In many areas of The Gambia, West Africa, population crowding in a degraded environment has forced close interactions of diurnal primate species with humans. We assessed intestinal parasitic infection prevalence and diversity in 4 diurnal non-human primate (NHP) species, Chlorocebus sabaeus, Erythrocebus patas, Papio papio and Piliocolobus badius across 13 sampling sites. The effect of human activity, determined by the human activity index, and NHP group size on parasite richness was assessed using a generalized linear mixed model (GLMM). The most common protozoa identified were Entamoeba coli (30%) and Iodamoeba buetschlii (25%). The most common helminths were Strongyloides fuelleborni (11%), Oesophagostomum spp. (9%) and Trichuris trichiura (9%). Two of six (6%) Cyclospora spp. infections detected sequenced as Cyclospora cercopitheci (both in C. sabaeus). The more arboreal P. badius trended towards a lower prevalence of intestinal parasites, although this was not statistically significant (χ2 P = 0.105). Human activity or group size did not have any significant effect on parasite richness for P. badius (P = 0.161 and P = 0.603) or P. papio (P = 0.817 and P = 0.607, respectively). There were insufficient observations to fit a GLMM to E. patas or C. sabaeus. Our reports present the richness and diversity of intestinal parasites in 4 diurnal NHPs in The Gambia, West Africa. Despite desertification and habitat loss, our results indicate that the prevalence and diversity of intestinal parasites in Gambian NHPs are seemingly unaffected by human activity. Further investigation with a larger dataset is required to better elucidate these findings.

The COVID-19 pandemic led to unprecedented lockdowns with rippling impacts on the lives of humans and animals alike. Since zoos were among the first institutions to close during the pandemic, the lockdowns presented the opportunity to conduct a natural experiment examining the relationship between visitor presence and the welfare of zoo-housed animals. In this study, we assessed the welfare of six Sumatran orangutans (Pongo abelii) at Toronto Zoo both during and following the pandemic lockdowns. We compared behavioural and physiological indicators of welfare during a lockdown and after visitors were reintroduced. Specifically, if the orangutans’ welfare was affected by the visitor re-introduction phase we predicted there would be an increase in the following measures: (1) use of exhibit areas away from visitors; (2) behavioural measures (hiding, self-directed behaviours, agonistic behaviours, agitated movement, and idiosyncratic object-directed behaviours [head slamming, and fabric tearing]); and (3) physiological measures (faecal consistency and glucocorticoid metabolites) when compared to the lockdown. We also measured changes in activity levels such as foraging and inactivity. We found that orangutan exhibit space use did not change when visitors were reintroduced. In fact, the orangutans hid less when visitors were introduced than during the lockdown. Foraging, inactivity, and other behavioural indicators of stress did not change when visitors were introduced. Similarly, neither faecal consistency nor glucocorticoid metabolites changed across the study phases. Our data show that visitor re-introduction did not negatively affect the welfare of the Toronto Zoo orangutans. However, the presence of keepers was found to affect the behaviour of the orangutans and warrants further study.

As an anthropogenic creation, plastic pollution is a form of human–wildlife interaction and an emerging conservation threat to a growing number of species in both terrestrial and marine environments. Although plastic pollution has spread worldwide and a growing body of literature shows its effects on human health, little is known about its impact on our closest living relatives, nonhuman primates, and their habitats. With over 60% of primate species already under threat of extinction, plastic pollution in their habitats poses a unique problem, exposing them to physical harm, synthetic chemicals, and pathogens through ingestion, entanglement, and oral manipulation. Moreover, through its presence in soil, air, and waterways, plastic pollution leads to environmental degradation and reduces the quality and ecological functionality of primate habitats. This perspective article covers what is known so far about plastic pollution as a conservation threat to nonhuman primates. It is a call for primatologists to address plastic pollution in our research and conservation initiatives. By collecting data on plastic pollution’s presence and assessing its impact on primates and their habitats, we can develop safe protocols and prevention strategies to combat the threat of plastic pollution in the Anthropocene.

The expansion of transportation and service corridors has numerous, well-documented adverse effects on wildlife. However, little research on this topic has been translated into mitigating the effects of habitat fragmentation caused by road development on primates. The establishment of canopy bridges has proven to be an effective conservation intervention. Of the completed primate canopy bridge projects reported in the literature, to our knowledge, all attempt to mitigate the impacts caused by singular, linear infrastructure routes. Here we provide recommendations for the establishment of a network of natural and artificial canopy bridges over roads throughout Langkawi Island, Malaysia, to reduce rates of roadkill and support the movement of primates and other arboreal animals across the island by identifying suitable sites and appropriate tree species to be planted (including Ficus racemosa and Ficus fistulosa), bridge materials and post-installation monitoring. The establishment of this pioneering trans-island canopy bridge network could function as a model to enhance connectivity for arboreal animals in other important wildlife habitat sites in Malaysia and beyond that are affected by fragmentation from linear infrastructure. We have begun discussions with relevant authorities, partners and other pertinent parties, focusing on the initiation of construction of the canopy bridge network in 2024.

