Geographic diversification in the call repertoire of the genus Pyrrhocorax(Aves, Corvidae)

We analysed the call repertoires of the Red-billed Chough (Pyrrhocorax pyrr hocorax) and the Alpine Chough (Pyrrhocorax graculus) across three continen ts (Europe, Asia, and Africa) for intraspecific and interspecific differenc es in call-repertoire size and discuss the factors that could have promoted its evolution. The overall call repertoire of the Red-billed Chough was tw ice as large as that of the Alpine Chough, but the number of calls recorded in each population did not differ significantly between the two species. T he greater fragmentation of the range of the Red-billed Chough possibly ind uced its remarkable call-repertoire diversification. Some populations (i.e. , those from Ethiopia, Central Asia, Canaries) had a peculiar call repertoi re that overlapped very little with those from other regions; consequently, the overall numbers of call types within the species were heavily influenc ed by these unusual populations and were very large. The call-repertoire si ze and call-repertoire similarity of populations of both species were affec ted and constrained by geographic distance. More closely situated or contin ental populations tended to have a more similar pool of calls (this is prob ably due to mingling among close populations).