Black-capped chickadee call dialects along a continuous habitat corridor

The gargle call, a vocalization us ed in agonistic encounters by black-capp ed chickadees, Poecile atricapillus, was examined for evidence of geographi cal variation along a corridor of continuous riparian habitat in northern C olorado. We captured birds from three different sites during the nonbreedin g season and brought them into the laboratory, where their gargle calls wer e 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 populati on repertoires. The majority (88.7%) of gargle types analysed were found to be unique to individual populations rather than shared among or between po pulations. Examination of individual repertoires showed that chickadees sha red a higher proportion of gargle types with birds from their own sites com pared with birds from either of the two other sites. Thus, gargle dialects occurred among these chickadee population despite the absence of geographic al barriers to blending of vocal traditions. As the birds studied were obta ined from sites along an uninterrupted dispersal corridor, the results of t his study suggest that behavioural mechanisms are responsible for maintenan ce of dialects in this aggressive call. (C) 1999 The Association for the St udy of Animal Behaviour.