Repertoire Size, Repertoire Overlap, and Singing Modes in the Banded Wren (Thryothorus pleurostictus)

We describe the song system of the Banded Wren (Thryothorus pleurostictus), with emphasis on within-species variation in repertoire size, song-type sharing, and singing mode, and identify some of the correlates of this variation. Unlike most of its duetting congeners, males are the primary songsters in this species. Songs are discrete, 2 to 5 s in duration, and consist of softer introductory buzzes and rattles followed by several repeated frequency-modulated whistles or note complexes and a loud terminal trill. Song types are highly distinctive. Repertoire size averaged 19.7 song types (range 15 to 24) and did not vary among three populations located within 8 km of each other in northwestern Costa Rica. Song-type sharing between neighboring males averaged 77% (range 48 to 90%) and was significantly higher among males inhabiting a continuous forest habitat area (78%) than among birds in two broken-forest/second-growth areas (62%). Populations separated by 8 km shared few song types (10%). Singing mode encompassed both the immediate variety and eventual variety patterns found in other passerines, as well as a continuous range of intermediate variety between these two extremes. We used switching rate and a modified Shannon-Wiener index of song-type diversity to quantify variation in singing modes. High-switching, high-diversity singing was associated with the dawn chorus and with soft singing in the presence of the male's mate. High-switching, low-diversity singing (alternation between two or three song types) was associated with countersinging from a distance. Low-switching, low-diversity singing (repeat mode) occurred during and after highly escalated boundary encounters. Thus, unlike most discrete-repertoire species described to date, Banded Wrens decreased their switching rate in increasingly agonistic contexts.