Unraveling urban biodiversity through citizen science

Citizen or community science is becoming an increasingly important component of biodiversity monitoring in cities. While the term is associated with a multitude of interpretations, citizen science involves the engagement of volunteers in the scientific process, with the goal of generating knowledge that addresses a relevant problem or research question. Citizen science has the potential to improve scientific literacy, facilitate experiences with nature, and provide valuable training for careers in STEM. Outside of direct benefits to volunteers, citizen science has yielded global biodiversity datasets, species discoveries and rediscoveries, and early detections of invasive species. As urban areas grow, citizen science presents even more opportunities to monitor and conserve biodiversity in cities. In particular, urban ecologists have paid increasing attention to engaging audiences not traditionally represented in ecology. Lack of adequate representation reinforces systemic inequalities, creates gaps in data, and leaves out research questions that are important to participating communities. By implementing an ‘ecology with cities’ approach, citizen science has immense potential to cultivate a more inclusive generation of scientists and advance urban ecological knowledge. Thus, assessing the status of urban citizen science projects and how they engage volunteers is of critical importance. Herein, we review over 400 citizen science projects monitoring urban biodiversity globally. We describe the breadth of urban citizen science (CS) projects which monitor biodiversity in terms of their scope, scale, and aims; the variety of approaches employed for biodiversity monitoring; and the audiences targeted for participation in urban CS projects. Finally, we present case studies representing a range of geographic and cultural contexts to illustrate the various challenges and opportunities associated with improving representation in urban CS projects. We summarize recommendations informed by these case studies that citizen science practitioners can use to inform their own efforts to reach audiences not traditionally represented in ecology. We chart out future research directions for citizen science to innovate community-engaged research methods, promote conservation, and advance biodiversity monitoring in cities.