Behavior, Physiology, and Reproduction of Urban and Rural Song Sparrows (Melospiza Melodia)
Urban areas are a unique and growing habitat type. Animals living in this novel habitat are faced with new challenges, but may also encounter novel opportunities. Though urban animals have been observed to differ from their rural counterparts in a variety of behavioral and physiological traits, little is known about the specific features of urban areas that drive these differences and whether they are adaptive. Understanding this process is important from a conservation perspective and also to gain insight into how animals colonize novel habitats more generally. Using song sparrows (Melospiza melodia), a native songbird commonly found in urban areas, I explored responses to urbanization and the drivers and consequences of these responses with an eye toward understanding whether song sparrows had successfully adapted to urban habitats (Chapter I). I began by comparing body condition and levels of corticosterone, a hormone associated with energy management and the stress response in birds, between urban and rural populations (Chapter II). There was more variation across years than between habitats, suggesting that a variable environmental factor common to both habitats is the primary driver of these traits. I then compared territorial aggression levels and tested the effect of food availability on aggression (Chapter III). Fed rural birds and all urban birds had higher aggression levels than unfed rural birds, indicating that territorial aggression is related to resource availability in this species and that urban habitats may be perceived as more desirable. Finally, I looked for differences in reproductive timing and success and for relationships between reproductive success and aggression (Chapter IV). Higher reproductive success in urban populations, coupled with differences in the timing of successful nests between habitats, suggest differences in predation risk and predator community structure between habitats. In Chapter V, I synthesize my major findings and suggest directions for future research building on these results. I conclude that urban song sparrows differ from rural birds, that these differences are influenced by resource availability, and that urban habitats can potentially support stable song sparrow populations, though more research is necessary to determine the fitness impacts of specific traits that change with urbanization.