Abstract
Riparian vegetation acts as a transition zone between aquatic and terrestrial ecosystems and plays an important role in ecosystem functioning. In this study, we aimed to assess the response of bird communities to the ecological degradation of stream ecosystems by urbanisation, and assess their potential as ecological indicators of lotic ecosystems beyond aquatic macroinvertebrate communities. For that purpose, we selected 15 urban streams (Coimbra, Portugal), covering an urbanisation gradient. We performed a bird survey to characterise existing communities in the riparian areas and stream channels. In addition, we characterised the aquatic macroinvertebrate communities, a well-established biological quality element of rivers, the physicochemical quality of the water, the hydromorphological conditions and riparian vegetation structure. The bird assemblage composition was strongly influenced by riparian vegetation cover, habitat quality and hydromorphological alterations. The number of insectivorous bird species was positively associated with tree and shrub cover, and negatively correlated with riparian degradation, while those of granivorous birds increased in more urbanised areas and degraded ecosystems. Multidimensional patterns of bird assemblages in the urban streams could be discriminated into two groups, which were related to either better or poorer environmental conditions. There was only a partial correspondence of these patterns with the biological quality classification of streams given by the macroinvertebrate data. A biological-environmental correlation analysis further highlighted that riparian vegetation structure and composition, along with hydromorphological quality and water quality, explained the composition of both bird and invertebrate assemblages, although the former were more relevant for the bird communities. We conclude that bird distribution may provide valuable information on riparian integrity and may serve as a complementary tool for the evaluation of the ecological condition of urban streams.