A Population Estimate of Chimpanzees (pan Troglodytes Schweinfurthii) in the Ugalla Region Using Standard and Spatially Explicit Genetic Capture-Recapture Methods.

Population parameters such as size, density, and distribution of a species across a landscape are important metrics that inform conservation science and are key to management strategies. In this study, we used genetic capture-recapture methods to estimate the population size and density of the little-studied chimpanzees in the Ugalla region of western Tanzania. From 237 fecal samples collected non-invasively over a 10-month period, we identified a minimum of 113 individuals. Based on the two-innate rate method (TIRM) modeled in the software capwire, we obtained a maximum-likelihood estimate of 322 (CI 227-373) individuals over the 624 km(2) area surveyed. Using a spatially explicit capture-recapture (SECR) method, we estimated a population density of 0.25 (CI 0.16-0.38) individuals/km(2) . Observations of nests and search effort data revealed areas of more intense usage. The findings of this study are an important step in the characterization of the Ugalla chimpanzees, and substantially improve our understanding of the number of chimpanzees that occupy this savanna-woodland region at the easternmost extent of the geographic range of this endangered subspecies.