Glacier influence on bird assemblages in habitat islands of the high Bolivian Andes

Aim: Climate projections for the upcoming decades predict a significant loss of ice mass particularly critical for glaciers in tropical mountains. In the dry landscapes of the southern Andes (from Southern Peru to Chile), this global trend has strong ecological impacts on high-altitude wetlands that support a unique avifauna for feeding, roosting and nesting. As glacier runoffs are expected to affect the area and the quality of wetland habitats, these changes may potentially affect bird communities. To address this issue, we studied the structural and functional diversity of bird assemblages in glacier-fed high-altitude wetlands (>4500 m). Location: Five valleys of the Cordillera Real, Bolivia. Methods: We surveyed bird communities during dry, wet and intermediate seasons in 40 wetlands (total of 27,720 observations of birds and habitats from 540 transects) showing different degrees of dependence on glacial meltwater. We examined the potential effect of glacier retreat on bird communities through changes in wetland area and environmental quality and heterogeneity. Results: We found strong relationship between wetland area and taxonomic and functional diversity, but not on phylogenetic diversity. Generalized additive models revealed that avian diversity was influenced by wetland's productivity and elevation and maximized at intermediate levels of glacier influence. Multivariate analysis further showed that habitat productivity and humidity, both potentially influenced by future glacial retreat trends, are the main drivers of bird community composition, with the wettest habitats being crucial for aquatic birds and uncommon species. Main conclusions: Glacier retreat may significantly affect bird community diversity and composition through changes in both area and quality of high-altitude wetlands, with a particular concern for aquatic birds.