American Journal of Primatology最新文献

The nighttime behavior of diurnal species is a “black box.” Although diurnal animals spend approximately half their lives in the dark, research has, for too long, relied on the simplifying assumption that what we can't observe isn't important. Advances in our ability to monitor nighttime behavior reveal that this is incorrect; essential biological and behavioral processes play out in the dark which are critical for understanding a species' ecology and evolution. We conducted our study from November 2021 to January 2022, using noninvasive 4G solar-powered night-vision cameras to quantitatively assess the impact of environmental and social factors on the diel activity patterns of wild Tibetan macaques at Mt. Huangshan, China. We find that Tibetan macaques maintain high levels of sleep throughout the night, as is typical for diurnal animals. However, non-sleep activity still accounted for 18.28% ± 0.45% of the total nighttime period, with activity occurring throughout the night. Notably, there was a peak in activity at midnight, including resting, movement, and social. Low temperatures significantly reduced daytime activity levels, while increasing nighttime activity, indicating that extreme temperatures have divergent impacts on activity levels during the day versus the night. Additionally, social activities were more frequent among females during the day, whereas males were more socially active at night. The distinct patterns of social activities during the day and night highlight the crucial role of social factors in nocturnal activities. The night-vision cameras have proven to be an effective research tool, allowing for a deeper understanding of primate behavior patterns and social structures. This provides new avenues for future research into the drivers of nighttime behavioral patterns across species.

Colors are an important signal for many primate species and have the potential to influence behavior and cognition. Primates may consciously or unconsciously prioritize their attention toward certain color stimuli to quickly identify consequential events, conspecifics, or resources. On the other hand, primates' color preferences can be modulated by memory, experiences, and affective responses. Few studies have explored the multifaceted nature of attention to colors in primate species that vary in their socioecologies and phenotypes, both of which may influence their responses to specific colors. The colors that rapidly capture primates' attention, and those they prefer, thus remain poorly understood. In a series of touchscreen experiments, we investigated responses to 9 perceptually distinct colored squares by 7 chimpanzees (Pan troglodytes), 11 gorillas (Gorilla gorilla gorilla), and 10 Japanese macaques (Macaca fuscata). We controlled for contextual cues known to influence color responses and assessed attentional biases using a dot probe task (Experiment 1) and preferences using a two-item forced-choice task (Experiments 2 and 3). In Experiment 1, we found that chimpanzees and gorillas showed the strongest attentional bias toward black, whereas the Japanese macaques showed the strongest bias toward red. These attentional biases suggest a potential relationship between species coloration and their attention to colors. In Experiments 2 and 3, all three species preferentially selected red, with Japanese macaques showing the strongest preference, supporting earlier findings that highlighted red as a particularly salient color to primates. Future research is needed to investigate the role of prior experience on primates' responses to colors.

Traditional qualitative behavioral assessments (QBAs) employ a unique whole-animal approach to measure animal welfare with a focus on affective elements. QBAs require comprehensive validation including reliability across multiple raters, subjects, and institutions, as well as consistency with other validated assessment measures. In 2016, the Detroit Zoological Society developed and began internally validating the Gorilla Behavioral Assessment Tool (GBAT), followed by internal applications of a revised GBAT in 2021. This study continues these validation efforts through the multi-institutional application of the GBAT in baseline conditions. Five zoological institutions participated in this study, creating a study population of 15 adult male western lowland gorillas (Gorilla gorilla gorilla) and more than 40 staff. Care staff collected fecal samples from each gorilla, and two staff from each institution completed the GBAT for each gorilla daily. Three of the five institutions collected focal behavioral data. We calculated inter-rater reliability using Gwet's AC₂, establishing near-perfect reliability across all tested items. We found no significant variation in reliability between institutions. We used the behavioral data and fecal glucocorticoid metabolites for construct validation. A combination of Spearman's correlations and generalized linear mixed models demonstrated statistically significant relationships between seven of the 12 tested GBAT items and other established measures. Integration of physical and behavioral indicators of welfare alongside affective indicators alters the GBAT from a traditional QBA into what we propose as a mixed or M-QBA. Our work demonstrates how an M-QBA allows for a more comprehensive assessment of animal welfare with implications for broader research applications.

