American Journal of Primatology最新文献

Assessments of nonhuman primate (NHP) affiliation are typically restricted to daytime behavior. There is, however, a growing interest in understanding NHP behavior and welfare over the 24-h period. To assess the sleep quality and sociality of rhesus macaques, we measured the time it took pair-housed macaques to fall asleep (sleep latency), the proportion of time macaques spent asleep at night, and whether these behaviors were mediated by sex and daytime affiliation. We studied the behavior of six female–female and six male–male rhesus macaque pairs (24 animals). Five daytime observations were done cage-side per subject, and nighttime recordings captured 5 nights/pair. The pairs of macaques fell asleep in a coordinated fashion—the sleep latency of cagemates was significantly correlated—but males fell asleep almost three times faster than females. Despite the sex difference in time to fall asleep, there was no difference in the proportion of the night that males and females were observed asleep, and all pairs were observed to be asleep the majority of the time at night. At night, both male and female macaques were significantly more likely to be asleep than awake when in contact with their partner and they spent a greater proportion of time in proximity to their cagemate at night than during the day. This study emphasizes the value of co-housing NHP for their wellbeing and given our finding that daytime sociality did not predict nighttime social behavior, highlights the need to consider the behavior of NHP over 24-h.

Today's students are tomorrow's leading scholars. With effective mentoring, they will continue to address key issues in the critical work that will conserve and protect our closest living relatives—our fellow primates. The articles presented as part of this special issue on student-led work in primatology reflect the tremendous breadth of the field, covering such broad topics as diet, reproduction, conservation, husbandry, physiology, social behavior, welfare, and cognition. These studies were conducted in both field and captive settings, reflecting the diversity of contexts in which primates are being actively studied today. Whereas some of the work focuses on basic research questions, all of the papers have the potential to impact the lives of primates today and into the uncertain future. We hope that cultivating this collection of student-led work will highlight the fertility and importance of work in this field and inspire established researchers to continue to invest in mentoring the next generation of scientists.

Social inequality in primates is marked by dominance-based resource monopolization. Yet, high-ranking individuals sometimes yield to lower-ranking individuals to promote group stability, indicative of behavioral social tolerance. Social tolerance is dynamic and is shaped by resource availability, group structure, hierarchy steepness and kinship. Increasing social tolerance around resource access may promote group stability and improve individual wellbeing. The multifaceted nature of behavioral social tolerance means we still lack a full understanding of its temporal, individual, and social drivers and whether modifications in resource distribution promote or hinder tolerant behavior in unequal societies. We tested whether decentralizing food resources improved behavioral social tolerance via two measures: reduced aggression and increased co-feeding through the study of a large group of outdoor-housed rhesus macaques (Macaca mulatta), a macaque species typified by low social tolerance. We assessed whether reduced resource competition and time of day influenced co-feeding behavior, and whether investment in grooming afforded future social tolerance. We found that, relative to a baseline and follow-up period with centralized food resources, distributed resources promoted social tolerance, but this was modulated by dominance rank. High-ranking individuals may exhibit greater behavioral flexibility while low-ranking individuals are afforded increased access to resources through reduced competition. We found temporal variation in co-feeding behavior with more co-feeding occurring in the afternoon. Lastly, we found limited evidence to suggest individuals groomed to afford future co-feeding tolerance. Combined, these results suggest that increased resource distribution in captive populations could provide a social benefit and contribute positively to health and well-being.

Capuchin monkeys are known for their object manipulation skills, but little is known about that in physically impaired individuals. Several wild populations use tools primarily for foraging, but such behavior is rarely reported for drinking water. In urban fragments, objects discarded are available for manipulation, and water can be scarce. Therefore, the study of object manipulation in such contexts illuminates how human-made artifacts and tools can be used to deal with anthropogenic opportunities and resource constraints. We investigated object manipulation and tool use in urban robust capuchin monkeys in Foz do Iguaçu, southern Brazil. We aimed to understand how much these animals invest their activities in object manipulation, the origin of the materials they use, the types of manipulations and tools employed, and whether the frequency of these behaviors differs among sex and age classes, as well as between dry and wet months. We described a new technique of tool use in capuchin monkeys, involving the use of containers to drink water, and a stronger tendency to use tools by an injured male juvenile with a hand deficiency. Over the course of 865 h of observation, we noted that tools were simple, infrequently used, and most were exhibited by juveniles, primarily by the injured individual, to access water during the driest periods. Containers to collect water emerged as the most frequent technique. Capuchins took advantage of human-made receptacles from nearby construction sites. Our findings contribute to understanding the flexibility of capuchins' tool use in response to urban novelties and pressures.

