SICB 2019: Female Aggression in Song Sparrows is Higher in Urban Habitats

Urbanization has repeatedly been shown to negatively impact wild animals and is a particular concern for wild birds. Fortunately, some species are able to flexibly alter their behavioral phenotypes and adapt to the busy life in the city. Resource competition may be higher in urban environments, thereby selecting for more aggressive behaviors in city-slicking birds. Sam Lane, a PhD student in Kendra Sewall’s lab at the Virginia Polytechnic Institute and State University addressed this hypothesis by comparing patterns of aggression to conspecifics in female song sparrows (Melospiza melodia) between urban and rural habitats.

Lane tested his hypothesis by simulating the intrusion of a conspecific female onto the social territory of focal females at two rural and two urban study sites in Blacksburg, VA. Specifically, Lane placed a model female song sparrow within 5-10 meters of the focal bird’s nest and played one of 6 exemplars of previously recorded female vocalizations. He then measured the focal female’s distance from the speaker and the number of chitters, chets, growls, and buzzes produced by the female as a measure of aggression. He did this for 3 minutes without the model and 6 minutes after exposing the model.

Lane found that female song sparrows nesting in urban habitats were more likely to respond to a simulated female intruder and showed a greater behavioral response to conspecific intrusions than did females in rural habitats. Further, his results parallel prior work looking at aggressive behaviors in urban male song sparrows. Sewall’s group hypothesize that song sparrows behave as urban adapters and increase territorial aggression in response to increased resource competition.