TErritorial defence and mating success in males of the small heath butterfly, coenonympha pamphilus L. (Lepidoptera: Satyridae)

It has long been recognized that territorial defence in male butterflies must be some sort of mating strategy and that the territories are used as mating stations. However, so far, no systematic study has established the adaptive significance of territorial behaviour. This study is an attempt to fill this gap. By comparing the distribution of territories with the distribution of locations where wild and released virgin females mated this study shows that, in the small heath butterfly (Coenonympha pamphilus), males in territories have higher mating success than males outside territories. This supported the hypotheses that the function of territorial behaviour is to secure more matings and that the territories are mating stations. Wing length measurements suggest the same. Large males residing in territories tended to mate more often than small males, which were usually found outside territories. Since resident males were larger than non-resident males, this size difference was used to see how territorial occupancy influenced longevity. Mark-recapture of measured males revealed no significant correlation between wing length and the further life expectancy of males, strongly suggesting that the mating success of males in territories is also higher when measured over their whole lifetime.