Song as an aggressive signal in the song sparrow Melospiza melodia

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)



First Committee Member

William A. Searcy - Committee Chair


This dissertation addressed aggressive signaling and the intrasexual function of male song in the song sparrow, Melospiza melodia. Using song playback techniques, I showed that male song sparrows in a Pennsylvania population with low levels of whole song type sharing can perform partial song matching using shared song segments. Partial song matching was associated with a stronger aggressive response than non-matching, suggesting that partial matching functions as a directed signal of aggression. In a separate playback experiment I tested the aggressive response of territorial males to partial-matching and non-matching songs. I asked whether a receiver-dependent cost, in the form of the receiver's aggressive retaliation, is a mechanism ensuring the signal reliability of partial matching. My results did not support the receiver-retaliation hypothesis. I present the first acoustic analysis of low-amplitude 'soft song', an especially aggressive behavior associated with subsequent attack in song sparrows. I present evidence for two types of soft song: 'crystallized' soft songs that are quiet versions of repertoire song types, and 'warbled' soft songs that are not found in the repertoire. Using playback I tested for a receiver-retaliation rule for soft song, taking into account both 'crystallized' and 'warbled' types of soft song. Males responded equivocally to normal broadcast song vs. soft song, and also to crystallized vs. warbled soft song. A receiver retaliation cost is the most plausible category of cost to apply to a signal such as soft song, but such a cost is not supported by my results. To further address male perception of soft song, I examined patterns of the cardiac response (change in heart rate) to song and other stimuli in male song sparrows. I monitored the heart rates of caged territorial males during playbacks of song sparrow broadcast song, soft song, alarm calls, and a predator call, and measured the shape, magnitude and duration of the evoked cardiac responses. Broadcast song and alarm calls evoked the strongest cardiac responses, and soft song evoked the least response. These results do not support the hypothesis that soft song is highly aversive.


Biology, Ecology; Biology, Zoology

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