Sleep is the longest and most continuous behavioral phase in the 24 h cycle of mammals. However, selection of postures, substrates, and tree parts during sleep has not been adequately explored, as well as their evolutionary consequences. The present study investigates postural behavior, substrate, and tree part use during sleep in three howler species (A. palliata, A. macconnelli, and A. caraya) in Nicaragua, French Guiana, and Argentina. All three species were consistent in the use of a crouch.

Reactions to predators vary a lot in primates and can be passive (hiding, fleeing) or active (mobbing, alarm calls). Due to their secretive lifestyle, Neotropical titi monkeys are thought to use mainly passive crypsis and hiding as anti-predator responses. Predator mobbing has been reported only for one titi species, Callicebus nigrifrons. We report mobbing of an ocelot and Boa constrictor in red titi monkeys and Plecturocebus cupreus, and alarm calling as a reaction to tayras and raptors.

These data come from the major study on gut passage with two primate species (Callicebus coimbrai and Callicebus barbarabrownae) enclosed in the Zoobotanical Park localized in the north-eastern Brazil. During the sampling period, we have decided to obtain self-anointing and laterality data. Due to the presence of large glands in C. coimbrai and C. barbarabrownae chests, we cautiously suggest that the use of Bauhinia may be linked to olfactory communication.

We report observations fur-rubbing with leaves from the spiked pepper plant, Piper aduncum, in the San Martín titi monkey, Callicebus oenanthe. As leaf extracts from this plant include insecticidal compounds, we interpret this behaviour as a defense against ectoparasites. Our observations expand the number of primate species for which this kind of self-medication is reported.

Here we report two encounters between olive baboons (Papio anubis) and crowned eagles (Stephanoaetus coronatus), a potential predator, at Lake Manyara National Park, Tanzania. On both events, baboons gave alarm calls while infants got close to adults and juveniles ran to cover. Adult males approached the eagles and chased them away. The baboons’ reactions indeed support the assumption that crowned eagles pose a threat, at least for juvenile baboons.

Coalitions are a specific case of cooperative competition and have been explained by various factors like partner availability, distribution of fighting ability, or cost of coordination. We investigated if age is an important factor influencing coalition formation and, specifically, if males switch from a solo strategy to a cooperative one after reaching post-prime age. We found that older males formed more coalitions than younger ones, stressing the importance of age in cooperative competition.

We report on extremely rare events of group eviction and eventually lethal aggression in a group of ring-tailed lemurs (Lemur catta) that were targeted against the two highest-ranking females. These events erupted after an infanticide by the highest-ranking female directed at the offspring of a subordinate. We suggest that this aggressive changeover of power between two matrilines was based on the growing group size and was an act of female reproductive competition during birth season.

We describe the acquisition, sharing and consumption of meat by wild Guinea baboons. Males were the hunters and shared meat passively only with females in their social and reproductive units. Females were able to acquire meat from sharing episodes and by scavenging from their male social partners. The presence of existing social bonds, rather than short-term exchanges of meat for sex, is likely a driving factor in the occurrence of meat sharing between males and females in this species.

We report the first case of putative empathic response in titi monkeys (Callibebus). Pair bonds between males and females are typically strong, with substantial time spent grooming and tail twining. In an intriguing and unexpected observation we recorded an injured adult out-group male travelling with a neighbouring group. The group appeared to adapt travel patterns to allow him to accompany them, provided pro-social behaviour such as grooming and tolerated his presence at their sleeping site