<b>Un modelo de detección imperfecta para conocer de forma rápida y participativa el estado poblacional de </b><b><i>Atelopus varius</i></b><b> en el territorio indígena Bribri, Costa Rica</b>

A population of the critically endangered frog Atelopus varius is reported for the first time, and its population structure and density are assessed in a participatory manner in the Örkö Bata Nature Reserve. Members of the community in the locality of Salitre were trained to survey and record individuals of A. varius. A 350 m stretch along a stream was surveyed, which was divided into seven 50 m transects. Population density and structure were estimated using the distance sampling method and the Multinomial-Poisson Mixture model. A total of 64 individuals were recorded, with density explained by age. The highest density was for adults with 399.85 individuals/ha, followed by juveniles with 225.21 individuals/ha and finally metamorphs and subadults with 48.32 and 46.08 individuals/ha, respectively. We demonstrated the viability of using imperfect detection models for rapid and participatory assessments of the density and population structure of species with urgent conservation needs, such as A. varius. We suggest monitoring the population at several periods throughout the year and increasing the sample size to reduce uncertainty in the estimates of some age categories (subadults and metamorphs). We also recommend continuing with a participatory approach in order to maintain long-term population monitoring by local people.