Linear mixed-model analysis of aggression scores shown by male fowl towards a manually presented intruder.

The aggression score (0 to 6) of a male towards a restrained intruder was used as response variable, and the aggression score (0 to 3) during the initial part of the duel was used as an explanatory variable, with the individual outcome of the duel as a fixed-effect factor (n = 31). Aggression towards a restrained intruder had a significant positive relationship with aggression during the duel.