Can birds help monitor the ecological health of urban streams?
A study recently published in the scientific journal Aquatic Sciences shows that bird community composition in urban streams is strongly linked to riparian vegetation cover, habitat quality and the degree of hydromorphological alteration of watercourses. Researchers from MARE|ARNET at the University of Coimbra and the University of Évora surveyed 15 urban streams in Coimbra spanning a gradient of urbanisation.
Between March and May 2022, the team carried out bird censuses and sampled benthic macroinvertebrates at the same 15 sites, alongside data on water physicochemical quality, hydromorphological conditions, and the structure and composition of riparian vegetation. In total, 265 bird individuals from 29 species were recorded. Blackbirds, blackcaps, serins and house sparrows were the most abundant species, while the kingfisher was the only piscivorous species detected.
River and stream monitoring typically relies on indicators based on aquatic organisms, such as fish, invertebrates and plants, to assess and restore the ecological quality of freshwater systems. However, these indices only capture the influence of riparian vegetation indirectly. Here, the authors reasoned that organisms living directly in these riparian zones, such as birds, could be more directly affected by vegetation degradation along riverbanks.
The results show that insectivorous species richness was positively associated with tree and shrub cover and negatively associated with riparian degradation. Granivorous bird abundance, meanwhile, increased in more urbanised and more degraded ecosystems. The stream with the poorest biological quality and lowest bird richness had an exposed channel, little to no riparian vegetation, and intense human disturbance, while the stream with the best water quality had a dense canopy shading the channel, despite only moderate total vegetation cover.
The patterns observed in bird communities corresponded only partially to the biological quality classification of streams based on macroinvertebrate data. Riparian vegetation structure and composition, together with hydromorphological and water quality, explained the composition of both communities, but proved more determinant for birds than for macroinvertebrates.
The authors conclude that birds could serve as a complementary ecological indicator, rather than a substitute, for existing macroinvertebrate-based assessment methods, by providing information on riparian vegetation integrity that these methods do not directly capture. To fully realise this potential, the researchers call for the development of standardised bird-based indices calibrated for different stream types.
The study was carried out by MARE|ARNET researchers Jorge M. Santos, Maria João Feio, Ana R. Calapez, Sónia R. Q. Serra, Andreína Zerega, Zara Teixeira and Jaime A. Ramos, from the University of Coimbra, the University of Évora, and the Institute for Systems Engineering and Computers at the University of Coimbra.
Text: Patrícia Chaves