Displays of Sayornis Phoebe (Aves, Tyrannidae)

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Abstract
(1) This report describes the behavior of communicating individuals of Sayornis phoebe (a North American tyrant flycatcher) and emphasizes the employment of the vocal repertoire. This comprises eight calls, of which only three are used commonly and in many contexts. Each of the remaining five occurs in fewer contexts, and all five may be restricted to the pair bonding and nesting phases of the annual behavioral cycle. The visible displays were studied less closely. Eight were identified, some of which were very rare. (2) Most attention was given to the vocalization commonly called "song" (herein Regularly Repeated Vocalization, RRV) which comprises two largely discrete units, the RR1 and RR2. These specify the identity of the communicator, and appear to indicate the existence of association tendencies which are non-aggressive in the case of the RR1, but occur with aggressive tendencies in the RR2. Association tendencies were inferred when an individual persistently remained near another individual (or sometimes a nest site) without attempting any form of contact behaviour. This was most commonly seen when the male of a pair associated with his mate (often without displays) wherever she went in the territory. RRV, however, was usually uttered in the absence of a visible recipient; if the recipient did appear the communicator associated at a distance or ceased using RRV and employed other displays. (3) The message of song is variable and determined by the relationships of its components. That is, changing combinations of the RR1 and RR2 appear to provide an index of the shifting mood of the singing individual. During continuous RRV calling the degree to which each unit is represented provides a relevant context for the other unit according to a temporal pattern which I have measured by "string length", and which could also be measured by the relative frequencies of occurrence per unit time. The varying relationships between the two units seems always to be patterned; only one case of RRV could be shown even to approach a random distribution. (1) This report describes the behavior of communicating individuals of Sayornis phoebe (a North American tyrant flycatcher) and emphasizes the employment of the vocal repertoire. This comprises eight calls, of which only three are used commonly and in many contexts. Each of the remaining five occurs in fewer contexts, and all five may be restricted to the pair bonding and nesting phases of the annual behavioral cycle. The visible displays were studied less closely. Eight were identified, some of which were very rare. (2) Most attention was given to the vocalization commonly called "song" (herein Regularly Repeated Vocalization, RRV) which comprises two largely discrete units, the RR1 and RR2. These specify the identity of the communicator, and appear to indicate the existence of association tendencies which are non-aggressive in the case of the RR1, but occur with aggressive tendencies in the RR2. Association tendencies were inferred when an individual persistently remained near another individual (or sometimes a nest site) without attempting any form of contact behaviour. This was most commonly seen when the male of a pair associated with his mate (often without displays) wherever she went in the territory. RRV, however, was usually uttered in the absence of a visible recipient; if the recipient did appear the communicator associated at a distance or ceased using RRV and employed other displays. (3) The message of song is variable and determined by the relationships of its components. That is, changing combinations of the RR1 and RR2 appear to provide an index of the shifting mood of the singing individual. During continuous RRV calling the degree to which each unit is represented provides a relevant context for the other unit according to a temporal pattern which I have measured by "string length", and which could also be measured by the relative frequencies of occurrence per unit time. The varying relationships between the two units seems always to be patterned; only one case of RRV could be shown even to approach a random distribution.

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