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

Measuring Gestation Length in the Chimpanzees of Gombe National Park


Evolutionary Anthropology, Duke University

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The chimpanzees (Pan troglodytes schweinfurthii) of Gombe National Park, Tanzania, have been studied since the early 1960s. Since that time, dozens of offspring have been born into the Kasekela community, and researchers have typically assigned conception dates retrospectively following a live birth. Previous estimates of gestation from captive and wild populations have ranged from 224.5 to 231.5 days. However, a review of all the births since the beginning of the study has not been undertaken in 15 years. Using daily records from the long-term database, we examined observations of sexual swellings before each live birth between 1970-2008. Of these, 36 gestations from 18 females were supported by observations complete enough to assign the last day of maximal swelling of the conceptive cycle, which is considered the day of conception. The average gestation length for singletons is 226.5 days (n=33; sd = 8.05) and 201 days (n=3; sd = 2) for twins. Gestation length is normally distributed (n=36; mean = 224.6, Shapiro-Wilk Test W = 0.97, p = 0.5753). Twin gestations are significantly shorter than the singleton gestations (t (11) = -14.33, p < .0001). Because many births are characterized in our long-term data by long gaps between observations of the female during gestation, these analyses can be used to inform estimates of conception date where sightings of sexual swellings are insufficient. There is variation across the sample, even within singleton births (range in gestation length: 214-248 days), and future research will focus on possible drivers of this variation.

Data collection supported by the Jane Goodall Institute. Construction of the longterm database was supported by grants from the NSF (DBS-9021946, SBR-9319909, BCS-0452315, IOS-LTREB-1052693)

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