Morgan, M. C. | bioRxiv Science

bioRxiv2026

The City Nature Challenge increases urban biodiversity knowledge and public engagement with blue spaces

Global biodiversity is declining at an unprecedented rate due to rapid environmental change and increasing human pressures. Ongoing urban expansion fragments natural systems, while urban design increasingly seeks to mitigate these impacts through the integration of blue-green infrastructure. Effective biodiversity monitoring is therefore essential to evaluate ecological conditions within these novel socio-ecological systems. Although urban biodiversity monitoring is challenged by its high landscape heterogeneity, dense human populations provide opportunities for large-scale data collection through public participation in citizen science. Using data from 25 City Nature Challenge (CNC) projects across the United Kingdom (2020-2025), we assessed the effects of the four-day bioblitz on species inventories, participation in biological recording, and spatial patterns of recording effort. CNC events doubled public participation in iNaturalist recording relative to baseline activity, leading to the documentation of numerous previously unrecorded species through increased observer effort and broader use of urban blue-green spaces. These results show that CNC events enhance urban biodiversity datasets by increasing the number of observers and reducing spatial and observer biases, providing a cost-effective tool for enriching urban biodiversity data. In addition to generating ecological data, CNC events could have public health benefits through increased exposure to urban blue-green spaces.

ecology↗

bioRxiv2025

Just add water: Urban blue spaces increase avian richness and functional diversity

Urban blue spaces are highly valuable for both people and nature, providing key ecosystem services, including flood alleviation, pollution absorption, microclimate regulation, benefits to human health and wellbeing, and habitat provision. Crucially, urban blue spaces support biodiversity, including threatened species, and despite often being small, may have disproportionate effects on their surrounding environment, acting as critical habitats within urban systems. However, research on the role of urban blue spaces within ecological contexts remains limited. Here, we assessed urban bird communities across green and blue spaces to quantify the ecological effects of urban water bodies. We surveyed birds along 22 paired 1 km transects in the city of Kingston Upon Hull, UK, recording species and abundance across both winter and breeding seasons. Our findings indicate that blue spaces significantly increase bird species richness during summer (P = 0.016), though not in winter. However, we found that the taxonomic distinctiveness of bird communities is consistently greater around blue spaces across both seasons (P < 0.05). Similarly, functional diversity based on species-level ecological traits was more varied around water (P = 0.01). In addition, we show that urban blue spaces could be important for avian conservation, supporting more red and amber-listed species than green spaces during the summer (P = < 0.05). Overall, our results show that urban blue spaces play a critical ecological role within cities by enhancing the complexity of avian communities, which in turn could improve human wellbeing and contribute to urban sustainability.

ecology↗