Silky sifaka (Propithecus candidus) use sleep sites for thermoregulation, food access and predator avoidance

Primate sleeping site selection is influenced by multiple ecological factors including predation avoidance, thermoregulation, and food access. To test these hypotheses, we studied the sleeping trees used by a group of wild silky sifakas (Propithecus candidus) in Marojejy National Park, Madagascar. During this ten-month study, the group slept in 828 sleeping trees from approximately 35 genera. In support of thermoregulation, generalised linear models revealed that as temperature decreased, the number of individuals sleeping together significantly increased and they slept at further distances from the trunk. As rainfall increased, sleep site height significantly increased. Weinmannia was the most frequented tree genus, despite low abundance, accounting for 29% of all sleeping trees. In support of food access, 94.8% of sleeping trees were food trees. Weinmannia is among the most highly preferred food trees. The group slept at a mean height of 16.0 m near the top of tall trees which averaged 19.5 m. Sleep trees were significantly taller than trees in botanical plots within the sifaka’s home range. They never slept in the same trees on consecutive nights, and sleeping heights were significantly higher than daytime heights which is consistent with predation avoidance. Social sleeping in groups of two or three individuals (62.9%) was more common than solitary sleeping (37.1%). At such heights, huddling may increase vigilance and lessen the risk of predation by the fossa (Cryptoprocta ferox) while also reducing heat loss. These patterns suggest that silky sifaka sleep site choice is influenced by thermoregulation and food access in addition to predation avoidance. We suggest that understanding sleep site use can assist in conservation of species like silky sifakas by enabling researchers to find new groups, protect habitats with key tree species, and inform reforestation efforts.

Colour preferences in relation to diet in chimpanzees (Pan troglodytes), gorillas (Gorilla gorilla), and mandrills (Mandrillus sphinx)

Although trichromatic color vision has been extensively studied as it grants significant advantages for Old World primates, it is unknown which selective pressures were behind trait’s evolution. The leading hypothesis would be that colour vision arose as a foraging adaptation because it allowed individuals to spot food more efficiently. To test this, we exposed three chimpanzees (Pan troglodytes), five gorillas (Gorilla gorilla) and three mandrills (Mandrillus sphinx) to colour cardboard plates to assess if colours related to diet were the most preferred. Experimental setting was divided in two phases. During the first one, animals were provided with colour cardboard plates of only one colour per data collection session. The order of colour presentation was randomly determined: white, black, yellow, green and red. In phase two, primates were simultaneously provided with cardboard plates of all colours. Behavioural interactions with plates were measured using a one-zero group focal sampling (10 s sampling intervals and 20 m observation periods). Results showed that when animals were exposed to only one colour at a time, they exhibited different colour preferences depending on the species considered. Chimpanzees preferred red and yellow, the colours linked to fruits, while gorillas selected red and white. Mandrills exhibited fewer differences between colours preference, being red the most selected. Furthermore, when all colours were simultaneously provided, individuals chose colours related to diet over black and white. Although there were clear individual differences, our results support that trichromatic color vision is an advantage in detecting and selecting red items. In the wild, it could be important in the detection of reddish fruits and leaves.

Primate selfies and anthropozoonotic diseases: lack of rule compliance and poor risk perception threatens orangutans.

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.

Spondyloarthritis in Taihangshan Macaques (Macaca mulatta tcheliensis)

The rhesus macaque (<i>Macaca mulatta</i>) is the most widely distributed nonhuman primate species, and captive populations play an important role in biomedical research due to close phylogenetic and physiological similarity to human beings. However, to our best knowledge, the spondyloarthritis (SpA) in rhesus macaques has been exclusively reported in captive or semicaptive populations rather than wild counterparts. In the present study, we report 2 cases of SpA observed in Taihangshan macaques (<i>Macaca mulatta tcheliensis</i>) inhabiting the Taihangshan Macaque National Nature Reserve, Henan Province, China. Among these 2 cases, one can be diagnosed as ankylosing spondylitis (AS) following accepted medical criteria, and another case showed evident fusion at the pubic symphysis which could be specific to rhesus macaque AS. We discuss the potential causes leading directly or indirectly to the development of SpA.

