Some male butterflies defend specific mating sites, e.g. sandy patches (Hipparchia semele) or plants (Ochlodes venata). When perching within its territory, a male orients the body axis and tilts its wings and body in order to control the body area exposed to the sun, and thereby keeps its body temperature (T b) as close to a preferred level as possible. In accordance with a model presented here, these behaviours can be separated into three successive phases. At low temperatures, the males maximized the heat load by exposing the maximum body area (sun-basking). This raised T b above the temperature of a non-regulating animal by c. 3° C. At an intermediate range of temperatures, T b was kept constant at the preferred level by means of a gradual change of body orientation and posture (graded phase). At high temperatures, the heat load was minimized by exposing the minimum body area. This lowered T b below that of a non-regulating animal by c. 2.5° C. H. semele went through all three phases, but O. venata only reached the basking phase due to a more moderate microclimate. Three types of thermoregulation in ectothermic animals and their functions are discussed. Thermoregulation in territorial male butterflies serves to prepare the animal for efficient flight performance if another male should try to take over the territory, or a predator attacks. The males also made frequent short flights, spontaneously or elicited by other insects. Their duration was independent of temperature, and they may function as a sexual signal.
Keywords: Behavioural thermoregulation; Butterflies; Sexual selection; Territoriality; Time budgets.