Meeting Abstract
Urbanization profoundly impacts the environment, creating novel habitats that differ vastly from surrounding non-urban habitats. This transformation may result in urban birds adjusting phenotypically such that they are better suited for the opportunities and challenges of their new habitats. To address this question, we compared free-ranging adult male Abert’s Towhees, Melozone aberti, sampled during their breeding season in urban (n = 16) and surrounding non-urban (n = 20) areas in metropolitan Phoenix, Arizona. Birds were caught and bled within two minutes (Initial), restrained for 60 minutes, bled again (Stress), measured, and released on site. Urban towhees were heavier and had longer wings than non-urban birds, but were in similar body condition and had similar visible fat reserves and sizes of the cloacal protuberance, an androgen-dependent secondary sexual characteristic. Urban birds had lower Initial plasma corticosterone (CORT) than non-urban birds, but the two groups of towhees increased plasma CORT to similar levels during stress, suggesting higher stress sensitivity in urban settings. The lysis and agglutination capacities of blood did not differ between non-urban and urban towhees, but in both groups decreased during stress, suggesting rapid modulation of immune function during a stressful event. In summary, the adjustment of Abert’s Towhees to urban areas involves changes in body size and in the endocrine, but not immune, response to acute stress. Supported by BCS-1026865, Central Arizona-Phoenix Long-Term Ecological Research (CAP LTER).
