Patrícia Izar

The consumption of small vertebrates occurs to varying degrees among many non-human primates. This dietary element may have constituted an important source of nutrition for early hominins, particularly during periods of food scarcity, providing a stepping stone to the exploitation of larger animals. Capuchin monkeys regularly consume small vertebrates across their range. Expanding our knowledge of the contribution of animal matter to these primates’ diets can shed light on the proximate and ultimate drivers of small vertebrate consumption across primate taxa, including humans. We report on the most extensive record of bearded capuchin ( Sapajus libidinosus ) vertebrate predation so far available: 45 months of observations of vertebrate predation in two sympatric groups in Fazenda Boa Vista, in northeastern Brazil. We estimated the effect of provisioning, sex, age class, fruit and insect availability, rainfall, humidity, and temperature on predation rates using a zero-inflated negative binomial algorithm with random effects. We found mammal and saurian consumption is habitual in this population of S. libidinosus . Prey brains and viscera tend to be accessed before the rest of the body. Predation rates were higher in males compared to females and in adults compared to infants across groups. Our results also identified small vertebrates as key energy sources for bearded capuchins under decreased fruit availability and show that provisioning reduces predation rates. Future work should assess small vertebrate predation as a possible stepping stone in the emergence of human exploitation of large animals by re-analyzing fossil faunal assemblages for evidence of small vertebrate predation.

In primates, food sharing from mothers to infants may serve two main functions: supporting offspring nutritional needs (nutritional hypothesis) and facilitating the acquisition of dietary knowledge, such as what and how to eat (informational hypothesis). We investigated these hypotheses in a wild population of bearded capuchin monkeys Sapajus libidinosus , at Fazenda Boa Vista, Brazil. We analyzed 194 h of footage of 10 infants filmed over their first 18 months of life using focal animal sampling. Mothers shared food exclusively in response to infant solicitation, with solicitation events observed across 48 mother feeding episodes. Infants were successful in obtaining food in 29 bouts but failed in 19. In 15 of the 29 successful bouts, mothers only shared food after repeated solicitations, suggesting that food sharing involves a negotiated process. We found partial support for the nutritional hypothesis: food sharing increased as the infants aged. Infants also solicited more high‐quality and hard‐to‐process food items, but food sharing did not differ according to these food categories. Additionally, mothers were less likely to share lizards. Our findings suggest that food sharing in capuchins is driven primarily by infant begging, rather than active maternal investment, highlighting the dynamic interplay between mother and infant in promoting infant development.

Bimanual coordination is considered a crucial factor in the evolution of manual lateralization. Experimental tasks requiring the simultaneous and coordinated use of both hands induce hand preferences at the population level across various nonhuman primate species studied in captive environments. However, to date, research investigating laterality in bimanual coordination within natural settings remains scarce, especially with respect to platyrrhine taxa. We assessed hand preference in a bimanual coordinated extractive foraging task by wild bearded capuchin monkeys, Sapajus libidinosus , living in the Cerrado/Caatinga ecotone, Northeast Brazil. Nineteen individuals were filmed during the consumption of four different nut species for 4 months. A detailed video‐coding analysis was conducted on their hand movements to extract the edible kernel(s) from the nuts. Overall, most individuals were lateralized, and as a group, capuchins significantly preferred their right‐hand fingers for extracting the kernel, thus suggesting an advantage of the left hemisphere for fine finger movements. The comparison with captive capuchins previously tested with an experimental bimanual coordinated task (the tube task), revealed that the direction of the preference did not differ between wild and captive individuals, although the latter tended to use their preferred hand more consistently. Our findings are in line with a growing body of evidence suggesting that bimanual coordination might have played a major role in the evolution of limb preference for motor action in primates and indicate that the study of coordinated bimanual behaviors in natural settings provides a valuable contribution to the understanding of manual laterality.

When dispersed, some primates’ species can use long-range vocalizations to exchange information about spatial position within the group and to coordinate behaviors, and it is also believed that these vocalizations play a role in communication between groups. These vocalizations help adjust the distance between individuals and are individually recognized. Thus, our objective was to analyze whether the distance between individuals within the group changes after a long-range vocalization. The target of the study was the population of black capuchin monkeys (Sapajus nigritus cucullatus) inhabiting an area within the southeastern Brazilian Atlantic Forest, the Carlos Botelho State Park. We measured group spread: the distance between the coordinates of the location of the tree most distant group members at every 5 min during entire days. Long-range vocalizations were recorded as all occurrences. The transfer function, analysis derived from time series, indicated that the distance between individuals decreased in the first scan after each long-range vocalization. We conclude that long-range vocalizations can be considered as one of the mechanisms responsible for maintaining distance between individuals of the same group.

