Orientation behaviour in the Grayling butterfly: thermoregulation or crypsis?

Abstract

ABSTRACT. Body orientation and wing tilting in Hipparchia semele (L.) have been explained previously both by the need for shadow‐minimization (crypsis hypothesis) and by the need to regulate body temperature (thermoregulation hypothesis). This study tests the thermoregulation hypothesis by quantifying butterfly orientation in relation to sun position, using vector analysis, and correlating the data with ambient temperature and time of day. During sunshine, Graylings tend to present a maximal wing area to the sun's rays when the ambient temperature is relatively low, and a minimal area when it is high ('sunning’and‘heat‐avoiding’positions respectively). On cool sunny days, butterflies adopt sunning positions throughout the day, whereas on warm sunny days they adopt sunning positions during the outlying periods and heat‐avoiding positions in the middle period of the day. Correlations between wing exposure and both ambient temperature and time of day are statistically significant for warm sunny days. During overcast weather, butterfly orientation is very variable and possibly random. Analysis of sunny day data supports the thermoregulation hypothesis. This is discussed in relation to other known types of thermoregulatory behaviour observed in this species: stilting, shade‐seeking, ground‐hugging and shivering. Conversely, the results do not support the crypsis hypothesis.