Roadway infrastructure is a dominant feature of landscapes across the globe, and the ecological and evolutionary impacts of these roadways are leading to declines in many natural populations. Research on the genetic impacts of roadways on bird populations has produced mixed results, with some studies revealing significant correlations between roads and genetic differentiation and others failing to resolve any relationship. Here, we use a whole-genome dataset of 61 California quail (Callipepla californica), a ground-dwelling and ground-nesting bird species, to quantify the impacts of roadway infrastructure on population genetic differentiation and measures of overall genomic health. To collect tissues for genomic analyses, we non-lethally sampled wild quail from populations located on either side of major and minor roadways in Southern California, a region with the densest road network in the United States. Using a variety of independent landscape genetic and statistical models, we demonstrate that roadways are an important factor shaping patterns of genomic differentiation in southern California quail populations. We also show that quail populations sampled along two of the busiest roadways traversing southern California have higher levels of inbreeding than other populations within the region, likely resulting from close sibling matings within the last 10 generations. These results highlight the importance of roads as major disturbances to genetic connectivity of wild populations and can help inform regional connectivity conservation efforts, including the construction of the Wallis Annenberg Wildlife Crossing over the US 101 freeway.

Joseph Curti, Ph.D. (he/they) is a postdoctoral research fellow at the UCLA La Kretz Center for California Conservation Science. Joey’s current research focuses on the impacts of anthropogenic stressors on bat community composition in urban areas across California. Joey received his Ph.D. in 2024 from the UCLA Ecology and Evolutionary Biology department, where he worked with statewide resource managers on a variety of conservation genomics projects. These included a project aimed at evaluating the impact of roadways in Los Angeles to California quail (Callipepla californica) gene flow and rangewide landscape genomics of the Yuma myotis bat (Myotis yumanensis).