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.

The influence of an environmental enrichment feeding device (puzzle feeder), on activity and behaviour patterns of captive orang-utans, gorillas and chimpanzees was studied at London Zoo. General activity levels and behaviours directed towards the feeder increased for all species when the feeder was filled with food Chimpanzees used the feeder significantly more (18% of observation periods) than either gorillas (10%) or orang-utans (9.4%). There was considerable individual variation of puzzle use by individuals within each group and time of day also affected use. In some instances abnormal behaviours were reduced. These results are discussed in relation to the management of captive great apes and it is suggested that the use of puzzle feeders can improve the welfare of these animals.

The presence of human visitors has been shown to affect the behaviour of several different mammalian species in a number of different zoos, but the behavioural changes observed are not always consistent with a simple ‘stressful influence’ explanation. Data for non-primate species are too sparse to draw meaningful conclusions; but for primates, the evidence reviewed in this paper allows several hypotheses to be tested. Neither a social facilitation nor an audience attraction hypothesis can be generally supported by the available studies. However, these studies are consistent with a general stressful influence hypothesis, although the extent of this influence is itself affected by other variables, notably species and housing differences. There is some evidence that chronic exposure to human audiences may lessen this stressful influence in some species; and in certain circumstances (notably where some members of the public throw food) the effect of the audience is almost an enriching one.

Aggression and agonism typically accompany the initial interactions exchanged between unfamiliar primates. As a part of a larger study examining the social function of scrotal colour in vervet monkeys (Cercopithecus aethiops sabaeus), this paper offers experimental data to show how scrotal colour can influence aggression, and how artificial colour treatment can be used as an effective tool for managing aggression. Study animals were 81 vervet monkey pairs composed of 162 similarly-sized, unfamiliar adult males originating from non-adjacent parishes in Barbados. Non-contact and contact aggression were recorded on a continuous basis during 90 minute introductions. The main effects of the Test male scrotal colour, Stimulus male colour, and the interaction of the Test male and Stimulus male colours were not significant predictors of non-contact aggression. The effects of scrotal colouration of the Test male and Stimulus male were not significant predictors of contact aggression either, but there was a significant interaction effect; pairs of males with similar scrotal colour engaged in contact aggression more often than pairs of males differing in colour. Painting the scrotum dark led to more aggression when these males were paired with dark coloured males and less aggression when these males were paired with pale coloured males. These findings suggest a practical and inexpensive means of reducing the likelihood of aggression when introducing new animals. These results may also be applicable for other taxa that have colourful sexual skin, such as mandrills, drills, talapoins, patas monkeys, and many guenon species.

The success of breeding primates in captivity has led to a surplus number of animals in collections. This review examines published journals and key books to investigate the various methods of primate population control. Hormonal, surgical and separation methods are discussed and evaluated with regards to behavioural and welfare implications. Methods of dealing with surplus animals are also reviewed. It is concluded that the successes of contraception methods vary significantly between species, and in some cases not enough is known to conclusively state that one method is preferable to another. The behavioural effects of contraception should be evaluated, as social status and sexual behaviours can be negatively affected by contraception. Non-reversible sterilisation methods, such as castration, should not be used without thorough evaluation due to the behavioural effects on the individual and group as a whole. Overall, the zoo community should share information of successes and failures of contraception in different species, and professional advice should be sought to ensure that the welfare of primates in captivity is not compromised.

The Lower Pleistocene Karnezeika locality, lies in the Peloponnese, southern Greece, and its fauna corresponds to the Middle Villafranchian biochronological unit (MN17). The recovered mammal assemblage includes, among others, a few remains of a large Cercopithecid. Herein, we describe this material, including an upper second molar, a partially preserved proximal radius and, possibly, an upper first incisor. The teeth show advanced stages of wear but retain their typical papionin characters, such as a strong lingual cleft and four bilophodont cusps in the molar. The general morphology and wear pattern of the teeth rules out the possibility that the remains belong to the genus Theropithecus, while the general size of the corresponding material excludes the possibility of a Macaca representative as well. On the contrary, the studied material better fits the size range of Paradolichopithecus. Even though this genus is likely represented in the Villafranchian of Europe by a single species, Par. arvernensis, the scarcity of the studied material imposes reservations and thus the Karnezeika papionin is referred at the moment to cf. Paradolichopithecus sp. As in the rest of Europe, the Paradolichopithecus record is rare in Greece, having been found in only two localities, Vatera and Dafnero. Despite its scarcity, the new material from Karnezeika indicates a wide distribution of this important taxon in the Greek peninsula.