The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)

When animals disappear: An examination of factors influencing which individuals disappeared from a wild population of lemurs


Anthropology, University of Texas at Austin

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In the course of research on wild primates, individual animals inevitably disappear from study populations. The reasons for these disappearances are often difficult to determine but may include dispersal or death. Here I analyze long-term data to determine which factors increased the likelihood that an individual disappeared in a Verreaux’s sifaka (Propithecus verreauxi) population from Kirindy Mitea National Park of western Madagascar. Since the beginning of the study in 2006, 69 individuals in 9 social groups have been marked with collars. Individuals in 5 social groups have been censused monthly, and 4 groups have been the focus of behavioral observations. In an analysis of these individuals representing 233 lemur years, 38 individuals disappeared, including 5 confirmed deaths. Disappearances occurred at a rate of 0.16/lemur year, much lower than at the nearby Kirindy Forest sifaka population. In a mixed effects logistic regression model, group size and sex were significant predictors of whether an individual disappeared from the study population but age was not. Nearly half (47%) of the disappearances were infants and juveniles, who were unlikely to have dispersed. Infant mortality (32%) was unrelated to mother’s rank and substantially lower than the Beza-Mahafaly sifaka population but similar to the Kirindy Forest population. These differences between sifaka populations are probably the result of variation in habitat and population density. These results showing an effect of group size and sex but not rank on the probability of disappearance fit expectations for folivorous primates with male-biased dispersal according to socioecological models.

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