Anthropological Institute and MuseumUniversity of ZurichZurichSwitzerland

Anthropological Institute and MuseumUniversity of ZurichZurichSwitzerland

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van de Waal E.,Anthropological Institute and MuseumUniversity of ZurichZurichSwitzerland | van Schaik C.P.,Anthropological Institute and MuseumUniversity of ZurichZurichSwitzerland
American Journal of Primatology | Year: 2017

Controlled laboratory experiments have delivered extensive and compelling evidence for the diffusion and maintenance of socially learned behavior in primates and other animals. Such evidence is rarer in the wild, but we show that a behavior seeded in a majority of individuals within vervet monkey (Chlorocebus pygerythus) groups may be sustained across several years. Here, we report results of two natural fission events in such groups that offer novel evidence of the resilience of socially transmitted group norms of behavior. Before fission, high ranked females exhibited an almost exclusive adherence to a group preference among two food options, originally introduced through a distasteful additive in one option, but no longer present in repeated later tests. Because of rank-dependent competition, low-ranked females ate more of the formerly distasteful food and so discovered it was now as palatable as the alternative. Despite this experience, low ranked females who formed the splinter groups then expressed a 100% bias for the preferred option of their original parent group, revealing these preferences to be resilient. We interpret this effect as conformity to either the preferences of high rankers or of a majority in the parent group, or both. However, given fissioned individuals' familiarity with their habitat and experimental options, we question the adequacy of the informational function usually ascribed to conformity and discuss alternatives under a concept of "social conformity". © 2017 Wiley Periodicals, Inc.


Ashbury A.M.,Anthropological Institute and MuseumUniversity of ZurichZurichSwitzerland | Dunkel L.P.,Anthropological Institute and MuseumUniversity of ZurichZurichSwitzerland | Spillmann B.,Anthropological Institute and MuseumUniversity of ZurichZurichSwitzerland | Atmoko S.S.U.,Fakultas BiologiUniversitas NasionalJakartaIndonesia | And 2 more authors.
American Journal of Primatology | Year: 2015

Orangutans (genus Pongo) are the largest arboreal mammals, but Bornean orangutans (P. pygmaeus spp.) also spend time on the ground. Here, we investigate ground use among orangutans using 32,000hr of direct focal animal observations from a well-habituated wild population of Bornean orangutans (P. p. wurmbii) living in a closed-canopy swamp forest at Tuanan, Central Kalimantan, Indonesia. Ground use did not change with increasing observation time of well-habituated individuals, suggesting it was not an artifact of observer presence. Flanged males spent the most time on the ground (ca. 5% of active time), weaned immatures the least (around 1%). Females and immatures descended mainly to feed, especially on termites, whereas flanged males traveled more while on the ground. Flanged males may travel more inconspicuously, and perhaps also faster, when moving on the ground. In addition, orangutans engaged in ground-specific behavior, including drinking from and bathing in swamp pools. Supplementary records from 20 ground-level camera traps, totaling 3986 trap days, confirmed the observed age-sex biases in ground use at Tuanan. We conclude that ground use is a natural part of the Bornean orangutan behavioral repertoire, however it remains unclear to what extent food scarcity and canopy structure explain population differences in ground use. © 2015 Wiley Periodicals, Inc.

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