Andean bird responses to human disturbances along an elevational gradient

• We explored variation in bird assemblages with different disturbances in the Andes.
• Low to moderate disturbances occurring across elevations were considered.
• Species richness decreased with both elevation and human disturbances.
• Elevation was the main factor explaining species composition.
• Different disturbances resulted in different assemblages at similar elevations.

Understanding patterns of species diversity along environmental gradients is essential to the study of biodiversity. Numerous studies have found variation in species richness and composition of bird communities along elevational gradients, and several others described bird diversity changes following anthropogenic disturbances. Surprisingly, few studies have attempted to disentangle their separate effects on bird assemblages. Here, we explored variation in bird species richness and composition at different levels and types of disturbance along a 4000-m elevational range in the tropical Andes. Bird counts and disturbance measurements were conducted at 85 points distributed along the gradient within Cotapata National Park, Bolivia. Disturbances accounted for in our study correspond to the often overlooked ‘moderate’ levels of disturbance that occur in the Tropical Andes. Diversity patterns were described and compared with GLM models (for species richness) and CCA models (for species composition). We found that bird communities were structured by elevation and disturbance. Species richness decreased with both elevation and habitat openness. Anthropogenic disturbances also modified community composition within the same elevational ranges. We conclude that, whereas elevation remained the most important variable explaining bird species composition, disturbance explained species richness patterns to a higher extent.