Rhesus macaques (Macaca mulatta) have long been used as a model for the evolution of some aspects of human social behavior and they are among the most completely understood species of the macaque genus. Rhesus macaques have a despotic dominance hierarchy with a well-documented facial display repertoire. However, we know little about the ontogenetic changes in gross facial musculature and how this might relate to corresponding facial display behavior. In an effort to illuminate our understanding, we dissected facial masks from 13 M. mulatta cadavers that died naturally, shortly after birth or were stillborn, and we compared these results to those from adult rhesus macaques. Results reveal that, unlike the adults in the present study, infant rhesus macaques have extrinsic external ear muscles and muscles associated with the lower lip that are very gracile and poorly developed. Musculature associated with the upper lip and nares are well developed, individually distinct, and robust, like those of the adults in our sample and adult M. mulatta. However, we were unable to locate the zygomaticus major muscle in any fetal/infant sample. These results may reflect simple variation in mimetic muscle ontogeny, differences related to facial allometry, or they could reflect a behaviorally meaningful adaptation to different life stages of macaque ontogeny.

Laboratory studies have broadened our understanding of primate arboreal locomotor biomechanics and adaptation but are necessarily limited in species availability and substrate complexity. In this field study, we filmed the locomotion of 11 species of platyrrhines (Ecuador and Costa Rica; n = 1234 strides) and remotely measured substrate diameter and orientation. We then explored ecological and phylogenetic influences on quadrupedal kinematics in multivariate space using redundancy analysis combined with variation partitioning. Among all species, phylogenetic relatedness more strongly influenced quadrupedal kinematics than variation in substrate. Callitrichines were maximally divergent from other taxa, driven by their preferred use of higher speed asymmetrical gaits. Pitheciids were also distinctive in their use of lower limb phases, including lateral sequence gaits. The biomechanical implications of interspecific differences in body mass and limb proportions account for a substantial portion of the phylogenetic-based variation. Body mass and kinematic variation were inversely related–whereas the larger taxa (atelids) were relatively restricted in kinematic space, and preferred more stable, symmetrical gaits, the smallest species (callitrichines) used faster, more asymmetrical and less cautious gaits along with symmetrical gaits. Intermembral index had a positive relationship with limb phase, consistent with higher limb phases in atelines compared to pitheciids. Substrate alone accounted for only 2% of kinematic variation among all taxa, with substrate orientation influencing kinematics more than diameter. Substrate effects, though weak, were generally consistent with predictions and with previous laboratory and field-based research. Excluding callitrichines and asymmetrical gaits, the influence of substrate alone remained low (2%), and the phylogenetic signal dropped from 31% to 8%. The substantial residual kinematic variation may be attributable to substrate or morphological variables not measured here, but could also reflect basic biomechanical patterns shared by all taxa that serve them well when moving arboreally, regardless of the challenges provided by any particular substrate.

Competition within primate groups often translates to a social hierarchy, with high-rank individuals gaining privileged access to resources, especially food. Golden snub-nosed monkeys Rhinopithecus roxellana live in a multi-level society, with multiple one-male units (OMUs), each containing a single adult male and several females, forming a breeding-band. High-rank males have increased access to high-value foods and spend less time feeding and more time being groomed by females, potentially enhancing social cohesion within their OMUs. The adults of each OMU mainly feed and socialize together, with food competition predominantly acting at the OMU level. We thus predicted that adult females by association attain the rank and feeding privileges of their OMU leader males, and make similar time-budget trade-offs. By food-provisioning a wild breeding-band during winter and spring, when natural foods are abundant or limited, respectively, we found that females of high-rank OMUs ate more provisioned foods at higher rates, especially during winter when provisioned foods had increased value. In winter, females of low-rank OMUs fed for longer on natural foods and females of high-rank OMUs longer on provisioned foods. Females of high-rank OMUs spent longer being groomed by other OMU members, especially during winter. Our results are consistent with females attaining the feeding privileges of their OMU leader male, enhanced during winter due to increased value of provisioned foods, high thermal demands, and reduced natural food availability. Importantly, the feeding privileges attained by females of high rank OMUs were less pronounced than those previously found for leader males, possibly due to higher tolerance between females of different OMUs. We suggest that behavioral time-budget effects of food competition in female R. roxellana enhance cohesion in high-rank OMUs, contributing to OMU integrity and, hence, the social structure of this multi-level society.

