Abstract and Summary

The vocal behavior of the pigeon guillemot (Cepphus columba) was studied for 5 years on Southeast Farallon Island, California in order to determine whether there were, rules common to many of the signals in the repertoire that could relate variation in signal structure to message content. The vocal displays used by pigeon guillemots in social communication are described, and variation in four vocal display classes (Hunch-whistles, FM notes, Screams, Trills) is quantitatively analysed.

Two sets of rules that relate signal structure to message content are proposed to describe variation in pigeon guillemot vocalizations. One set of rules relates continuous variation within each of the four vocal display classes to the signaller's probability of subsequent movement.

The second rule set, based on a simple hierarchy, regulates the assemblage of notes into higher-level units (phrases, displays) which encode progressively more information. Tape playback experiments confirmed an assumption made by this model: lower-level vocal elements contribute a specific message to each of the higher-level vocalizations in which they occur. The implications of this model for the perception of sounds and decoding of messages are discussed.