Alpha and beta bird diversity in humid and semi-humid tropical forests of the sierra de Atoyac, a priority region for conservation of southern Mexico

This study describes the alpha and beta diversity of the avifauna present in the cloud forest and semideciduous forest along an elevational gradient ranging from 600-2,200 m in the sierra de Atoyac, Guerrero. Bird species records were obtained through sightings and vocal identification in 126 linear transects. Alpha diversity among both forests was compared using rarefaction-extrapolation methods, as well as the number of resident species and endemics between altitudinal intervals. Beta diversity for the resident avifauna among forests and altitudinal intervals was compared. Bird species were categorized according to their type of diet, seasonality, endemism, and conservation status. We recorded 206 bird species. The cloud forest had the highest values of taxonomic richness, as well as the highest proportion of endemic birds and at-risk species. The number of species showed an increase in the medium part of the gradient, but not the endemism. Turnover and nestedness values were lowest among vegetation types and increased when altitudinal intervals were compared. The types of diet best represented in both forests were insectivorous and insectivorousfrugivorous. Bird taxonomic richness of the sierra de Atoyac increased by 28%, which highlights the importance to maintain monitoring strategies in highly biodiverse environments of the Mexican tropics.