Regional Dialects in the Contact Call of a Parrot
This study describes a system of regional dialects in the contact call of a parrot, the yellow-naped amazon (Amazona auropalliata). Spectrographic cross-correlation analyses of calls from multiple adults at 16 roosts in Costa Rica reveal two distinct patterns of geographic variation in call structure: first, variation in the basic structure of the call by which roosts can be classified into three distinct dialects, and second, finescale variation of call structure among roosts within a dialect. Some birds at roosts bordering two dialects use the calls of both neighbouring dialects interchangeably. These results suggest that there are two distinct processes governing the diffusion of call types among roosts, with dialect borders acting as barriers to the spread of foreign calls. Such a dialect system could be maintained through either reduced dispersal of birds across dialect boundaries or alternatively, by reduced diffusion of call types. These two possibilities have different implications for the genetic isolation of populations and thus for both speciation and learning. This pattern is broadly similar to those seen in some songbirds and may be maintained in a similar manner.