Dynamics of Territorial Singing Between Neighboring Song Sparrows (Melospiza Melodia)

Abstract

1. Countersinging song sparrows (n = 6) interact by coordinating the turnover of their song bouts, but long-term leader/follower roles generally do not occur in song switching. In contrast, varition in the sequencing of song types and in the rate of singing are not influenced by that of countersinging neighbors. 2. Singing was divided into four behavioral contexts (soloing, countersinging, pre-fight and post-fight) in which the intensity of agonistic stimulation was assumed to increase. Both bout lengths and the coordination of song switching with perch changing showed consistent relationships with stimulus intensity; however, the periods of songs (a measure of timing) showed no such relationship. 3. The relative frequencies of occurrence of song types within repertoires changed across the four behavioral contexts, although this change could be a by-product of the correlation between bout length and context. 4. In general, variations in the song sparrow's rate of switching song types are used in short-term interactions involving territorial defense, but variation in song type sequencing and song rates are not used. The benefits of song switching (which require the possession of at least two song types) cannot explain the origin of larger repertoires of song types. 5. We suggested these benefits may be the transmission of directional and motivational information. Given the large repertoires and low song sharing of this population, song switching may be better adapted for obtaining these benefits than song sequencing or song rates. 6. The tendency to coordinate song switches with perch changes was predicted by the Beau Geste hypothesis (KREBS, 1977), which assumes that singing is directed to unestablished floater seeking a territory. However, since this coordination tends to increase with increasing stimulation provided by territorial neighbors, it does not exclusively support the Beau Geste hypothesis.