Fig. 4. Responses of monarch butterflies to 90° turns of polarizers or lids. Even though some monarchs changed their mean heading following a 90° clockwise turn of the 44° polarizer (A) or the 85° polarizer (without sun shades; B), their mean change was 0°. Furthermore, the animals' reactions in response to a turn of the polarizers were no different from their reactions when a lid with an opening exposing the blue sky was turned 90° (C). 0° indicates the mean direction chosen by each individual butterfly prior to the turn of the polarizer. Thus, a data point at 0° means that the orientation before and after the turn was identical. For explanation of symbols, see legend to Fig. 2.