Breeding bird assemblages in riparian galleries of the Guadiana River basin (Portugal): the effect of spatial structure and habitat variables

Abstract

AbstractHabitat structure is a major determinant of bird community composition and a link between riparian vegetation and bird communities in riparian zones, suggesting that changes in bird community composition can be predicted from changes in habitats. Our study aimed to identify the relationships between the structure of breeding bird communities and environmental drivers, using fine‐resolution habitat measurements. We examined two bird assemblages (Passerines, P; and Aquatic/Riparian species, AR) and their spatial structure and relationships to environmental river variables in riparian galleries in southern Portugal. The study was conducted on the ca. 230 km of riparian corridors located in the flooded area of the Alqueva reservoir, before closure of the dam. We used data from 134 10‐min point counts. Using variation partitioning, we determined the independent and joint effects of river edge, river bed, and spatial variables on our selected bird assemblages. The variation in bird assemblages captured was 27.5% for P and 55.3% for AR. The explanatory variables that were highlighted as important predictors for both bird groups were variables that reflected the complexity of the riparian gallery vegetation: rivers with high vegetation cover of riparian species, and riverbeds and riversides dominated by rock and scarce emergent rooted vegetation. Most of the explained variation was related to environmental variables: river‐edge, river‐bed, and their joint effect. Riparian areas can be considered a specific habitat and the variables analyzed are habitat descriptors at a fine scale, so that we believe that the species–environment relationships revealed in this study could be good indicators of the wealth of riparian ecosystems in Mediterranean rivers.