Postural changes accompany perch location changes in male butterflies (Asterocampa leilia) engaged in visual mate searching

Males of the nymphalid butterfly Asterocampa leilia perch and wait during t he morning at places where females are likely to appear. Males leave their perches to court passing females and chase away intruding males. As air and ground temperatures rise during the morning, males switch from perching on the ground to perching off the ground (average height = 0.87 m) for thermo regulatory reasons. To evaluate how this switch in perch location might aff ect mate detection, I have investigated how the three-dimensional posture o f the male's body and head varies with perch location and how conspecifics fly through male perching areas. The body posture of males varies with perc h location, as measured by pitch and roll relative to gravity, and yaw rela tive to the sun. Moreover, the pitch and roll of the head relative to the b ody is adjusted in a way that compensates for variation in body pitch and r oll. These results, along with information on conspecific flight altitudes, suggest that when a male is perched on the ground his visual system is pos itioned in such a way that he is less likely to detect conspecifics flying nearby than when he is perched off the ground. Hence, it appears that early in the morning visual detection of mates and intruding males may be compro mised by thermoregulatory concerns.