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 sh aring, and singing mode, and identify some of the correlates of this variat ion. 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 frequen cy-modulated whistles or note complexes and a loud terminal trill. Song typ es 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 e ach other in northwestern Costa Rica. Song-type sharing between neighboring males averaged 77% (range 48 to 90%) and was significantly higher among ma les inhabiting a continuous forest habitat area (78%) than among birds in t wo broken-forest/second-growth areas (62%). Populations separated by 8 km s hared few song types (10%). Singing mode encompassed both the immediate var iety and eventual variety patterns found in other passerines, as well as a continuous range of intermediate variety between these two extremes. We use d switching rate and a modified Shannon-Wiener index of song-type diversity to quantify variation in singing modes. High-switching, high-diversity sin ging was associated with the dawn chorus and with soft singing in the prese nce 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 durin g and after highly escalated boundary encounters. Thus, unlike most discret e-repertoire species described to date, Banded Wrens decreased their switch ing rate in increasingly agonistic contexts.