Primate chemical communication remains underappreciated, as primates are considered to rely on other sensory modalities. However, various lines of evidence suggest that olfaction plays an important role in primate societies, including the conspicuous scent-marking behavior of many strepsirrhines and callitrichines. Although lemurs typically show scent-marking, little is known about this behavior in red-ruffed lemurs (Varecia variegata rubra). We combined behavioral observations and semiochemistry analyses to improve our understanding of scent-marking in two captive troops housed at Dudley and Twycross zoos (UK). We collected olfactory behavioral observations by focusing on two family troops (N = 7) for 132 hr. We investigated the volatile compounds of ano-genital scent-marks using solid-phase microextraction and gas chromatography-mass spectrometry and compared volatile chemical profiles with features of the signaller. Males scent-marked most frequently and predominantly in specific meaningful areas of the enclosure, while within females the occurrence of scent-marking was related to their age. We found behavioral sexual dimorphism, with male predominantly depositing secretions via neck and mandible glands and females via ano-genital glands. We identified a total of 32 volatile components of ano-genital gland secretion, including compounds that have already been found in other mammals as sex pheromones and cues to fitness, in ano-genital scent-marks spontaneously left on filter paper by adult females. Our findings suggest that red-ruffed lemurs might use scent-marking to convey information about sex and female age, with male neckmarking behavior playing defensive territorial functions and ano-genital marking related to socio-sexual communication. K E Y W O R D S communication, gas chromatography-mass spectrometry, olfaction, signaling, Varecia variegata rubra

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Forest structure, defined as the three-dimensional vertical and horizontal distribution of canopy vegetation, has great influence on the distribution patterns and abundance of forest primates. The complexity of this structural canopy produces a diverse range of microhabitats and distinct ecological niches, allowing ecologically similar species to co-exist. Degradation of forests through anthropogenic factors significantly alters forest structure, and arboreal species such as gibbons are particularly vulnerable to these changes due to their reliance on canopy for survival. We investigated how forest structural variables influenced the density of two sympatric gibbon species (siamangs Symphalangus syndactylus and lar gibbons Hylobates lar) in Sikundur, a historically disturbed tropical lowland forest in north Sumatra. We used auditory sampling to establish group density in 10 locations and assessed structural characteristics of forest within 4-6 vegetation plots in each location. Lar gibbon group densities were 0.53-3.10 groups/km2 and siamang group densities were lower, with 0.0-1.0 groups/km2. The densities of both species were positively influenced by median height of first bole and the percentage of canopy connectivity. Lar gibbon group density was positively related to large (DBH 30-100 cm), tall (20-25 m) trees with a large crown area (100-300m2), while siamang group density showed no significant relationships with these variables. These findings show canopy connectivity and height to first bole are significant structural variables for the continued presence of

Our understanding of the transmission of anthropozoonotic diseases between humans and nonhuman primates, particularly great apes due to their close genetic relationship with humans, highlights a serious potential threat to the survival of these species. This is particularly the case at tourism sites where risk of disease transmission is increased. We focus on the interaction between tourists and the Critically Endangered Sumatran orangutan (Pongo abelii) at Bukit Lawang in the Gunung Leuser National Park, Indonesia, before and after the park was closed due to the threat of Covid-19 in April 2020. Through analysis of posts on Instagram we determine the extent of compliance by visitors with the rule to keep a minimum distance of 10 meters from orangutans and assess the positional behaviours of the orangutans. Of the 2,229 photographs we assessed between November 2019 and July 2020, 279 depicted one or more orangutans. Forty-two of these contained both a human and an orangutan, and of these all showed inappropriate behaviours (direct contact, feeding orangutans, close proximity <5m) providing direct evidence of noncompliance with the 10m distance rule. Most of these photographs additionally showed orangutans performing abnormal positional behaviours such as being low to or on the ground rather than their natural high position in the canopy; being near the ground and in close proximity to humans increases the risk of anthropozoonotic disease transmission. As expected, we found a significant decrease in number of photographs that were posted following the closure, and a decrease in the proportion of photographs that showed orangutans or tourists feeding orangutans. Tourists do not seem to perceive that they pose risks to the orangutans and therefore increased awareness, education and enforcement of rules by all stakeholders, tourism bodies and government officials need to be actioned in order to safeguard this important population, which is crucial to the future survival of the Sumatran orangutan.