The Communication of Intraspecific Aggression in the Common Loon

THE role of the yodel call in the communication system of the Common Loon, Gavia iraruer, has not been well understood or extensively investigated. Previous studies provide only limited description and discussion of the occurrence and/or social significance of the yodel, and its territorial importance has been noted only briefly. Yeates (1950), studying several Icelandic lakes for two spring seasons, did not observe the yodel; and Munro (1945) did not mention it in his discussion of loon activity in the Cadboo Parklands. Dunlop (1915) described only the auditory features of the call. Olson and Marshall (1952: 24-25) professed the impossibility of describing and interpreting the yodel, but noted several instances of its performance: They reported that the yodel was given during the "reverberating" night choruses and at dusk and night by loons flying in wide circles over other loons on the lake. Further, they wrote that the yodel indicated "annoyance or disturbance" to seaplanes taking off, and reported one occasion where a tremolo (laugh) call "gave way" to a yodel when a pair's territory was intruded upon by humans. Hantszch (1928) associated the yodel with distress or pain. The yodel was also interpreted as a "love song" (Sire 1923) or reproductive call (Palmer 1962: 25), but reports of Common Loon reproductive behavior (Southern 1961, Tate 1969, Tate and Tate 1970, Sji51ander and Agren 1972) do not indicate that the yodel is related in any direct manner to either courtship or copulation. Recently, Sji51ander and Agren (1972) sketchily described the yodel as a "territorial marking" that occurred "most frequently during the first phase of reproduction" and was "heard only from owners of territories." Yet despite this current recognition of the territorial significance of the yodel, no account of the call as it is actually performed by loons defending or expanding their territories seems to have been reported. Further, aside from a scant reference by Sire (1923) to head position during yodeling, there appears to have been no mention of any posturing associated with the yodel call. This report presents field observations of the yodel call, a specific "crouch" posture frequently found with the yodel, and the encounters of displaying loons, discussed in terms of the communication and control of intraspecific aggression.