Visual mate detection in a territorial male butterfly (Asterocampa leilia): Effects of distance and perch location

We experimentally investigated proximate factors influencing the visual detection of flying conspecifics by male butterflies (Asterocampa leilia) engaged in a sit-and-wait mate-searching tactic. Model butterflies were presented to perched males in the field using an apparatus that permitted us to control the path and speed of a model while varying minimum distance of the model from the male, height of the model above the ground, and model size. The dependent Variable in all cases was whether or not the male left his perch and pursued the model. Males responded to normal-size models up to but not beyond distances of 3 m, and, because doubling the model surface area increased the distance at which males responded, we conclude that males do not detect conspecifics if they are more than 3 m away. At distances of 2 m or less males perched on the ground were more likely to detect conspecifics than males perched off the ground. This is likely to be due to differences either in the background against which the perched male typically views conspecifics or how large an angle conspecifics subtend from a perched male's perspective. These results suggest that thermally-driven changes during the activity period in perch preferences have consequences for success in mate detection that may be evolutionarily significant.