Preliminary assessment of group composition and activity pattern of the critically endangered Bornean Banded Langur Presbytischrysomelaschrysomelas in Tanjung Datu National Park

The Bornean banded langur (Presbytischrysomelaschrysomelas) is critically endangered species primarily found in Sarawak, Malaysia. Albeit this species is in peril, the ecology knowledge of this endemic species of Borneo is still scarce. Thus, a rapid survey employing total count and scan sampling method was conducted between July to August 2023 at Tanjung Datu National Park (TDNP), Sarawak to observe the social interaction of species with the environment. The behaviour of langur was recorded by employing scanning sampling method at 10 minutes intervals. This study sought to provide preliminary data on behavioural ecology of the Bornean banded langur within the national park. During the survey, three groups (consisting two to seven individuals) and a solitary male Bornean banded langur were recorded. The langurs were observed in both dipterocarp forests and coastal forests within the park. The daily activities of the Bornean banded langurs in TDNP were predominantly resting (31%), moving (29%), feeding (26%), vocalizing (14%), but not engaging in other social activities such as grooming, playing and mating. Knowing the behavioural ecological status as well as understanding ecology by identifying the activity pattern of langur is essential to government authorities and pertinent stakeholders to implement conservation strategies for the Bornean banded langur and their habitats.

Forelimb morphology and substrate use in extant Cercopithecidae and the fossil primate community of the Hadar sequence, Ethiopia

It is suggested that joint architecture of the extant cercopithecid forelimb differentiates terrestrial from arboreal quadrupedal species. Linear dimensions of forelimb joint morphology have also been used to assign fossil species to locomotor categories. However, many primates use a mix of terrestrial and arboreal behaviors, which can be problematic when developing models of behavior reconstruction using morphological variation. The current study uses multivariate analyses to identify morphology related to substrate use in primates, including determination of semiterrestriality. Measurements collected from distal humeri and proximal ulnae of 49 extant cercopithecid primate species were selected based on studies indicating that they could individually predict substrate use. Analyses including one-way analysis of variance, principal components, and discriminant functions were conducted to assess their ability to differentiate between arboreal and terrestrial substrate use. The functions created in these analyses are then applied to data from fossil specimens from the Hadar sequence, Ethiopia, sampling both the Hadar and overlying Busidima Formations, to retrodict possible substrate behavior of fossil monkeys at Hadar through time. As this study is designed to identify function and behavior rather than phylogeny, the taxonomic assignment of the fossil specimens is sometimes uncertain, but substrate behavior can still be inferred. Results suggest that substrate use, including semiterrestrial behavior, in extant and extinct primates can be inferred successfully from multivariate analyses based on joint morphology of the monkey elbow. This study reveals that the ecological distribution of primarily terrestrial fossil primate species of the Hadar sequence is comparable to modern-day communities in habitats similar to those reconstructed for the Hadar members.

Group Composition and Monandry in Grizzled Langurs, Presbytis comata, on Java

Grizzled langurs, Presbytis comata, a largely sexually monomorphic species, are reported to occur in populations where either the majority of groups comprise 1 adult male with 1 adult female, or where groups comprise 1 adult male with multiple females. As such, they may have a monandrous mating system. I investigated whether 1-male/1-female groups indeed form a significant part of the species' social system, and whether habitat variation (forest fragment size, distance to the forest edge, altitude) affects social organization. I found the species from sea level to 2,565 m above sea level in groups from 1 to 13 individuals. I recorded mostly 1-male/multifemale groups with offspring or, alternatively, all-male groups. Two out of 55 groups comprised 1-male/1-female groups with offspring. Group size was negatively correlated with altitude and forest fragment size, and positively correlated with increasing distance from the forest edge. Altitudinal variation in group sizes was driven mainly by fewer adult females being present in groups at higher elevations; the number of adult males (almost invariably 1), subadults, juveniles, and infants, as well as the infant/adult female ratio, showed little altitudinal variation. One-male/1-female groups have been recorded repeatedly over a 25-year period in a high-altitude population on Mt. Patuha, West Java, but even here, on average, three fifths of the groups comprise 1 adult male with multiple females. At high-altitude sites, P. comata may indeed have a monandrous mating system, but at lower elevations it seems similar to that of other Presbytis langurs.