Variation in chick-a-dee calls of a Carolina chickadee population, Poecile carolinensis: identity and redundancy within note types.

Chick-a-dee calls of chickadee species are structurally complex because calls possess a rudimentary syntax governing the ordering of their different note types. Chick-a-dee calls were recorded in an aviary from female and male birds from two field sites. This paper reports sources of variation of acoustical parameters of notes in these calls. There were significant sex and microgeographic differences in some of the measured parameters of the notes in the calls. In addition, the syntax of the call itself influenced characteristics of each of the notes. For example, calls with many introductory notes began with a note of higher frequency and longer duration, relative to calls with few introductory notes. Furthermore, the number of introductory notes influenced frequency and duration components of notes later in the call. Thus, single notes are predictive of the note composition of the signaler's call. This suggests that a receiver might gain the meaning in the call even if it hears only part of the call. Further, single notes within these complex calls can contain information enabling receivers to predict the sex of the signaler, and whether it is from the local population.