Microgeographic variation and sharing of the gargle vocalization and its component syllables in black-capped chickadee (Aves, Paridae, Poecile atricapillus) populations

Throughout the year during agonistic encounters, black-capped chickadees (P oecile atricapillus) emit a vocal signal known as the gargle call. Each bir d has a repertoire of structurally differing gargle calls; some are shared with others in the local area. As a basis for understanding the cultural ev olution of this social signal, we initiated a study of gargle call repertoi res of birds living in a narrow belt of continuous riparian habitat occupie d throughout by a resident population of chickadees. During two consecutive winter seasons, we sampled repertoires at three locations over a distance of 8.4 km to quantify micro-geographical variation. Analyses of vocal shari ng and population differentiation were carried out on whole gargle calls an d on the individual acoustic units (syllables) from which the whole calls a re constructed. We analysed 28 380 calls of 46 subjects in the two seasons of study. Birds averaged 7.6 different calls in their gargle repertoires. C alls were composed of about 10 syllables on average. Fifty-six different sy llables were used to construct the calls of all birds. Each study site had some gargle calls unique to the local birds and some that were shared with one or both of the other two sites. There was significantly greater sharing of both calls and syllables among birds within sample sites than between s ample sites. The frequencies of the different kinds of gargles and syllable s were significantly correlated across the 2 yr of the study, but the corre lation was stronger (r(2) = 0.93) for syllables than for whole gargle calls (r(2) = 0.61).