Long-distance vocalizations are crucial for facilitating group coordination and maintaining social relationships in many primates by allowing individuals to exchange information when visual contact is limited. These signals may convey information about both individual identity and social status. We investigated whether lost calls, the primary long-distance contact call of white-faced capuchins (Cebus imitator), vary according to caller identity and male dominance rank (alpha vs. subordinate). We quantified multiple acoustic features from 749 lost calls recorded from 24 males and analyzed acoustic variation using permutation-based classification, Random Forest models, and linear mixed-effects analyses. Lost calls showed strong evidence of individual distinctiveness, with classification accuracy significantly above chance and several acoustic features exhibiting greater between-individual than within-individual variation. In contrast, we found little evidence of dominance-related acoustic variation. Multivariate classification of rank did not significantly exceed chance expectations, and univariate analyses revealed no significant differences in fundamental frequency or call duration, with only a modest difference in formant dispersion. These findings indicate that lost calls primarily reflect individual differences rather than dominance-related variation and suggest that receivers infer socially relevant information through individual recognition and prior social knowledge rather than direct acoustic cues to dominance rank. Our results support the importance of vocal individuality in facilitating long-distance communication in socially complex primates.
Primate vocal communication complexity is driven by phylogenetic and ecological factors, as well as social complexity. While group size is a well-studied predictor of social complexity in animal communication, the influence of other key social components, such as mating systems and social organization, remains less clear. We used a systematic review and mixed models to test the influence of group size, mating system, and social organization on four measures of vocal complexity: number of call types, number of syllables, number of calls with multiple syllables, and number of alarm calls. We identified 53 publications concerning 46 primate species. We found a complex relationship between social and vocal complexity. Monogamous species produced fewer syllables than polygynous, polygynandrous, and flexible-mating species. Likewise, dispersed-solitary species produced fewer syllables than species living in some forms of group-based social organization. In contrast, repertoire size, number of combined calls, and number of alarm calls were not significantly associated with the social predictors examined. These results suggest that syllable repertoire may be particularly associated with social complexity, especially mating system and social organization. The social traits are also closely related to ecological factors, such as food distribution, habitat type, and predator risk. Future studies incorporating ecological factors are important for a better understanding of these individual and combined effects on vocal evolution.
Understanding how animals adjust their physiological processes to environmental variation is essential for predicting their resilience under future climate change. Thyroid hormones, particularly triiodothyronine (T3), play key roles in metabolism, thermoregulation, and seasonal energy balance, yet remain understudied in nonhuman primates, especially nocturnal strepsirrhines. We aimed to 1) evaluate an enzyme immunoassay (EIA) for measuring fecal triiodothyronine metabolites (fTM) in the thick-tailed greater galago (Otolemur crassicaudatus), and 2) examine environmental and reproductive drivers of seasonal fTM variation in a free-ranging population. We collected fecal samples (N = 126) for 18 months across four seasons (two dry and two wet). We used a thyroid-stimulating hormone (TSH) challenge to assess the EIA’s ability to detect changes in fTM concentrations. We used linear mixed models to test effects of climate, resource availability and reproductive stage on fTM. The TSH challenge provided preliminary support for the assay: fTM levels in the female peaked at 6.5 h, whereas the male's postinjection peak occurred at approximately 10 h. fTM concentrations increased with ambient temperature and rainfall but were not related to insect, seed, or gum availability and were highest during early lactation in both sexes; because reproduction is seasonal, we could not separate climatic and reproductive effects. Our findings suggest that thyroid activity in galagos varies with seasonal climatic conditions in both sexes, rather than increasing in the cold as expected for a thermoregulatory role, highlighting the value of noninvasive thyroid monitoring for understanding how primates cope physiologically with seasonal environments.
Late-gestation ultrasonography was performed without anesthesia in captive Ateles belzebuth. Positive reinforcement enabled rapid, low-stress fetal assessment (<3 min). Fetal viability and biometric parameters (heart, chest, abdomen and head) were documented. Noninvasive ultrasonography supports conservation breeding of endangered primates.
