The least aggressive of the immature birds left the preferred beds first as the adults returned from the breeding grounds from July-October. The immatures that remained had similar aggression scores to adults. Aggressive encounters occurred much more frequently on preferred beds than on least preferred beds. There were highly significant differences in aggressiveness between individuals feeding on the most preferred beds, but not amongst those feeding on the low density bed. Intake rate was significantly correlated with aggressiveness amongst 18 individuals studied on the preferred beds but not amongst 18 individuals studied on the least preferred bed. This difference was probably mainly due to the amount of aggression, and, particularly of robbing, differing between the beds. On the most preferred beds, robbing depressed the intake of the less aggressive birds and enhanced that of the most aggressive ones. This was not the case on the least preferred bed as encounters were so rare. |
