Wendy M. Erb

Demography of Simakobu (Simias concolor) and the Impact of Human Disturbance

Asian colobines typically live in small one‐male groups (OMGs) averaging five adult females, but Simias concolor (simakobu or pig‐tailed langur) is considered an exception because mostly adult male–female pairs have been reported. However, based on their phylogenetic position and marked sexual dimorphism, simakobu are also expected to form OMGs with multiple females. The preponderance of small groups could be the result of human disturbance (hunting or habitat disturbance) reducing group size in the recent past. To investigate this possibility, we documented the demography of ten wild simakobu groups from January 2007 until December 2008 at an undisturbed site, the Peleonan Forest, Siberut Island, Indonesia. We assessed the population‐specific size and composition of groups and documented demographic changes due to births, disappearances, and dispersals throughout our 2‐year study. We found OMGs with 3.0 adult females on average in addition to all‐male groups, but no adult male–female pairs. The ratio of 0.5 infants per adult female (and 0.64 births per female‐year in focal groups) suggested that birth rates were similar to those of other Asian colobines. In 5.1 group‐years, we observed six dispersal events and six temporary presences (i.e., less than 3 months’ residency). Both males and females dispersed, and juveniles seemed to disperse more frequently than adults. To assess the impact of human disturbance on simakobu demography, we compiled data for seven additional populations from the literature and compared them using multiple regressions. Adult sex ratio and the number of immatures per group were influenced negatively by hunting and positively by habitat disturbance while reproductive rates were not significantly affected by either variable. These findings suggest that adult male–female pairs may result from hunting pressure reducing group size, and that conservation action to reduce hunting in the Mentawai Islands is needed to ensure the survival of this critically endangered species. Am. J. Primatol. 74:580–590, 2012.

Individual, contextual, and age-related acoustic variation in Simakobu (Simias concolor) loud calls.

Primate loud calls have the potential to encode information about the identity, arousal, age, or physical condition of the caller, even at long distances. In this study, we conducted an analysis of the acoustic features of the loud calls produced by a species of Asian colobine monkey (simakobu, Simias concolor). Adult male simakobu produce loud calls spontaneously and in response to loud sounds and other loud calls, which are audible more than 500 m. Individual differences in calling rates and durations exist, but it is unknown what these differences signal and which other acoustic features vary among individuals. We aimed to describe the structure and usage of calls and to examine acoustic features that vary within and among individuals. We determined the context of 318 loud calls and analyzed 170 loud calls recorded from 10 adult males at an undisturbed site, Pungut, Siberut Island, Indonesia. Most calls (53%) followed the loud call of another male, 31% were spontaneous, and the remaining 16% followed a loud environmental disturbance. The fundamental frequency (F0) decreased while inter-unit intervals (IUI) increased over the course of loud call bouts, possibly indicating caller fatigue. Discriminant function analysis indicated that calls were not well discriminated by context, but spontaneous calls had higher peak frequencies, suggesting a higher level of arousal. Individual calls were distinct and individuals were mainly discriminated by IUI, call duration, and F0. Loud calls of older males had shorter IUI and lower F0, while middle-aged males had the highest peak frequencies. Overall, we found that calls were individually distinct and may provide information about the age, stamina, and arousal of the calling male, and could thus be a way for males and females to assess competitors and mates from long distances.

Mother's little helpers: What we know (and don't know) about cooperative infant care in callitrichines

Since Darwin ( ), scientists have been puzzled by how behaviors that impose fitness costs on helpers while benefiting their competitors could evolve through natural selection. Hamiltons ( ) theory of inclusive fitness provided an explanation by showing how cooperative behaviors could be adaptive if directed at closely related kin. Recent studies, however, have begun to question whether kin selection is sufficient to explain cooperative behavior in some species (Bergmüller, Johnstone, Russell, & Bshary, ). Many researchers have instead emphasized the importance of direct fitness benefits for helpers in the evolution of cooperative breeding systems. Furthermore, individuals can vary in who, when, and how much they help, and the factors that affect this variation are poorly understood (Cockburn, ; Heinsohn, ). Cooperative breeders thus provide excellent models for the study of evolutionary theories of cooperation and conflict (Cant, ).