Group Composition and Social Structure of Red-Shanked Doucs (Pygathrix nemaeus) at Son Tra Nature Reserve, Vietnam

Multilevel societies, consisting of multiple one-male multi-female units, are relatively rare among primates, but are more widespread in the odd-nosed colobines than other taxa. Multilevel societies are found particularly in snub-nosed monkeys (<i>Rhinopithecus</i>)<i></i>and have been debated in studies of proboscis monkeys (<i>Proboscis</i>). While it has been suggested that douc langurs (<i>Pygathrix</i>) may also form multilevel societies, the limited data available make the details of their social organization unclear. We aimed to establish a more comprehensive picture of the social organization of red-shanked doucs (<i>Pygathrix nemaeus</i>) and to address the question of whether this species forms multilevel societies, specifically collections of multiple distinct one-male units hereafter termed “bands.” We collected 259 h of behavioral data at Son Tra Nature Reserve in Vietnam from February 2010 to May 2011. The mean band size was approximately 18 individuals. Bands were comprised of approximately 2.7 units, and each unit contained approximately 6.5 individuals. Units had an average sex ratio of 1.0:1.6. We observed fission and fusion behaviors which were not correlated with phenological or weather measures. Activity budget data showed that fission and fusion behaviors between units were positively correlated with activity. Both vocalizations and vigilance increased when units engaged in fission. Based on this evidence, <i>P. nemaeus</i> at Son Tra Nature Reserve appear to engage in daily fission-fusion activity which does not vary between seasons. Additionally, our data suggest that these primates may form multilevel societies made up of distinct units. However, future data including proximity pattern analyses are necessary for confirmation.

Characterization of Cycling in a Hoolock Gibbon (Hoolock leuconedys)

Here we examine the patterns of reproductive hormones (progesterone and estrone-3 glucuronide, or E1G) in one female hoolock gibbon (<i>Hoolock leuconedys</i>) housed at the Gibbon Conservation Center, throughout the maturation period. Three hundred forty-five fecal samples were collected from the individual over a 5-year period (2012–2017) beginning at the age of 6 years and ending at the age of 11. The average measured progesterone concentration increased from 19.572 ± 1.706 ng/g feces in 2012 to 107.922 ± 12.094 ng/g feces in 2016/17 (<i>p</i> &#x3c; 0.00001). The average measured estrogen value increased from 1.234 ± 0.063 ng/g feces in 2012 to 2.783 ± 0.274 ng/g feces in 2016/17 (<i>p</i> &#x3c; 0.00001). This was accompanied by the emergence of a clear hormonal cycling pattern in the 2016/17 samples that was absent in all earlier samples. These data are consistent with the known sexual maturation period for other gibbon species, which typically occurs between the ages of 6 and 8 but shows some variation. To our knowledge, this is the first hormonal study and first data on cycle length for a hoolock gibbon.

Comparative Stress Response of Black and Gold Howler Monkey (Alouatta caraya) in Urban and Rural Environments of Northern Argentina

The expansion of human populations associated with urbanization results in extensive modification of natural habitats. While many species cannot persist in these highly modified environments, some species adopt new strategies, which contribute to their survival. Several primate species have persisted in altered habitats, including members of the genus <i>Alouatta</i>. To improve our understanding of this interplay, we compared glucocorticoid (GCC) levels in male and female black and gold howler monkeys (<i>Alouatta caraya</i>) in urban and rural areas in northeastern Argentina. Fecal samples (<i>n</i> = 60) were collected from adults and hormone extracts were analyzed by enzyme immunoassays (EIA). Monkeys living in urban areas (females: 109.15 ± 18.83; males: 106.15 ± 10.48) had lower GCC<i></i>levels than monkeys living in rural areas (females: 152.01 ± 19.50; males:139,82 ± 10.85). Interestingly, males living in urban areas had lower GCC levels compared to those living in rural areas, whereas no differences were observed in GCC levels between females living in urban and rural areas. While these results suggest that urban areas may provide a release from intergroup competition for male howler monkeys, future work is needed to better understand the dynamics of this association to best inform management and conservation of this vulnerable species.

Possible Infanticidal Event of an Aye-Aye (Daubentonia madagascariensis) in Torotorofotsy, Madagascar

Infanticide occurs in an array of mammalian species, especially primates. Most infanticidal events occur in polygynous societies, though they sometimes happen in nongregarious populations. We witnessed a possible infanticidal event of a 3-month-old male aye-aye, a species that exhibits a dispersed multimale social system, in Torotorofotsy, Madagascar. Though firsthand killing of the infant was not observed, physical injuries to the infant, vocalizations of the adult female, and her subsequent chase of the adult male aye-aye strongly indicates infanticide. If true, this would be the first recorded incident of an infanticidal event in a noyau primate. The evidence for three different explanations of infanticide is evaluated.