The responses of nonhuman primates towards conspecific deaths in the wild, and the activities of carnivores scavenging the corpses, are different but interconnected thanatological and ecological aspects of wildlife mortality. We report the first thanatological events observed in a wild, multilevel group of Myanmar or black snub-nosed monkeys (Rhinopithecus strykeri [R. strykeri]) and mesocarnivores scavenging on a monkey carcass in the Pianma region, near the China-Myanmar border. We detected two freshly deceased carcasses during field surveys. The group members visited the location of their recently deceased conspecific twice and variously looked down at the carcass, emitted alarm calls and unusual contact calls, hugged social partners and prevented approaches by individuals from other social units. These behaviors suggest strong bonds and emotional reactions to the death of a companion in R. strykeri. Infrared camera trapping revealed the Siberian weasel (Mustela sibirica) as the principal scavenger on the carcass, followed by the yellow-throated marten (Martes flavigula). Siberian weasels showed greater activity levels and time spent feeding on the R. strykeri carcass when it was fresh, while remaining vigilant for potential competitors and predators. After the carcass was largely consumed and decayed, both frequency and duration of feeding and vigilance behaviors decreased.

Indirect reciprocity consists of performing an act that benefits a recipient while increasing the chances of receiving cooperation from a bystander. While widespread in humans, evidence of indirect reciprocity in nonhuman animals is scarce. Indirect reciprocity may involve an audience effect if cooperation increases in the presence of an audience. We investigated indirect reciprocity and audience effects in wild Geoffroy's spider monkeys (Ateles geoffroyi). Using survival analysis, we assessed whether individuals who had recently groomed others tended to be groomed more by other group members (indirect reciprocity), and whether individuals tended to groom more when surrounded by bystanders (audience effect). We found no evidence for indirect reciprocity: individuals did not receive more grooming in the 10 min after they had recently groomed others. We also found that the presence of an audience did not increase the likelihood of grooming. Actually, male spider monkeys were less likely to groom one another in the presence of other males. We found no evidence for audience effects associated with the presence of adult males on the likelihood of grooming by subadult males. Our results suggest indirect reciprocity is absent in spider monkeys, at least in the 10-min timeframe we investigated, and contribute to the limited literature on indirect reciprocity in nonhuman animals.

Deforestation, habitat loss, and fragmentation impact the ecology, genetics, and health of many wildlife species, including primate populations. We evaluated the association between landscape characteristics and demographic features of Alouatta caraya howler monkeys in human-modified rural areas of Pampa del Indio in the Argentine humid Chaco. Landscape metrics were obtained from a supervised classification of a Landsat 8 image based on different kinds of exploited forests. Four times over a 2-year period, we surveyed howler monkey groups using loud calls heard at 113 listening posts in three habitat types: gallery woodland, riparian, and quebrachal hardwood forests. We also determined the age and sex composition of 31 groups through observation. A Bayesian spatial generalized linear mixed model using Integrated Nested Laplace Approximation with a Stochastic Partial Differential Equation to account for spatial dependence revealed a negative association between howler monkey group counts and prime habitat availability (i.e., old-growth forest). Howler group size was positively associated with patch density, while both the immature-to-adult female ratio and group size were negatively associated with the division index of prime habitat. Despite the apparent ability of howler monkeys to cope with habitat modification, prime habitat availability is crucial to the long-term conservation of A. caraya. Innovative landscape management strategies are required to ensure the long-term persistence of howler monkeys in human-modified environments under rapid change in the Gran Chaco eco-region.

Increased fluctuating asymmetry, or random differences between right and left sides, has been associated with developmental stress or developmental instability. This study examines fluctuating asymmetry (FA) of mesio-distal and bucco-lingual dimensions of deciduous maxillary molars (m¹, m²), and permanent maxillary premolars and molars (P³, P⁴, M¹, M²) of 466 rhesus macaques (Macaca mulatta) born between 1950 and 2018 from Cayo Santiago (CS), Puerto Rico. All included individuals were of known age, sex, birth year, and matriline. We assess whether a secular trend occurs in FA over a 68-year period, sex differences in FA, and whether environmental or management factors in the colony history resulted in decreased FA. Regression of FA on birth year tested for a secular trend in FA. A mixed-model two-way analysis of variance was used to test for the influence of food supplementation, tetanus vaccination and hurricane experience during dental development on FA. Differences across matrilines in response to the management or environmental factors were tested by ANOVA. There was no significant secular trend in FA. There was limited reduction of FA with implementation of the high protein diet, and limited support for the decreased FA associated with the implementation of tetanus vaccination. There is also limited difference in dental FA associated with exposure to a hurricane during dental development. Matrilineal differences in FA were observed for several teeth. The free-ranging environment of Cayo Santiago is a complex environment, with many factors influencing the development of young rhesus macaques. While the introduction of a high protein diet or the implementation of a tetanus vaccination program may have improved individual health overall, there are likely other factors that may cause developmental stress and result in dental FA.