Data from: Song rate as a signal of male aggressiveness during territorial contests in the wood warbler

Aggressive signaling is an important component in animal communication, as
it provides an efficient mechanism for settling conflicts over resources
between competitors. In songbirds, a number of singing behaviors have been
proposed to be aggressive signals used in territory defense, including
song rate. Although aggressive signaling in songbirds has received
considerable research attention, adequate evidence for most putative
aggressive signals is not available. In this study, we experimentally
investigated whether the song rate of male wood warblers (Phylloscopus
sibilatrix) is a signal of their aggressive intent in male-male
interactions. We found that males responded differentially to simulated
territorial intrusions depending on the song rate of an intruder.
Moreover, males that continued to sing during territorial contests
increased their song rates, and this behavior predicted the strength of
aggressive escalation by the signaler. These results suggest that song
rate is an aggressive signal during male-male interactions in the wood
warbler. We also found high intra-individual repeatability in the strength
of aggressive response to simulated intrusions, likely reflecting
differences in personality (aggressiveness) or quality of male wood
warblers. We conclude that changes in singing rate may be an efficient
mechanism of signaling immediate shifts in motivation of signalers during
territorial contests, especially in species that lack large repertoires or
have simple songs.