A REVERSED PATTERN OF ASSOCIATION BETWEEN SONG DIALECTS AND HABITAT IN THE RUFOUS-COLLARED SPARROW DARI ´ O A. LIJTMAER 1 AND PABLO L. TUBARO Divisio ´n Ornitologı ´a, Museo Argentino de Ciencias Naturales ‘‘Bernardino Rivadavia,’’ Av. A ´ ngel Gallardo 470, C1405DJR, Buenos Aires, Argentina Abstract. We studied song dialects of the Rufous-collared Sparrow (Zonotrichia capensis) in espinal woodland and steppe surrounding Guatrache ´ Lake in Argentina. We recorded 150 individuals and analyzed 14 quantitative song variables. There were significant differences between habitats in song temporal structure. In particular, the internote interval of trills was shorter in the closed compared to the open habitat. This pattern is the reverse of what is usually found in this species, although it has previously been detected in another area of the region in which this study was conducted. This region is characterized by strong winds, which could be related to the reversed pattern found. Song frequencies were lower in the closed woodland habitat than in the open steppe, which also contrasts with the pattern usually found in this species. We also recorded and analyzed the songs in a portion of the area in which the woodland was converted into grassland during the last century. The temporal structure of songs in the converted area was intermediate between song structures in the original habitats and frequencies were lower in the converted area than in both original habitats. Song structure appears to have changed after habitat conversion, but this cannot be confirmed with the data at hand because of the lack of recordings obtained before habitat change. Key words: acoustic adaptation hypothesis, dialects, Guatrache ´ Lake, Rufous-collared Sparrow, Zonotrichia capensis. Un Patro ´ n de Asociacio ´ n Invertido entre los Dialectos de Canto y el Ambiente en Zonotrichia capensis Resumen. Se estudiaron los dialectos de canto de Zonotrichia capensis en el bosque de espinal y la estepa de los alrededores de la Laguna de Guatrache ´ en Argentina. Se grabaron 150 individuos y se analizaron 14 variables cuantitativas del canto. Se encontraron diferencias significativas entre los ambientes en la estructura temporal del canto. En particular, el intervalo entre las notas del trino fue menor en el ambiente cerrado que en el abierto. Este patro ´n esta ´ invertido en relacio ´ n al que suele encontrarse en esta especie, pero ha sido encontrado previamente en otra a ´rea de la regio ´n en donde se llevo ´ a cabo este estudio. Dicha regio ´ n esta ´ caracterizada por la presencia de fuertes vientos, los cuales podrı ´an estar relacionados con el patro ´ n invertido encontrado. Las frecuencias del canto fueron menores en el ambiente cerrado que en el abierto, lo cual tambie ´n contrasta con el patro ´ n encontrado generalmente en esta especie. Tambie ´n se grabaron y analizaron cantos de una porcio ´n del a ´rea en la cual el espinal fue convertido en pastizal durante el siglo pasado. La estructura temporal del canto en el a ´ rea convertida fue intermedia entre las estructuras de los ambientes originales y las frecuencias fueron menores en el a ´ rea convertida que en ambos ambientes originales. La estructura del canto parece haber cambiado luego de la conversio ´ n del ambiente, pero esto no puede ser confirmado con los datos disponibles debido a la falta de grabaciones obtenidas antes de dicha conversio ´n. INTRODUCTION Acoustic signals attenuate and become modi- fied during transmission (Morton 1975, Wiley and Richards 1978, 1982, Richards and Wiley 1980). The Acoustic Adaptation Hypothesis proposes that bird songs are structured to maximize performance under the environmen- tal acoustics of their native habitat (Morton 1975, Brown and Handford 1996, 2000). To achieve this, the structure of songs used in long- range communication should minimize attenu- ation (Morton 1975), degradation (understood as ‘‘the sum of all the changes in the signal at distance X relative to the signal’s structure at its origin’’; Morton 1986:69), or degradation var- iability (Brown and Handford 1996, 2000). Manuscript received 25 May 2006; accepted 26 January 2007. 1 E-mail: dlijtmaer@macn.gov.ar The Condor 109:658–667 # The Cooper Ornithological Society 2007 [658]