Physiological consequences of urbanization to Sonoran Desert birds

As cities expand worldwide, understanding how species adapt to novel urban habitats will become increasingly important to conservation. The adrenocortical stress response enables vertebrates to cope with novel environmental challenges to homeostasis. We examined baseline and stress-induced corticosterone (CORT) concentrations in three songbird species within and around Phoenix, Arizona. We tested whether baseline and stress-induced CORT patterns differed among species living at varying densities in Phoenix and tested the hypothesis that, for species capable of successfully colonizing cities, individuals living in urban areas have a decreased acute stress response compared to individuals living in native desert. Baseline CORT levels were generally similar in urban and desert birds. Capture and handling stress typically produced greater total CORT responses in urban birds than in desert birds, although these responses differed as a function of sampling date. Urban birds showed less seasonal variability in stress responses than desert birds. We propose that more predictable resources in the city than in rural areas may decrease the need to vary stress responsiveness across life history stages. The results highlight the species-specific effects of urbanization on stress physiology and the difficulty to predict how urbanization impacts organisms.