During the hour before and the hour after sunset, the headings of flies relative to the position of the arena were recorded for 12 minutes. The arena was rotated 90 degrees every three minutes, and when natural light was not altered by optical filters some of the flies compensated for the rotations and maintained a consistent heading.

When the arena was covered with a circularly polarizing filter, eliminating natural linear polarization light patterns, the flies did not shift their heading significantly in response to arena rotations.