Pigeons are assumed to be common in most urban areas, but St. Louis does not have as many of these birds compared to other major cities. Washington University researchers have found that urban design and planning has a lot to do with that pigeon disparity, which highlights what’s missing in the city’s ecosystem. Postdoctoral fellow Elizabeth Carlen shares why a lack of pedestrians is the culprit, and how curiosity about minimal pigeon sightings in St. Louis landed her and her research partners in Madrid, Spain.