Evaluating line transect efficiency for estimating vicuña (Vicugna vicugna) population density and habitat use in the Apolobamba National Natural Integrated Management Area, Bolivia

Vicuñas ( Vicugna vicugna ) are sustainably managed in Bolivia as a wild species with highly valuable wool. As part of a community management model, over the last two decades indigenous communities have organized censuses of wild vicuña. In order to validate these community censuses, we estimated vicuña population density and abundance in the Apolobamba National Natural Integrated Management Area in the northwestern Bolivian Andes using a line transect distance sampling approach. We placed 54 transects across 690 km 2 covering most of the vicuña distribution within Apolobamba, with transects conducted on motorcycles on the flatter Andean plain and on foot in the adjacent hills. Using a Multiple Covariate Distance Sampling (MCDS) approach and based on 252 transect encounters the vicuña population density was estimated at 12.53 individuals/km 2 (95% CI 9.51 – 15.07) overall with a half-normal model. A complementary occupancy sampling analysis of the survey data indicated that vicuña occupancy was higher as distance to peat bog increased and vicuña detectability was greater when line transects were conducted on foot. Our population estimate for the area where local communities and park guards traditionally count vicuña was 12,527 animals (95% CI 10,614–––13,815). The community census conducted immediately before our survey counted 11,978 animals. This parity in results for the two methodologies is important as the community census methodology is widely applied across Bolivia to evaluate wild vicuna populations under community management. Our results validate the community census methodology as an accurate and participative methodology for monitoring wild vicuña populations into the future.