The high energy demands of primates during pregnancy and lactation often limit their breeding success due to the availability of food resources. Until now, few studies have focused on the effects of continuous provisioning on primate reproduction. To assess the impact of continuous provisioning on breeding success, we collected data on female reproductive status (primiparous or multiparous), maternal age of births, births, deaths, and sex of infants in a free-ranging semi-provisioned band (FSB) of Rhinopithecus bieti in China from 2010 to 2023. Our results indicate that provisioning significantly increases infant survival. After 8 years of provisioning, 11 females began a pattern of giving birth to infants in two continuous years, skipping reproduction in the third year, and resuming in the fourth year. Continuous provisioning led to a year-by-year reduction in the interbirth interval (IBI) and a gradual decrease in the primiparous age. The percentage of consecutively breeding females (CBFs) and their offspring increased annually and with the mother's ages. Conversely, the percentage of offspring from non-consecutively breeding females (NBFs) decreased over time and with maternal age. Each CBF annually produced 9.4% more infants compared to NBFs. Compared to NBFs, CBFs had a higher maternal age at births, a higher fertility rate, a higher infant survival rate, and a 11.7% shorter IBI. Furthermore, compared to the non-provisioned wild band (NPB), females in the FSB gave birth 128 days earlier, had an 18.9% annual increase in the number of offspring per female, and showed 1.2 times higher infant survival beyond 12 months. Our study demonstrates that provisioning significantly enhances reproductive success and population size. However, before promoting provisioning as a conservation tool to stabilize and recover endangered wildlife populations, it is essential to thoroughly evaluate its potential risks, such as nutritional imbalances, increased stress, and the transmission of diseases.

For decades, welfare scientists have focused on investigating and mitigating the abnormal behaviors—including repetitive stereotypic behaviors and abnormal stances/postures—displayed by chimpanzees residing in professionally managed settings. In an effort to design feasible and practical welfare assessments, researchers often pool abnormal behaviors into subcategories. However, this approach can result in the creation of heterogeneous subcategories comprised of behaviors that do not statistically co-occur. This study examined the co-occurrence of abnormal behaviors in 41 adult chimpanzees living in 16 facilities accredited by Association of Zoos and Aquariums. Specifically, we employed principal component analysis and regression analyses to investigate the following behaviors: self-directed hair pluck, idiosyncratic body manipulations (e.g., eye-poking), and idiosyncratic movements/postures (e.g., rocking). We found: (1) none of the behaviors loaded onto the same component, and (2) no significant relationships were discovered by performing the regression analyses. These findings suggest that self-directed hair pluck, idiosyncratic body manipulations, and idiosyncratic movements/postures are heterogeneous and should be scored separately in future studies of adult chimpanzees. Though this study cannot provide insight into the potential triggers for these specific behaviors, the lack of positive associations suggests that they may have unrelated triggers and treatments. Ultimately, future research should attempt to reduce and eliminate abnormal behaviors by introducing tailored interventions to the husbandry routine and/or environment. The findings of this study can be extended to other taxa. Specifically, welfare researchers should analyze individual abnormal behaviors separately, instead of forming subcategories of abnormal behaviors, unless behaviors are found to statistically co-occur.