[287] The Condor 103:287–297 q The Cooper Ornithological Society 2001 GEOGRAPHICAL VARIATION IN THE CALLS OF THE CHOUGHS 1 PAOLA LAIOLO 2 AND ANTONIO ROLANDO Dipartimento di Biologia Animale e dell’Uomo, Via Accademia Albertina 17, 10123 Turin, Italy ANNE DELESTRADE Centre de Recherches sur les Ecosyste `mes d’Altitude, 400 Route du Tour, Montroc, 74400 Chamonix, France AUGUSTO DE SANCTIS C.A.R.F. c/o WWF-Abruzzo, C. P. 317, 65100 Pescara, Italy Abstract. The calls of 22 populations of the Red-billed Chough (Pyrrhocorax pyrrho- corax) and the Alpine Chough (P. graculus) were sampled throughout the Palearctic region. In both species calls differed in frequencies, either by latitude or longitude in the Red-billed Chough and mostly by longitude in the Alpine Chough. Frequencies varied according to body size, being higher in smaller-bodied populations and lower in larger-bodied ones, as predicted by the inverse relationship between body size and frequency. We hypothesize that, besides the effect of physical constraints determining frequencies, past climatic events and the geomorphological history of the Pleistocene also have influenced the present pattern of diversification. We also hypothesize that gene flow and ‘cultural’ flow have constrained the evolution of clear-cut population differences between European and North African popula- tions, whose segregation could be quite recent. Key words: Alpine Chough, geographical variation, Pyrrhocorax graculus, Pyrrhocorax pyrrhocorax, Red-billed Chough, vocalization. Variacio ´n Geogra ´fica en las Llamadas de Pyrrhocorax Resumen. Muestreamos las vocalizaciones (llamadas) de 22 poblaciones de Pyrrhocorax pyrrhocorax y P. graculus a lo largo de la Regio ´n Palea ´rtica. En ambas especies las llamadas variaron en frecuencia, tanto en latitud como longitud para P. pyrrhocorax y ba ´sicamente en longitud para P. graculus. Como predice la relacio ´n inversa entre taman ˜o corporal y frequencia, las frecuencias fueron ma ´s elevadas en poblaciones con taman ˜ o corporal pequen ˜o y fueron ma ´s bajas en poblaciones con taman ˜o coporal mayor. Hipotetizamos que, ma ´s alla ´ del efecto de las restricciones fı ´sicas que determinan la frecuencia, eventos clima ´ticos pa- sados y la historia geomorfolo ´gica del Pleistoceno tambie ´n han influenciado el patro ´n actual de diversificacio ´n. Tambie ´n hipotetizamos que el flujo ge ´nico y ‘cultural’ han restringido la evolucio ´n de diferencias marcadas entre poblaciones de Europa y Africa del Norte, cuyas segregaciones podrı ´an ser particularmente recientes. INTRODUCTION We investigated the patterns of geographic var- iation in the calls of the Red-billed Chough (Pyrrhocorax pyrrhocorax) and the Alpine Chough (Pyrrhocorax graculus), two corvid species with a broad Palearctic distribution, ranging from Europe and northwest Africa to west China; an isolated population of the former species also inhabits Ethiopia (Goodwin 1986). Several studies have used vocalizations to eval- uate the degree of geographic differentiation of natural populations of passerines (Mundinger 1982, Kroodsma et al. 1984). The presence of 1 Received 23 June 2000. Accepted 22 November 2000. 2 E-mail: laiolo@dba.unito.it local dialects in oscine birds is among the most striking examples of geographic variation in song, whereas non-songbirds are usually ne- glected in questions of acoustic geographic var- iability because their vocalizations are regarded as invariable (Payne 1982, Martens 1993, 1996). To date, corvid vocalizations, lacking the typical advertising songs of most other passerine groups, have rarely been investigated. Similarly, intraspecific geographic variation in the vocali- zations of corvids has rarely been studied. The great individual variation within call types and the trivial functional and phonetic differences between call types possibly discouraged such studies (Cramp and Perrins 1994). When making intraspecific comparisons of vocalizations, it is worth noting that variation due to cultural evo-