The challenge of estimating and monitoring the population size of the endangered peruvian plantcutter (phytotoma raimondii)

Abstract

Population size is a major criterion in evaluating the conservation status of threatened species and for designing management strategies. Therefore, using a distance sampling approach, the number of adult individuals of the endangered Peruvian Plantcutter (Phytotoma raimondii) at the protected area Pómac Forest Historical Sanctuary was estimated in 2016 and contrasted with refined estimates from a survey conducted in 2011. Enough data to model the detection functions were obtained only for adult males because their vocalizations make them more conspicuous than other age classes and females. The estimated density of adult males within polygons of occupancy was 0.075 ind ha-1 (SE = 0.015) in 2011 and 0.057 (0.009) in 2016. Because the estimated number of individuals has remained stable between both sampling periods (z = 1.05, two-tailed p = 0.30), the count data were combined, resulting in an estimated density of 0.064 ind ha-1 (0.008) and a total subpopulation size of 188 adult males (95% CI = 144-237, CV = 0.13). By assuming plausible scenarios of sexual proportions from a male-biased population, in which 70% of adults are males to an even adult sex ratio, the total number of adults at this subpopulation can vary between 269 (95% CI 206-339) and 376 (288-474) individuals. The pooled data from both surveys were also used to estimate the sampling efforts required to achieve multiple levels of precision (CV = 0.10-0.20). In summary, this paper constitutes a baseline of the number of adult Peruvian Plantcutters at one of the last strongholds of the species, providing detailed information for replicability and improvement. The direct implications of the study results to the current knowledge and conservation status of this species are discussed.