Population size and geographical range are the key quantitative criteria used by the IUCN to assess the conservation status of a species. However, such information is often incomplete and inconsistent, even for seemingly abundant species. To assess the population and conservation status of Indian primates, we conducted a systematic review of recent research using the searching, appraisal, synthesis and analysis (SALSA) approach. We reviewed a total of 41 studies on Indian primates conducted during the last 2 decades (2000–2021) for information on various parameters that influence their conservation. We found that 20 out of a total of 26 primate species were evaluated for their population status, and the majority of these studies (71%) showed an overall declining population trend. Remarkably, all but one of the studies conducted exclusively within protected areas revealed declining population trends, whereas trends were more variable for primate populations in non-protected areas. Our data indicate that only 27% (n = 7) of Indian primate species have been surveyed or re-surveyed to assess their population status within the last 5 years. Although threats vary in time and space from species to species, 78% of the studies recorded natural system modifications including habitat loss and fragmentation among the main threats to the survival of Indian primates. Most studies on the population status of Indian primates have either been spatially limited or used outdated methods. We recommend that future studies adopt robust techniques to estimate populations and work across larger geographical scales to develop effective management strategies for the conservation of primates in India.

Capuchin monkeys have rich social relationships and from very young ages they participate in complex interactions with members of their group. Lipsmacking behaviour, which involves at least two individuals in socially mediated interactions, may tell about processes that maintain, accentuate or attenuate emotional exchanges in monkeys. Lipsmacking is a facial expression associated with the establishment and maintenance of affiliative interactions, following under the ‘emotional regulation’ umbrella, which accounts for the ability to manage behavioural responses. We investigated behaviours related to the emitter and to the receiver (infant) of lipsmacking to answer the question of how lipsmacking occurs. In capuchin monkeys, lipsmacking has been previously understood solely as a face-to-face interaction. Our data show that emitters are engaged with infants, looking longer towards their face and seeking eye contact during the display. However, receivers spend most of the time looking away from the emitter and stay in no contact for nearly half of the time. From naturalistic observations of wild infant capuchin monkeys from Brazil we found that lipsmacking is not restricted to mutual gaze, meaning there are other mechanisms in place than previously known. Our results open paths to new insights about the evolution of socio-emotional displays in primates.

Ruffed lemurs (Varecia variegata and Varecia rubra) are categorized as Critically Endangered on the IUCN Red List, and genetic studies are needed for assessing the conservation value of captive populations. Using 280 mitochondrial DNA (mtDNA) D-loop sequences, we studied the genetic diversity and structure of captive ruffed lemurs in Madagascar, Europe and North America. We found 10 new haplotypes: one from the European captive V. rubra population, three from captive V. variegata subcincta (one from Europe and two from Madagascar) and six from other captive V. variegata in Madagascar. We found low mtDNA genetic diversity in the European and North American captive populations of V. variegata. Several founder individuals shared the same mtDNA haplotype and therefore should not be assumed to be unrelated founders when making breeding recommendations. The captive population in Madagascar has high genetic diversity, including haplotypes not yet identified in wild populations. We determined the probable geographical provenance of founders of captive populations by comparison with previous studies; all reported haplotypes from captive ruffed lemurs were identical to or clustered with haplotypes from wild populations located north of the Mangoro River in Madagascar. Effective conservation strategies for wild populations, with potentially unidentified genetic diversity, should still be considered the priority for conserving ruffed lemurs. However, our results illustrate that the captive population in Madagascar has conservation value as a source of potential release stock for reintroduction or reinforcement projects and that cross-regional transfers within the global captive population could increase the genetic diversity and therefore the conservation value of each regional population.

Behavioural and salivary Cortisol responses were measured in hamadryas baboons (Papio hamadryas) (n = 5) undergoing positive reinforcement training (PRT). Compliance was assessed by collecting behavioural data on desirable and undesirable responses during each training session (33-46 training sessions per male). Saliva was collected before implementation of the training programme (3-4 baseline samples per male) and immediately before and ten minutes after a training session (24-53 saliva samples per male). During training, the incidence of leaving the training area, vocalising and threat displays changed across time. Performance of the desired behaviour (holding a target for increasing increments of time) improved for all males during the study period. Concentrations of salivary cortisol were similar for pre-training and post-training collection times, but both were significantly lower than baseline concentrations. The overall decline in undesirable behaviours and the absence of constantly elevated salivary cortisol suggest that PRT had no adverse effects on animal welfare.

A review of the scientific literature gives evidence that transferring previously single-caged adult macaques to permanent compatible pair-housing arrangements (isosexual pairs, adult/infant pairs) is associated with less risk of injury and morbidity than transferring them to permanent group-housing arrangements. Juvenile animals can readily be transferred to permanent group-housing situations without undue risks. Safe pair formation and subsequent pair-housing techniques have been developed for female and male rhesus (Macaca mulatta), stump-tailed (M. arctoides) and pig-tailed macaques (M. nemestrina) as well as for female long-tailed macaques (M. fascicularis). Pair housing does not jeopardize the animals’ physical health but it increases their behavioural health by providing them with an adequate environment to satisfy their need for social contact and social interaction.