The Interplay Between Urban Temperature and Feather Coloration: Factors Shaping Immunological Traits in Pigeons ( <i>Columba livia</i> )

The development of anthropogenic structures in cities has resulted in thermal heterogeneity, potentially affecting the immunological features of urban fauna. In these environments, synanthropic species such as pigeons (Columba livia) exhibit coloration polymorphisms under endocrine regulation mediated by the melanocortin system, which determines several immunological traits. Due to these potential sources of variability, we assessed how habitat influences physiological traits related to immunological features, theoretically affected by feather coloration, while considering other factors such as seasonality, body mass, and sex. This study aimed to determine whether pigeons from locations with different urban temperatures (Santiago, Chile) and color polymorphism exhibited variability in plasma immunoglobulin Y concentration, leukocyte profiles, and the H/L index. The results demonstrate that pigeons exhibit variations in immunological features related to the thermal characteristics of their urban habitats. Specifically, we observed a strong effect of thermal heterogeneity on the H/L ratio, with higher values in areas experiencing warmer temperatures, a relationship dependent on body mass. We also identified differential impacts of seasonality and sex on basophil and monocyte percentages. Regarding humoral immunity, we found a strong effect of environmental temperature and plumage melanism on urban pigeons which was influenced by sex. Our findings contribute to understanding the factors affecting the immune system in urban birds and provide valuable insights into their response to landscape modifications.