Effects of a large-scale bioretention installation on the species composition of an urban bird community as determined by passive acoustic monitoring.

As urbanization accelerates worldwide, municipalities are attempting to construct new green spaces within their borders. The perceived ecological value of these places is frequently tied to their ability to attract urban wildlife, such as birds, which can easily be observed and enjoyed. As one strategy, stormwater is now frequently managed with green infrastructure: planted areas that retain and treat stormwater rather than merely directing it to surface waters. While these practices have the potential to provide habitat for urban wildlife, the ecological effects of these systems are largely unknown. To assess whether one green infrastructure project increases habitat value, we used passive acoustic monitoring to survey urban bird communities in and near a large green infrastructure project in Columbus, Ohio (USA). Bird communities near bioretention cells (rain gardens) were compared to those at nearby lawns and remnant or restored natural areas. We found that recently installed bioretention cells tended to support more omnivores, lower-canopy foraging species, and species from a higher diversity of feeding guilds than did nearby lawn control sites. We were unable to detect effects of nearby bioretention installations on bird species richness at other sites. The observed differences in species richness were fairly small, and we urge caution when anticipating the habitat value of bioretention cells, at least for bird species. However, the results that we observed suggest that bioretention cells could have a more positive impact on bird communities in different contexts or using different design strategies. The bioretention cells surveyed in this study were small and only planted in grasses and forbs, potentially limiting their ability to offer complex habitat. They were also relatively young, and future work is needed to determine their long-term effect on avian communities and biodiversity of other taxa.