Using Dung to Estimate Gorilla Density: Modeling Dung Production Rate |
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Authors: | Angelique F Todd Hjalmar S Kuehl Chloé Cipolletta Peter D Walsh |
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Institution: | (1) Department of Primatology, Max-Planck-Institute for Evolutionary Anthropology, 04103 Leipzig, Germany;(2) World Wildlife Fund, Dzanga-Sangha Project, BP 1053, Bangui, Central African Republic |
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Abstract: | There is an urgent need for information on western gorilla population sizes and distribution to improve present and plan future
conservation actions. Researchers traditionally have estimated gorilla densities on the basis of nest counts despite demonstrated
variation in nest production and decay rates. The variation may lead to large biases in estimates of gorilla abundance. We
investigated the use of an alternate index of gorilla abundance, via defecation data collected from habituated gorillas at
Bai Hokou, Central African Republic. Our sample of 274/370 defecation events/dung piles produced a production rate of ca. 5 dung piles/d: comparable to previous estimates based on much smaller sample sizes. Heuristic models that failed to account
for imperfect dung pile detection produced a lower defecation rate estimate than that of a maximum likelihood model that explicitly
modeled detection probability. Generalized linear modeling (GLM) showed that dung pile production rate was strongly linked
to rainfall, suggesting that failure to correct for seasonal variation in dung pile production rates could lead to substantial
biases in gorilla abundance estimates. In our study, failing to distinguish between the number of defecation events and the
number of dung piles produced would lead to a ca. 31% overestimate of true gorilla numbers. The use of dung as an index of gorilla abundance shows potential, but more fieldwork
and modeling on seasonal variation in dung production rates is required. |
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Keywords: | dung gorilla density model survey |
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