Is syntax a signal of aggression in hermit thrush (Catharus guttatus) song?

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University of New Brunswick


Syntax, which classifies the order song types must follow within a bird's song to convey functional meaning, is thought to play a role in songbird communication. Vocal cues are crucial to male-male interactions and certain species have been shown to alter their songs in response to territorial intruders (Hedley, Denton, & Weiss, 2017). The current study focuses on the use of syntax in aggressive contexts in the hermit thrush, a migratory songbird common to North America. Using playback sessions, this research evaluated the importance of species-typical syntax in conveying aggression in territorial disputes between two males. It was expected that the hermit thrush would react more strongly to songs which contained species-typical syntax than those which did not, however there was no difference in aggressive reactions between the two stimuli. These findings suggest that the hermit thrush may use syntax for other evolutionarily relevant behaviours, such as mate attraction. Vocal responses, including song overlapping and frequency matching, were also assessed and were both found to occur at below chance levels, indicating that birds actively avoided these behaviours during playback. Based on past research, it could be possible that birds are altering their songs to avoid acoustic interference, thus maximizing their signal transmission efficiency. Keywords: aggression, male-male interactions, hermit thrush, playback