Robbing and bartering (RB) is a behavioral practice anecdotally reported in free-ranging commensal macaques. It usually occurs in two steps: after taking inedible objects (e.g., glasses) from humans, the macaques appear to use them as tokens, returning them to humans in exchange for food. While extensively studied in captivity, our research is the first to investigate the object/food exchange between humans and primates in a natural setting. During a 4-month study in 2010, we used both focal and event sampling to record 201 RB events in a population of long-tailed macaques (Macaca fascicularis), including four neighboring groups ranging freely around Uluwatu Temple, Bali (Indonesia). In each group, we documented the RB frequency, prevalence and outcome, and tested the underpinning anthropogenic and demographic determinants. In line with the environmental opportunity hypothesis, we found a positive qualitative relation at the group level between time spent in tourist zones and RB frequency or prevalence. For two of the four groups, RB events were significantly more frequent when humans were more present in the environment. We also found qualitative partial support for the male-biased sex ratio hypothesis [i.e., RB was more frequent and prevalent in groups with higher ratios of (sub)adult males], whereas the group density hypothesis was not supported. This preliminary study showed that RB is a spontaneous, customary (in some groups), and enduring population-specific practice characterized by intergroup variation in Balinese macaques. As such, RB is a candidate for a new behavioral tradition in this species.

Worldwide, primates, and humans increasingly share habitats and often enter in conflict when primates thrive in human-dominated environments, calling for special management measures. Reproductive control is increasingly used to manage population growth but very few monitoring data are available. Therefore, the efficiency and implications of such programs require a careful examination. In the context of a contraception program in wild female long-tailed macaques in Ubud, Bali, conducted over four successive campaigns between 2017 and 2019, including 140 females (i.e., 41.9% of the reproductive females of the population in 2019), modifications of an endoscopic tubectomy procedure, a permanent sterilization method, clinical evaluation of this method, and the post-operative monitoring results of the neutered females after release are described. This surgical approach was applicable for pregnant females: 28.6% of the treated females were pregnant at the time of the surgery. The procedure used a single lateral port to reach and cauterize both oviducts in non-pregnant as well as in early to mid-term pregnant females. Pregnant females nearer to term required a second lateral port to access both oviducts masked by the size of the gravid uterus. Moreover, bipolar thermocauterization was utilized successfully without resection to realize the tubectomy. The average duration of the laparoscopic surgery was 14 min for non-pregnant females and 22 min for pregnant females. Animals were released 3 h 22 min in average following their capture. This short holding time, recommended for free-ranging primates, was made possible by the minimal invasiveness of the sterilization approach. A laparoscopic post-operative evaluation conducted on two patients during the following campaign confirmed that the oviducts were definitely disrupted and no longer patent. Moreover, no new pregnancies in sterilized females were recorded during the 3-year observation period. The survival rate of the treated females 6 months after sterilization was high (96.3%) with no major post-operative complications clinically recorded. Among females that were pregnant during surgery, 81.1% were confirmed to experience term delivery. This study demonstrates the safety and efficiency of endoscopic tubectomy, even for pregnant females, as a mean of wild macaques' population control.

Contraception is increasingly used to control wild animal populations. However, as reproductive condition influences social interactions in primates, the absence of new offspring could influence the females’ social integration. We studied two groups of wild macaques (Macaca fascicularis) including females recently sterilized in the Ubud Monkey Forest, Indonesia. We used social network analysis to examine female grooming and proximity networks and investigated the role of infant presence on social centrality and group connectivity, while controlling for the fertility status (sterilized N = 14, intact N = 34). We compared the ego networks of females experiencing different nursing conditions (young infant (YI) vs old infant (OI) vs non-nursing (NN) females). YI females were less central in the grooming network than other females while being more central in proximity networks, suggesting they could keep proximity within the group to protect their infant from hazards, while decreasing direct grooming interactions, involving potential risks such as kidnapping. The centrality of sterilized and intact females was similar, except for the proximity network where sterilized females had more partners and a better group connectivity. These results confirm the influence of nursing condition in female macaque social networks and did not show any negative short-term effects of sterilization on social integration.