Addressing multiple sources of uncertainty in the estimation of global parrot abundance from roost counts: A case study with the Vinaceous-breasted Parrot (Amazona vinacea)

Abstract

Population size is a key predictor of extinction risk and is critical to listing species in IUCN threat categories. Assessing population size can be particularly difficult for gregarious species, such as parrots—one of the most threatened bird families—whose ecology and behavior generate multiple sources of uncertainty that need to be addressed in monitoring efforts. To improve estimates of abundance for the endangered Vinaceous-breasted Parrot (Amazona vinacea), we combined extensive roost counts over the global range of the species (Argentina, Paraguay, Brazil) with an intensive regional survey designed to address five sources of uncertainty about parrot abundance in western Santa Catarina state (WSC), Brazil, in 2016 and 2017. We estimated abundance at both regional and whole-range scales using N-mixture models of replicated count data, which account for imperfect detection. The regional-scale estimate was 1826 ± 236 and 1896 ± 105 individuals for 2016 and 2017, respectively; global abundance was estimated at 7789 ± 655 and 8483 ± 693 individuals for the same two years. We found no statistical evidence of population change at either scale of the analysis. Although our assessments of abundance and geographic range are larger than those currently reported by the IUCN, we suggest the Vinaceous-breasted Parrot should remain in the ‘Endangered’ IUCN threat category pending further investigation of population trends. We recommend that roost-monitoring programs for parrots consider and address sources of uncertainty through adequate field protocols and statistical analyses, to better inform assessments of population size, trends, and threat status.