on participatory action research (PAR) and arts-based education. Our results indicate a decrease in students' fear of monkeys, the recovery of myths and legends about this species, as well as a complex knowledge about monkeys and their habitat. The inclusion of local knowledge enriched the learning experience and reinforced primate conservation concepts. The PAR and arts-based approaches allowed students to internalize and apply acquired knowledge and fostered empathy. In addition to learning, the approach helped develop teamwork, critical thinking, and creative skills. Quantitative indicators showed shifts in emotions and knowledge post-program, and qualitative data revealed a deep articulation of learned content. We also identified migration and mining activities as socio-political factors impacting local people's livelihoods and wildlife conservation in this region.

Leadership and the finder's advantage in mantled howler monkeys.

Leading collective movements and arriving first at feeding sites may improve food acquisition. Specifically, the first individual to discover and exploit a feeding site may gain a feeding advantage known as the "finder's advantage."The aim of this research was to verify if the probability of leading group movements to feeding sites in mantled howler monkeys (Alouatta palliata) varied by sex and reproductive status, and whether finders had higher foraging success than followers. We studied 18 adult individuals from two groups in La Flor de Catemacoover a year (978 h), and sampled group movements (n = 211) and foraging behavior (n = 215 feeding episodes). Gestating females were leaders and finders of group movements to feeding sites more often than expected but were also replaced in the leading position more frequently than individuals of other sex/reproductive states. Feeding behavior was not influenced by the order of arrival at feeding sites per se, but gestating females had higher food intake rate, bite rate, and feeding time when arriving earlier (i.e., occupying front group positions) than later. Therefore, leadership and the finder's advantage occur in this species and are probably employed by gestating females to maintain their energetic condition.

Facial and ocular thermal mapping in black-and-gold howler monkey (Alouatta caraya) by infrared thermography: An ex situ study.

This study used infrared thermography (IRT) for mapping the facial and ocular temperatures of howler monkeys, to determine parameters for the diagnosis of febrile processes. There are no published IRT study in this species. Were evaluated images of a group of monkeys kept under human care at Sorocaba Zoo (São Paulo, Brazil). The images were recorded during 1 year, in all seasons. Face and eye temperatures were evaluated. There are statistically significant differences in face and eye temperatures. Mean values and standard deviations for facial and ocular temperature were respectively: 33.0°C (2.1) and 36.5°C (1.9) in the summer; 31.5°C (4.5) and 35.3°C (3.6) in the autumn; 30.0°C (4.3) and 35.6°C (3.9) in the winter; 30.8°C (2.9) and 35.5°C (2.1) in the spring. The IRT was effective to establish a parameter for facial and ocular temperatures of black-and-gold howler monkeys kept under human care.

Cryopreservation of spermatozoa from black-and-gold howler monkeys (Alouatta caraya) using egg yolk-based or soy lecithin-based extenders.

There are more than 200 species and subspecies of Neotropical Primates of which more than 40% are listed as threatened by the IUCN Red List of Threatened Species. Both in situ and ex situ conservation programs can benefit from the use of assisted reproductive technologies. The objective of this study was to evaluate, for the first time, cryopreservation techniques for Alouatta caraya semen. Semen samples were collected from five adult males, analyzed, and frozen in either Test-egg yolk or Test-soy lecithin-based extenders containing either 3 or 4% glycerol. Frozen-thawed samples were analyzed at 10, 40, and 80min post-thaw. Egg yolk-based extenders were overall better than soy lecithin-based extenders. There was no significant difference between 3 and 4% glycerol in any of the parameters analyzed, however, 4% glycerol in egg yolk-based extender produced more favorable results for total motility, intact plasma membrane, lipidperoxidation, and DNA fragmentation index. This study brought novel information on semen characteristics and cryopreservation aspects for A. caraya, which can help shape future experiments to improve the outcome of frozen-thawed sperm for this and other species of Neotropical primates.

Restoration of Alouatta guariba populations: building a binational management strategy for the conservation of the endangered brown howler monkey of the Atlantic Forest

The brown howler monkey (Alouatta guariba) is endemic to the Atlantic Forest of eastern Brazil and northeastern Argentina, threatened by extinction due to habitat loss and fragmentation, and hunting. Its reduced and isolated populations dramatically decreased and suffered local extinctions after recent yellow fever outbreaks, recommending the species risk uplist from Vulnerable to Endangered. In Brazil, the species occurs along eight states in sparse populations, including some large protected areas, and is being uplisted to Endangered. Following the National Action Plan for Conservation of the Atlantic Forest Primates and the Maned-sloth, and applying the Guidelines for Reintroductions and other Conservation Translocations (IUCN/CTSG), the Ex Situ Guidelines (IUCN/CPSG) and the One Plan Approach (IUCN/CPSG), a workshop was held on August 2021 to evaluate the need, requisites and roles of an integrated Population Management Program for A. guariba. Such program was developed in June 2022 defining the objectives of (i) restore in situ populations from ex situ populations, prioritizing populations in higher risk to prevent local extinctions, and (ii) establish an ex situ insurance population. This in situ – ex situ integrated management program was approved by ICMBio in February 2023, with actions recommended for all states along the species distribution. In Argentina, the species is Critically Endangered, with a remaining population of 20-50 individuals. Following the National Plan for Primate Conservation in Argentina, in a process similar to that in Brazil, two workshops were held in 2022/2023 to evaluate and define management actions for the long-term recovery of A. guariba. The priorities indicated were (i) reintroduction in ten potential areas in Misiones – due to a lower risk when compared to reinforcement of remaining populations, and (ii) establishing an ex situ management program in Argentina – still non-existent. The progressive collaboration between the initiatives of both countries is promoting the exchange of experiences and the integration of strategies. Here we summarize the planning and management carried out in Brazil and Argentina, highlighting the need for integrated measures. We debate on the progress and challenges, proposing next steps for developing and implementing a binational population management program for the conservation of the brown howler monkey.