Ludwig, J. P. 1964 Behavior: Aggressive behavior: Fighting, per se, is rare. This may be because territories are established. Actual contact was seen to occur only 3 times and each time the contact ended the aggressive behavior of both participants. In one case both birds immediately left the roost; once one bird left; and the third time both birds moved to a new place on the roost. I was able to distinguish 2 forms of hostile display. In the first case Boobies close together and already on the roost extend necks towards one another (sometimes only one bird does); if both birds extend necks the display ends after a short time with no contact. However, if one bird does not answer the threat by extending and facing, the other occasionally moves to attack. In all cases seen if the de- fending bird responds, this is enough to forstall or eliminate the incipient attack. Usually there is no voice. A second display is the Head-up-wings-lifted-tail-cocked display: This display is directed towards two classes of birds. a) Flying birds coming low over the roost showing signs of intending to land. Voice is a medium pitched reedy gurgle. It is directed towards the inflight bird and voice gets louder, wings raised more as the bird nears the roost (17 occasions). When given, the inflight bird always flew by the roost to come back later to try to land, often to be "warned away" several more times; b) towards birds already on the roost- voice- similar reedy gurgle, but lower pitched