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Morphological adaptations related to food processing generally reflect those elements of the diet that represent the greatest biomechanical challenge or that numerically dominate the diet. However, in periods of the annual cycle when the availability of such foods is low, items to which a species has low apparent morphological adaptation may be included in the diet. Here we test the responses of a diet-specialist primate to limitations in the supply of the resource it is specialized to exploit. Uacaris are primarily predators of immature seeds, in seasonally flooded forests in Amazonian Brazil, and have dental specializations to open hard-shelled fruits. We investigated the importance of arthropods in the diet of golden-backed uacaris (Cacajao melanocephalus ouakary), examining their seasonal importance in the uacari diet, and the ways C. m. ouakary used to access them. Using scan and ad libitum sampling of feeding and phenology from botanical study plots to assess fruit availability, we conducted an 18-mo study in Jau National Park, Amazonas State, Brazil. We recorded arthropod predation 298 times, with Cacajao melanocephalus ouakary feeding on 26 invertebrate taxa in ≥11 families and 9 different orders. Uacaris extracted wood-boring beetles dentally from rotting wood and smaller larvae from twigs, stems, and petioles, but this food class did not predominate. This food class (encapsulated foods) constituted 23.4 % of the arthropod records. The majority of arthropod food items were either manually removed from substrates (ants, beetle larvae, caterpillars, fulgorid bugs, grasshoppers, mayflies, spiders, termites, wasps, and a whip-scorpion) or plucked from the air (volant Lepidoptera). Uacaris appeared to avoid toxic caterpillars. Insectivory was most frequent when fruit and seeds were least available. Arthropods seem to be seasonally important to this primate, supplementing or making up for shortfalls in the hard fruits and immature seeds for which uacaris have highly developed dental, and possibly intestinal, adaptations.

Sexual selection has driven the evolution and elaboration of a wide variety of displays and ornaments in male nonhuman primates, including capes, cheek flanges, and sexual coloration. Among the most sexually dimorphic of all primates is the drill (Mandrillus leucophaeus), the males of which can be 3 times the mass of females, possess large canines, and exhibit extremely bright sexual skin coloration. However, the function of male coloration in this species has never been examined. Here, we present data on male color (measured objectively using digital photography), dominance rank, measures of male-female association, and key sexual behaviors, of adult male drills (n = 17) living in four semi free-ranging enclosures at the Drill Rehabilitation and Breeding Center in Nigeria. We test the hypothesis that male coloration is a badge of status, indicating dominance rank, and the hypothesis that male coloration attracts females. We found that male coloration did indicate rank, and that high ranking, strongly colored males were more likely to associate with adult females, and more specifically with fully tumescent females. These males also engaged in more sexual activity. However, measures of male-female association and sexual behaviors were not related to male color once rank had been taken into consideration; i.e., for males of a given rank, females did not prefer those that were more colorful. We discuss the results in light of what is known about the wild drill social system, in which unfamiliar individuals may come together in “supergroups,” and in which quality indicators of competitive ability may be particularly important.

We compared parasitic infection in a crop-raiding and a wild-foraging troop of olive baboons, Papio anubis, in Gashaka Gumti National Park, Nigeria, to quantify how crop raiding may have influenced primate-parasite interactions. We recovered gastrointestinal parasites from fecal samples from all adult individuals in both troops and processed them via formal-ether sedimentation. We compared parasitic species richness, prevalence, output, and load across troops. We recovered 9 parasite taxa. The wild-foraging troop had a significantly higher mean output than the crop-raiding troop for Physaloptera sp., Trichuris sp., and also a significantly higher total helminth load. The crop-raiding troop had a significantly higher mean output for the protozoan Balantidium coli and also showed a higher parasitic species richness, with 9 species recovered compared to the 7 recorded for the wild-foraging individuals. The changes in nutritional intake, behavior, and human proximity caused by crop raiding may have important epidemiological impacts on wild primate populations, and the nature of such impacts may vary across different taxa of parasites.

Few mammalian orders carry their infants clinging to the mother's fur. I investigated the evolution of carrying behavior in primates and the life-history and ecological correlates of infant care patterns. Primates are ideal for the study as there is variation in infant care patterns. Primate infants are left hidden in nests or parked in trees, both of which strategies I term parking, and are carried orally or ride clinging to the mother's fur: riding. Infant carrying has evolved several times in the Primates and, once evolved, it has been conserved. Significant energetic costs of riding are indicated as riding species maintain smaller home ranges than those of non-riders of the same body size. With body size and phylogenetic influences taken into account, riders appear to incur a reproductive cost by weaning and breeding later than parkers. Although riders do not have lower birth rates than those of parkers, their later age at first reproduction leads to their having a lower reproductive rate, measured by the intrinsic rate of population increase. Precociality of infants is not correlated with either riding or nesting behavior. Although non-nesting species have larger litter sizes, their infants are not significantly smaller, nor are their neonatal brains relatively smaller. Although riding may have some energetic and reproductive costs, its repeated evolution in the Primates suggests that it also has some benefits, the most likely being a reduced mortality risk for carried infants.

Allometric methods are used to investigate the life history patterns of New World monkeys. These patterns are compared to those found in other haplorhines and links with ecology are explored. The life history characteristics of the cebid monkeys suggest that these species are primarily slow breeding and slow developing for primates of their size. I suggest that these characteristics arose during a long period of adaptation to stable rainforest habitats. The capuchins and squirrel monkeys are a notable exception to the general rule that genera found outside primary forests will have a “fast” life history. In the marmosets and tamarins selection for small size and high birth rate has occurred, probably as a result of their adapting to more secondary habitats. It is this selection for rapid breeding, combined with the preadaptation of paternal care, that has probably led to twinning in these species. The evidence presented indicates that it is unlikely that twinning arose as a direct result of the mechanical constraints of small size but is more probably due to selection for increased reproductive output.