AGGRESSIVE COMMUNICATION BY LARUS GLAUCESCENS .I. SOUND COMMUNICATION

The communicative functions of sound production during aggressive activity were studied by playing back the choking, trumpeting, mew, alarm and yelp calls to Larus glaucescens reacting aggressively to a mirror placed within its territory or by measuring the latency of attack on a stuffed model mounted in one of the display postures involved in aggressive activity. Differences between the experimental period with sound playback, and the control period with no sound playback were analyzed statistically by means of paired comparisons t-tests. As the result of these experiments the following conclusions were reached: I. The choking sound would inhibit the entrance of an intruder when produced by the territorial bird, but when produced by the intruder would stimulate the aggressive activity of the territorial resident. 2. The mew call functions similarly to the choking call but probably represents a somewhat lesser degree of aggressiveness. 3. The trumpeting call hastens an attack by a bird outside of its territory when produced within its territory and also stimulates aggressive activity of a bird within its territory, when produced by an intruder. 4. The alarm call inhibits aggressive activity, although it is not a usual part of aggressive activity. 5. The yelp call does not effect aggressive activity.