Communication and spatial relationships in a colony of common grackles

Abstract

Most communication among common grackles Quiscalus quiscula occurs at distances of less than a few metres in the noisy environment of a breeding colony. This report examines both the adaptations of communication to these conditions and the effects of communication in regulating individuals' spatial relationships. For each of six vocalizations and five action patterns studied in one colony, I consider variation in the form of the display, the circumstances associated with its use, and the responses it elicits. Each individual, male or female, has one characteristic, stereotyped song pattern that would facilitate individual recognition between mates. Variation in the components of vocalizations and action patterns is of two kinds: unidimensional, with either covarying or nested components, or multidimensional, with independently varying components, alternatives that have different implications for communication. The wide-spectrum sounds made by common grackles offer advantages in close-range communication in colonies, because the ease of locating such signals would minimize the cocktail-party effect, although they would have disadvantages in long-range communication. Most vocalizations of common grackles lack associations with specific responses or external contexts, a situation that should often characterize short-range communication between acquainted individuals. The responses to vocalizations vary with context, especially the initial spatial relationships and identities of the interactors.