Pairs of complete models or wooden block models with adjustable stuffed heads of Larus glaucescens were placed in gull territories. Choice of attack on the models revealed that the head and neck of L. glaucescens are the parts of the body that release aggressive display in territorial behavior. When using models with the head and neck mounted in a normal posture, the upright threat model received a significantly greater number of attacks than the oblique model. The oblique model received a significantly greater number of attacks than the choking model. When comparing the reactions caused by the abnormal postured head at levels identical to those of the normal aggressive postures upright threat, oblique and choking, there were similar results. It was apparent that visual communication was accomplished by head level. A higher head level portrayed lower level of aggressiveness, whereas a lower head level portrayed greater level of aggressiveness and inhibited attack on the model. Secondary aggressive stimuli, such as squinted eyes and muscle tension, are probably not significant in evoking or prohibiting an attack.