Territorial defence in the speckled wood butterfly ( Pararge aegeria): The resident always wins

Abstract

Males competed for territories, spots of sunlight on the ground layer of woodland, which were the best places for finding females. At any one time only 60% of the males had territories; the remainder patrolled for females up in the tree canopy. Males continually flew down from the canopy and rapidly took over vacant sunspots. However, if the sunspot was already occupied, then the intruder was always driven back by the owner. Experiments showed that this was true even if the owner had been in occupation for only a few seconds. The rule for settling contests was thus ‘resident wins, intruder retreats’. Experiments showed that escalated contests only occurred when both contestants ‘thought’ they were the resident. These results support the theoretical predictions of Maynard Smith & Parker (1976). The reason intruders accept defeat immediately without a serious fight may be that contests are costly and territories abundant.