Black-capped chickadee call dialects along a continuous habitat corridor.

The gargle call, a vocalization used in agonistic encounters by black-capped chickadees, Poecile atricapillus, was examined for evidence of geographical variation along a corridor of continuous riparian habitat in northern Colorado. We captured birds from three different sites during the nonbreeding season and brought them into the laboratory, where their gargle calls were recorded. We sorted sonagrams produced from these vocalizations visually into distinct gargle types having similar compositions of individual units, or syllables. This allowed us to characterize both individual and population repertoires. The majority (88.7%) of gargle types analysed were found to be unique to individual populations rather than shared among or between populations. Examination of individual repertoires showed that chickadees shared a higher proportion of gargle types with birds from their own sites compared with birds from either of the two other sites. Thus, gargle dialects occurred among these chickadee populations despite the absence of geographical barriers to blending of vocal traditions. As the birds studied were obtained from sites along an uninterrupted dispersal corridor, the results of this study suggest that behavioural mechanisms are responsible for maintenance of dialects in this aggressive call. Copyright 1999 The Association for the Study of Animal Behaviour.