Colobines are similar in their exploitation of a high percentage of leaf matter. However, this observation obfuscates interesting differences among genera of Southeast Asian colobines in morphology and behavior that may be reflected in the degree to which they rely on mastication or gut volume and gut retention time when ingesting and digesting leaves. We detail the use of a laboratory-based method to measure the mechanical properties of foods selected and processed by 4 captive species of Southeast Asian Colobinae -Pygathrix nemaeus, Pygathrix cinerea, Trachypithecus delacouri, and Trachypithecus laotum hatinhensis-at the Endangered Primate Rescue Center (EPRC), Vietnam. We also detail a field method that quantifies chewing rates and chewing behavior via a consumer-grade video camera and laptop computer. Observations in the captive setting permit a degree of experimental control that is not possible in the wild, and the location of the EPRC in the primates' habitat country permitted us to provide leaves that they encounter and eat in the wild. We collected toughness data with a portable tester designed by Lucas et al. The average toughness of selected leaves does not differ among the taxa, nor does the length of time spent chewing foods. However, there are differences in feeding rate, with Trachypithecus spp. chewing foods twice as fast as Pygathrix spp. Our findings suggest that Trachypithecus spp. emphasize comminution of food by mastication, while Pygathrix spp. emphasize the comminution of leaf matter Int J Primatol (in the stomach. The hypothesis is supported by data on molar size, gut mass, and gut morphology. We provide new insights into dietary variation among primate species and detail methods that are typically conducted only in a laboratory setting. We augment the findings with additional data on activity, feeding rates, and tooth morphology.

Adult males of some primate species are known to positively interact with juveniles. In cases where paternal certainty is high, these behaviors have been largely attributed to the paternal investment hypothesis. Males have also been observed to interact with nonkin juveniles, which has often been explained in terms of mating effort. Here, we examined variation in adult male-juvenile affiliation in semi-free ranging Japanese macaques (<i>Macaca fuscata</i>) at the Oregon National Primate Research Center against possible influencing factors such as age, dominance rank, and female affiliation, and we also tested for fitness benefits. We conducted 154 h of focal observations of 14 adult males from June to September 2018. Males differed significantly in their rate of juvenile-directed affiliation, but not in their fitness in terms of number of offspring. There was a significant positive correlation between rank and age in the group, indicating that, in this group, rank does not conform to the classic inverted-U pattern observed elsewhere in this species. Although there was a significant positive correlation between rank and juvenile-directed affiliation, the highest-ranking male had few offspring and exhibited little juvenile-directed affiliation. These results suggest little to no preliminary support for either the paternal investment or mating effort hypotheses as explanations for juvenile-directed affiliation. This study suggests that there are multiple behavioral strategies for older males that may influence reproductive success.

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.

The home ranges of odd-nosed colobines as reported by a number of studies can vary greatly both within and between taxa. Evaluating Pygathrix, particularly within the context of the odd-nosed colobines, has proven challenging due to the comparable dearth of published data on all three species-Pygathrix nigripes, Pygathrix cinerea, and Pygathrix nemaeus. This dearth has also proven challenging when as-

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