Adjusting to urban stress: How Eurasian tree sparrows modulate multiple physiological and nutritional markers across...

Numerous bird species have adapted to rapid urbanization, navigating challenges introduced by novel stressors. While prior research has explored how urban exploiters adjust their physiology relative to their rural counterparts during breeding season, the modulation of multiple physiological markers outside of reproduction, and the maintenance of sex-specific differences, remain less understood. Using an urban exploiter, the Eurasian tree sparrow (ETS; Passer montanus), we investigated how both sexes of urban and rural populations modulate twenty-two physiological markers of nutrition, body condition, oxidative stress, and antioxidative responses during pre-breeding stage. Our results showed that urban ETSs displayed distinct glucolipid metabolism compared to rural ETSs, characterized by higher levels of free fatty acids, β-hydroxybutyric acid, high-density lipoprotein (HDL), and total cholesterol, alongside lower levels of triglycerides, glucose (Glu), and fat content (FC). No significant differences were observed in other physiological markers. Additionally, both sexes of urban ETSs exhibited similar profiles across these markers, unlike rural populations where females showed higher Glu and total protein levels and lower HDL and FC levels than males. Our findings suggest that birds adjust their nutritional physiological markers in response to urbanization, likely due to dietary differences between urban and rural environments. Furthermore, sex differences in physiological markers of nutrition, body condition, oxidative stress, and antioxidant responses appear to diminish in urban settings.