Multifunctionality in the Tremolo Vocalization of the Common Loon

Abstract

In the current literature on common loon vocalization, the most often-stated function of the tremolo call is as a general purpose alarm. I conducted tremolo playback experiments on Lake Temagami to test for added complexity in the call’s function. Playback experiments varied by type of call broadcasted (neighbor or stranger), group type of subject (single loon, pair of loons, or raft), and season (breeding, or post-breeding). In conducting this study, I observed playback responses in many contexts—some territorial, some defensive, some in pair bonding, some in group bonding. The purpose of the call seemed to vary with time and environment. My research thus suggests that the tremolo call is more than just an alarm call; it may be a sophisticated, context-dependent multifunctional mechanism. Generalized Linear Models showed that aggression in response to the tremolo call fell between the breeding season and the post-breeding season. Student t- Tests revealed that neighbor tremolo calls prompted a greater response in loons during playback trials than did stranger calls. Also, tremolo playback in the post- season prompted vulture-running and splash-swimming behaviors, whereas these behaviors were never observed in response to the tremolo call during the breeding season. Finally, Principal Component Analyses revealed no correlated variances in the suite of recorded response variables. These changes in response to tremolo calls, and lack of coordinated variance, point to the multifunctional nature of the vocalization. My observations and research suggest that, in addition to alarm signaling, the tremolo plays a role in territoriality and aggression, conspecific location awareness and peace-keeping, and group bonding before winter migration.