Urbanization is a rapidly expanding global phenomenon that significantly changes natural habitats, often forming novel ecosystems characterized by various urban features. These changes affect bird species, including Cardueline finches, like lesser goldfinches (Spinus psaltria), house finches (Haemorhous mexicanus), and pine siskins (Spinus pinus), which are common in California and frequently found near bird feeders. In urban environments, these birds face stressors such as elevated noise, light pollution, chemical exposure, and increased human activity. These stressors can also affect vectors of bloodborne parasites, such as avian haemosporidians, impacting parasite-host dynamics. To test whether urban stressors result in an elevated stress response, we quantified the heterophil/lymphocyte (H/L) ratios in finches, across an urban-rural gradient. H/L ratios are a well-known indicator of stress and immune function in birds. We hypothesize that urban-dwelling Cardueline finches will show higher H/L ratios, reflecting a stress response due to the prevalence of stressors in urban environments. To control for H/L ratios, we are quantifying parasitemia of haemospordians and other bloodborne parasites, as acute infections are expected to elevate these ratios. Our findings will provide insights into how urbanization influences the stress and immune response of finches, contributing to a broader understanding of how urbanization impacts wildlife health.