Research Description

Song sparrows, also known as Melospiza melodia, are songbirds commonly found all over North America. Males perch in all sorts of bushes and tree branches and sing to declare their presence and dominance over a territory. They whip up song after song, especially when an intruder ventures within the territory boundaries. With the entrance of an intruder often comes a dip in the volume of Melospiza’s song, sometimes barely audible in contrast to the loud songs one can hear walking by on a sunny day. We know soft song occurrence is more frequent in such aggressive encounters, however, we are not sure why these birds lower their voices. There are several hypotheses on the matter. The first is that they sing quietly to avoid eavesdropping by nearby conspecific males, because in this situation the territory holding male is more vulnerable to extra intrusions. A recent study looked more closely at this and did not find a relationship, however. Another hypothesis is that the quiet song is a byproduct of Melospiza’s body positioning in close encounters with other males. This readiness hypothesis has not been closely examined as of now. The third hypothesis, and the one we are working on, is that quiet song is selectively advantageous in that it helps song sparrows avoid predation. Interactions are bound to draw attention birds duking for ground. Therefore it is possible quiet song keeps auditory spotlighting by predators to a minimum.

Our study tests this hypothesis by exposing males whose territory is threatened to the predatory stimulus of a Cooper’s hawk. To do this, we first expose an individual Song Sparrow to another Melospiza’s song, alerting them to an intruder, then, after a few minutes we play either a Cooper’s hawk stimulus or a control. We record the interactions, and take note of the number of times an individual sings quiet and loud song. Our research was conducted in March at Discovery Park and we are now in the process of scanning data from recordings. Once we are done scanning, we hope to know more about the reason behind hushed voices in Song Sparrows.