Primates exhibit the richest cultural repertoire among animal taxa, spanning foraging, communication, sociality and tool use. Understanding the cultural behaviours of primates has strongly influenced the study of animal behaviour and challenged traditional views that culture is exclusive to humans. With nearly 60% of primate species endangered owing to human-driven habitat changes, recent calls have emerged to integrate cultural diversity into conservation strategies. However, the integration of culture into primate conservation requires careful planning to avoid misallocation of resources or skewed conservation priorities. Our review reveals that studies on primate culture are limited to less than 3% of extant species, largely owing to taxonomic and methodological biases favouring long-term observations in protected habitats. We propose that including culture in conservation policies can broaden the scope of research, fostering more inclusive conservation agendas that address taxa with diverse habitats and underexplored cultural traits. Furthermore, anthropogenic habitat changes can both erode and foster cultural behaviours, emphasizing the need for context-specific conservation strategies. We suggest that recognizing cultural traits in conservation frameworks may enhance the resilience of primate populations in changing environments. This approach promises a more comprehensive and equitable allocation of conservation efforts, preserving both the biological and cultural diversity of primates. This article is part of the theme issue ‘Animal culture: conservation in a changing world’.

The evolutionary origins of caring for dead conspecifics are not completely understood. While nonhuman animals’ understanding of changes in the state of a dead conspecific is debated, some exhibit behaviors consistent with experiencing emotional distress. Among nonhuman primates, the most common behavioral patterns related to the death of a group member include carrying and taking care of the deceased individual. The behavioral responses of the mother and other conspecifics towards a dead infant can be quantified to explore the underlying mechanisms and the evolutionary roots of these behaviors. Here, we report and quantify a probable case of infanticide in a wild group of capuchin monkeys, Sapajus xanthosternos, followed by the carrying and caring of the corpse by a primiparous mother. In our observation, the female maintained contact with the dead infant for 90% of the observed time, allowing other group members to approach and inspect the dead body, although only adult females and youngsters showed interest. The carrying of the corpse despite locomotion challenges, grooming and protecting it, and the apparent gradual adjustment to its unresponsive state (evidenced by unconventional carrying) suggest a potential coping strategy for dealing with the lack of feedback from the deceased. This study contributes to the field of comparative thanatology by documenting post-mortem behaviors in a primate species for which no prior record exists, broadening our understanding of such responses beyond humans.

Objectives: A hallmark of hominin evolution is the advent and diversification of stone tool use, and biological anthropologists have a particular interest in characterizing tool use behaviors in different hominin species. Robust capuchins, the genus Sapajus, are an excellent convergent model system for understanding tool use evolution, principally in the context of foraging, in terms of how they use stones to process hard fruits. However, most published studies of capuchin tool use in the wild focus on the species Sapajus libidinosus. In order to strengthen comparative analyses, it is important to do research across robust capuchin species to understand tool use capacities and variation across the genus. The first indirect evidence that reported tool use in wild S. xanthosternos was in 2009, but since that time no additional publications have described this behavior for this species. In this study we provide the first complete characterization of tool use in wild S. xanthosternos for two areas within Montes Claros, Minas Gerais state, Brazil: Santa Rosa de Lima district, and Lapa Grande State Park. We compare our findings to the stone tool use characteristics reported in wild Sapajus libidinosus and other capuchin monkey species.Materials and Methods: In monthly surveys from January to September 2018, we walked trails through the two study areas and categorized tool use site characteristics, including anvil area, height, and perimeter; hammer stone weight; and species of fruit utilized. Additionally, we utilized camera traps at high‐use sites.Results: We describe the tools used by S. xanthosternos at 169 sites clustered in seven Nutcracking Areas, for processing three different species of encased fruit: Macaúba (Acrocomia aculeata), Cansaçao (Cnidoscolus pubescens), and Guariroba (Syagrus oleracea). With camera traps, we directly observed tool use behavior for the first time in this species.Discussion: Sapajus xanthosternos displayed tool use patterns very similar to those of S. libidinosus. The main difference was in regards to physical force; in our study, the mean weight of stones used by S. xanthosternos was higher than the mean reported for S. libidinosus at most field sites; however, there was no difference in hammer weight between S. libidinosus and S. xanthosternos when hammering Macaúba. We also registered the heaviest hammer stone for tool use (7.675 kg) known for the robust capuchin genus. It is clear from our study that tool use capacity and characteristics are conserved across the radiation of extant Sapajus, suggesting a possible stone tool use cognitive capacity spanning up to 3.3 million years of diversification within this genus. Unlike stone tool use occurring throughout the year for S. libidinosus, at our study sites S. xanthosternos used nutcracking tools only during the dry season.

Conservation funding is currently limited; cost‐effective conservation solutions are essential. We suggest that the thousands of field stations worldwide can play key roles at the frontline of biodiversity conservation and have high intrinsic value. We assessed field stations’ conservation return on investment and explored the impact of COVID‐19. We surveyed leaders of field stations across tropical regions that host primate research; 157 field stations in 56 countries responded. Respondents reported improved habitat quality and reduced hunting rates at over 80% of field stations and lower operational costs per km ² than protected areas, yet half of those surveyed have less funding now than in 2019. Spatial analyses support field station presence as reducing deforestation. These “earth observatories” provide a high return on investment; we advocate for increased support of field station programs and for governments to support their vital conservation efforts by investing accordingly.