ABSTRACTVariation in the expression of behavior is a critical measure for understanding how socio‐ecological factors shape cognitive and behavioral evolution and adaptability. Detailed descriptions of behavioral repertoires and how they are combined and structured into programs of actions is an essential foundation for this work. However, comparisons within and across species are made challenging where there is substantial variation in the level of detail at which behaviors are described. Here, we use a systematic, multi‐level framework to describe a recently reported chimpanzee tool use behavior—algae fishing—at three levels of granularity: Functional Behavioral Categories, Behaviors, and Behavioral Elements. We then describe how these units are combined into structured programs of action. Despite variation in the detail at which tool use behaviors are described in the literature, we suggest that chimpanzees' algae fishing repertoire is relatively large, as compared to other forms of chimpanzee tool using, and flexibly deployed at each level of description. The varied use of techniques by adults suggests that there is no single optimal solution for algae fishing, and that chimpanzees benefit from maintaining multiple strategies for this dynamic foraging challenge. We provide an example of a structured framework that can be applied to describe different levels of detail and used to show within‐ and between‐task variation. Systematic frameworks that can be consistently applied across species and contexts are critical for providing the like‐with‐like comparisons necessary for robust investigations of species‐level cognition and behavior.

ABSTRACTThe ongoing decline of non‐human primates places renewed emphasis on monitoring health in wild populations. Non‐invasive monitoring of reliable biomarkers of inflammation and immune activation allows researchers to assess individual health status without capturing or interfering with wild animals, but studies are limited by the availability of such biomarkers that are measurable from fecal and urine samples. In the present study, we aimed to validate the measurement of fecal haptoglobin, a biomarker primarily studied in relation to gut‐associated inflammation, in wild white‐faced capuchin monkeys (Cebus imitator), and to evaluate the relationship between fecal haptoglobin concentrations and age, sex, dominance rank, circadian effects and environmental factors including temperature and rainfall. We analytically validated the measurement of fecal haptoglobin in white‐faced capuchins. Our subsequent results did not demonstrate a relationship between haptoglobin concentrations and age, sex, dominance rank or circadian effects. However, we found significant influences of environmental conditions on fecal haptoglobin concentrations, with an increase and more variation observed during drier conditions in the early dry season, when the animals are typically under greater environmental stress. We conclude that haptoglobin measurement is feasible in wild white‐faced capuchin monkeys, and its concentrations vary in our study population, reflecting seasonal patterns of inflammation that are consistent with changes to environmental stressors associated with lower access to food and water.

In primate species, females communicate their reproductive status through multiple sensory channels, with visual signals such as swelling size being well documented. We investigated whether thermal (swelling temperature) and auditory (acoustic structure of copulation calls) modalities are also informative about the timing of ovulation in red-capped mangabeys (Cercocebus torquatus). Over 4 months, we collected standardized photographs, thermal images, audio recordings, endocrine (progesterone) and behavioral data from a captive group of six adult females and one resident male. We analyzed variation in swelling size, swelling skin temperature, and temporal and spectral parameters of female copulation calls according to the timing of ovulation (N = 15 cycles). Swelling size, but not temperature, varied with the likelihood of ovulation. Copulation calls produced close to ovulation were hoarser, showing a lower harmonic-to-noise ratio and higher entropy. We found no evidence that thermal or auditory traits influenced male inspection toward females or the likelihood that they engaged in a second mating. These findings suggest that, in this population, ovulatory signaling is primarily unimodal (visual), although such a system could operate within a broader multimodal framework of female reproductive signaling. Our study, while deserving further extension, provides novel insights into the relative contribution of different modalities to ovulatory communication in non-human primates.

ABSTRACTSpecies occupying small habitat patches and exhibiting behavioral and ecological flexibility are more likely to persist in fragmented landscapes. However, when isolated populations are not self‐sustaining in the long term, translocation may be required, making an understanding of their behavior critical. Howler monkeys (Alouatta spp.) show high tolerance to habitat restriction, which has been linked to a highly folivorous diet and the exploitation of non‐tree plant and non‐native species as food sources. We assessed how the size of the habitat patch influences home range size, day range, time spent feeding, young leaf and fruit consumption, and diet richness, the relationships between these behaviors, and the effect of group size and study length on them using Generalized Linear Mixed Models and full model averaging based on a dataset of 97 studies conducted at 62 locations on the behavior of 124 groups representing nine species. Habitat patch size predicted home range size, which showed a positive effect on fruit consumption. Diet richness increased with increasing mean day range. No variable predicted day range, feeding time, and young leaf consumption. The limited and uncertain predictive power of habitat patch size for most variables reflect the unpredictability of the behavioral and ecological responses of howler monkeys to varying conditions of habitat quality. Our findings are consistent with the possibility that the behavioral flexibility enabling howler groups to survive in small, isolated, low quality habitat patches could enhance their value in metapopulation management strategies aimed at promoting long‐term persistence of the species in human‐modified landscapes.