Nutritional ecology of wild Bornean orangutans (Pongo pygmaeus wurmbii) in a peat swamp habitat: Effects of age, sex, and season

The spatial and temporal variation in food abundance has strong effects on wildlife feeding and nutrition. This variation is exemplified by the peatland forests of Central Kalimantan, which are characterized by unpredictable fruiting fluctuations, relatively low levels of fruit availability, and low fruit periods (<3% of trees fruiting) that can last nearly a year. Challenged by these environments, large, arboreal frugivores like orangutans must periodically rely on non‐preferred, lower‐quality foods to meet their nutritional needs. We examined variation in nutrient intake among age‐sex classes and seasons over a 7‐year period at the Tuanan Orangutan Research Station in Central Kalimantan. We conducted 2,316 full‐day focal follows on 62 habituated orangutans (Pongo pygmaeus wurmbii). We found differences in total energy and macronutrient intake across age‐sex classes, controlling for metabolic body mass. Intake of both total energy and macronutrients varied with fruit availability, and preference of dietary items increased with their nutritional quality. Foraging‐related variables, such as day journey length, travel time, and feeding time, also varied among age‐sex classes and with fruit availability. Our results add to the growing body of literature suggesting that great variation in foraging strategies exists among species, populations, and age‐sex classes and in response to periods of resource scarcity.

Are simakobu (Simias concolor) loud calls energetically costly signals

OBJECTIVES Male vocal displays play an important role in sexual selection in many species. If there are costs or constraints, calls may convey honest information about the caller. We studied the loud calls of male simakobu (Simias concolor), a sexually dimorphic primate that resides in one-male groups, on Siberut Island, Indonesia. MATERIALS AND METHODS We combined behavioral and ecological data with acoustic analysis to determine the influence of energy costs and status on calling effort. Based on all-day follows (n = 107) and loud-call recordings (n = 186), we determined how calling rates and durations varied in relation to short-term (time of day, temperature, travel distance) and long-term (fruit availability, physical condition) measures of energy availability and expenditure. RESULTS We found that males avoided calling at the hottest times of the day, and produced shorter calls at higher temperatures, supporting the hypothesis that calls are influenced by thermoregulation costs. A peak of longer duration calls just before sunrise, however, could not be explained by energy constraints, but we hypothesize that this pattern is related to the fact that dawn calls occur in choruses, motivating males to call longer than their neighbors. Contrary to predictions, calling rates increased with decreasing fruit availability and did not appear to be energetically costly. DISCUSSION We hypothesize that calling rates instead reflect strategies involving feeding and/or mate competition, signaling the motivation, rather than fighting ability, of the caller. Overall, results only weakly support the hypothesis that the timing and duration-but not rate-of simakobu loud calls are influenced by energy costs. Am J Phys Anthropol 161:44-52, 2016.

2011 Annual Meeting of the American Society of Primatologists

A ustin, Texas was alive with excitement on September 16, in part because of the start of the famous Austin City Limits music festival, as well as the onset of desperately needed rain. But perhaps more importantly, the date also marked the start of the 34 Annual Meeting of the American Society of Primatologists. The following three days showcased a great diversity of podium presentations, posters, and symposia demonstrating the innovative and collaborative approach that primatological laboratory and field studies have adopted, with the keynote speakers reminding us how we, as a discipline, have arrived at this point in our history.

IDENTIFICATION AND COMPOSITION OF FEEDING PLANTSPECIES OF SIMAKOBU MONKEYS (Simias concolor) IN NORTHERN SIBERUT, MENTAWAI ARCHIPELAGO

The availability of food resources is one of habitat components that support simakobu conservation. This study was aimed to identify the species and composition of feeding plants and habitat structures of simakobu. Habituation of simakobu was conducted in prior to the study. Afterwards it was performed to collect the data on species and composition of feeding plants of simakobu using ad libitum methods. Determination of the structure and composition of vegetation on simakobu habitat, vegetation analysis was done by establishing plot measuring all long 100 m for 15 plots. Result showed that amount of 116 plant species was eaten by simakobu. Katatairek (Bhesa paniculata), logauna (Knema sumatrana) and ungla (Aporosa symplocoides) were species that its parts were most widely used as food source of simakobu. Young leaves, leaf bud, fl ower and fruit parts of those speciesare eaten by simakobu. This study suggests that the dominant plant species on the simakobu habitat is Logauna (Knema sumatrana).