Call Form in Relation to Function in the Steller's Jay

Abstract

Vocalizations of the Steller''s jay and of the scrub jay [Aphelocoma coerulescens] for comparison were recorded in the field and analyzed together with behavior to determine relationships between acoustic form and information conveyed. Call form is a combination of acoustic structures, selected and integrated by the requirements of each kind of information that the call conveys. Location appears to be conveyed by calls with wide band structure, especially over far range, by calls with rapid, regularly repeated transient notes at moderate range and possibly by Doppler effect in flight calls. Location apparently is concealed by diffuse onset combined with narrow band, by ventriloquism and by quietness. Threat calls are noisy or dissonant in tone, sustained in tempo and stress a moderately narrow range of low frequencies. Assertive calls with varied social functions are noisy, rhythmic and stress a wider range and higher frequencies than threat calls. Song, lacking a territorial function, is very quiet, primarily pure or resonant in tone, sustained or irregular in temporal character and complexly melodic. Appraisive information appears to be conveyed by continuous variation in rate of notes in at least 1 highly rhythmic call. Appraisive information probably is conveyed by gradation in design features that convey motivation. Between the steller''s jay and the scrub jay different features of form distinguish each of 3 calls that are probably homologous. The differences apparently are not species-isolating mechanisms, yet do show the trends that call divergence may take to convey species identity. Features of form than can be used to convey species identity may be those that can change because they are not constrained by acoustic form requirements of other kinds of information the call must convey.