Scientists are analyzing a rare snapshot in time of urban plants and animals. To better understand whether rapidly growing cities are hosting the same species, a concept known as urban homogenization, a team from the California Academy of Sciences analyzed an immense volume of data gathered by citizen scientists during the four-day global City Nature Challenge. The 14 U.S. cities included in the study amassed more than 65,0000 wildlife observations identified to species level through the mobile app iNaturalist. Study findings suggest that despite similarities across cities, urban biodiversity still strongly reflects the species that are native to a region. However, observations of shared “cosmopolitan” species like pigeons, white-tailed deer, and dandelions were more numerous than locally occurring species. The study, published today in the journal PeerJ: Life & Environment, highlights the value of citizen science data in addressing complex questions about rapid changes in urban ecology.