Temporal pattern of vocalization type usage in singing sessions of male tyrant flycatchers (Tyranninae)

Abstract

It has been hypothesized that variation (e.g., of repertoire elements) in prolonged vocalization sessions of passerine birds can serve to minimize habituation by conspecifics. The repertoire of vocalization types limited in suboscine passerines, raising the question of how a limited set of elements can create patterns that minimize habituation. This question was studied by computational analysis of recorded singing sessions of 20 suboscine species from the subfamily Tyranninae, family Tyrannidae (tyrant flycatchers). The recordings of 12 of the species included two or more distinct vocalization types (VTs). In these species, the interval between vocalization units when the VT changed was on average shorter than that when the VT remained the same. In addition, when the VT changed, the mean interval length between successive vocalization units differed depending on which VT preceded the interval and which VT followed it. On the other hand, species with just a single VT in the session analyzed showed a surprisingly high degree of absolute difference between adjacent vocalization units with respect to both the length of the vocalization and percentage of time elapsed until peak amplitude. A change in the rhythm of vocalization accompanying a change in VT provided a potential means of drawing a conspecific listener's attention to the change in VT. The results showed that tyrant flycatchers use temporal patterning to achieve a high level of variety in vocalization sessions despite a limited vocal repertoire.