Relocation and housing transitions are routine in captive settings, including biomedical facilities, and can negatively affect welfare by increasing restriction and reducing control. This study tested whether desensitization to human activity reduces fear and reactivity in rhesus macaques (Macaca mulatta) during indoor husbandry procedures. Fifty-six macaques were assigned to a treatment group receiving structured desensitization training (mean ± SE: 8.4 ± 3.4 sessions) or to a control group with no training. Fear and behavioral reactivity were assessed using a modified Human Intruder Test (mHIT) at baseline (day 0), day 15, and day 30. The mHIT included five conditions with progressively increasing mild aversive stimuli, with responses scored for each condition. No baseline differences were detected when conditions were combined. Significant Group × Time interactions showed greater improvement from baseline in the treatment group (Day 15: β = 0.59, p < 0.001; Day 30: β = 0.71, p < 0.001), with estimated marginal mean differences of 0.63 and 0.75 mHIT units, indicating moderate to large effects. Condition-specific analyses showed the strongest effects in tasks involving direct human interaction, particularly the Lixit Rod condition, with additional improvement in the Hand Feeding condition. Although a baseline difference was present in Hand Feeding, it did not explain the greater improvement over time in the treatment group. These findings indicate that structured desensitization reduces reactivity to human-related stimuli and may facilitate adaptation to routine procedures following relocation.

Social behavior in primates varies widely within and across species, and growing work in behavioral genetics highlights the value of documenting sequence variation in neurobiologically relevant genes. However, for great apes, knowledge of individual genetic variation for behavior-associated loci remains limited. We characterized variation in the MAOA promoter VNTR and the OXTR SNP rs35062132 in 12 western lowland gorillas (Gorilla gorilla gorilla) and incorporated an exploratory comparison between genotypes and individual sociability. Sociability was quantified from 25 10-min focal follows per subject, including proximity, affiliative, and agonistic behaviors. We identified multiple MAOA VNTR genotypes, including a 0-repeat allele not previously reported in gorillas, indicating greater regulatory-region diversity than has been described for this species. No polymorphism was detected at OXTR rs35062132, although several fixed differences from other great ape species were identified at nearby nucleotide positions. Behavioral observations revealed individual differences in sociability; however, the presence of multiple previously undescribed MAOA VNTR genotypes with unknown functional consequences limited interpretability of genotype-behavior associations. We provide the first detailed description of MAOA promoter variation in gorillas and demonstrate sequence conservation in the OXTR region analyzed. These data underscore the importance of future research on gorilla social variation and comparative primate genomics.

Madagascar is a biodiversity hotspot facing increasing anthropogenic pressures, with 95% of lemur species threatened with extinction. In addition to habitat loss and hunting, cyclones create treefall gaps with unknown effects on arboreal species. We examined the effect of Cyclone Eliakim, which struck Masoala National Park in March 2018 with sustained wind speeds reaching 151 km/h. We assessed whether lemur densities and their microhabitat niches changed in relation to the cyclone, and whether their distributions were related to treefall gaps. We conducted 110.42 km of transect walks for diurnal and 86.93 km for nocturnal lemurs between 2017 and 2022 in Andranobe, Masoala National Park, a region regularly hit by cyclones. Microhabitat data were recorded for each observation, and distance to the nearest canopy gap was used as a measure of association with treefall gaps. Densities of Varecia rubra, Eulemur albifrons, Avahi mooreorum, Lepilemur scottorum, and Microcebus sp. did not decline after the cyclone. Species niche separation was strongest directly after the cyclone (suggesting intensified competition over limited resources) and relaxed progressively as the forest recovered. Gap size increased after the cyclone and decreased by 59.9% 4.5 years later, indicating progressive canopy closure. Large diurnal lemurs were positively associated with gaps > 150 m2, likely reflecting increased food availability in sun-exposed areas. Small nocturnal lemurs were positively associated with small gaps (< 150 m2) but avoided larger gaps, possibly due to aerial predator risk. These data aid our understanding of species interactions and ecosystem dynamics under climate-driven habitat change.

Yellow fever (YF) outbreaks and anthropogenic fires are major sources of mortality in Neotropical primates, yet their legacy effects on population structure and reproductive output remain poorly quantified. We conducted a comparative assessment of black and gold howler monkey population (Alouatta caraya) across three population contexts in northeastern Argentina: (1) Yellow fever-affected, (2) Yellow fever-free populations, (3) a fire-affected population in Iberá wetlands. Group size was similar across sites, with a median of 9 individuals (range: 3-15). Multimale-multifemale groups predominated across all populations (76%-94%), and adult sex ratios were relatively balanced across sites, ranging from 1.4:1 to 1.6:1 adult females per adult males. Reproductive indicators were consistent among populations, averaging 1.4 immatures per adult female, while infant production ranged from 0.2 to 0.5 infants per adult female across sites. We recorded 60 births, primarily concentrated in autumn. YF-affected sites, which maintain low population densities (0.33 ind/ha), included social units as small as three individuals, despite an overall demographic structure comparable to that of unaffected populations. In contrast, the fire-affected site exhibited a higher proportion of subadult males (28%), consistent with a potential crowding effect (2.22 ind/ha) and dispersal limitation in recently burned remnants. Our findings suggest that A. caraya maintains stable social structures and reproductive output despite disturbances, highlighting demographic resilience. However, persistent low densities in YF-affected sites, altered dispersal patterns in burned landscapes, and the potential effects of isolation and habitat degradation underscore the need for long-term monitoring to evaluate population viability under increasing environmental uncertainty and ongoing landscape change.

ABSTRACTIn 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.